Situation and Perspectives on Tin-Based Perovskite Solar Cells

: Perovskite solar cells have become the current research focus because of their high conversion efﬁciency and other advantages; however, the toxicity of lead used in them has raised environmental concerns. Tin-based perovskite materials have become the most promising alternative materials for perovskite solar cells because of their relatively low toxicity, suitable band gap and relatively higher energy conversion efﬁciency than perovskite materials based on other elements. In this article, the status of this rapidly growing ﬁeld, authors’ output and cooperation, hot research topics, important references and the development trends of tin-based perovskite solar cells are iden-tiﬁed and visualized using CiteSpace software. The main research ﬁelds are found to be optical properties, 3D–2D perovskite and perovskite solar cell conduction band materials. The mixed organic metal halide perovskite solar cell and the CsSnI 3 semiconductor are identiﬁed as emerging trends for tin-based perovskite solar cells. Such contents in this article highlight the key points in the wide ﬁeld of literature so it can be understood efﬁciently.


Introduction
The photovoltaic performance of metal halide perovskite (MHP) materials has rapidly increased from 3.8% [1] to 25.2% [2] in the past decade, which shows their potential for future applications. Their great success is attributed to the unique ABX 3 crystal structure (where A is a monovalent organic or inorganic cation, B is a divalent cation and X is a monovalent anion), which provides ideal photovoltaic characteristics, including small exciton binding energy of several megaelectron volts (<25 megaelectron volts), and large electron hole mobility. In addition, the high efficiency of MHP is mainly attributed to Pb. Yet, the disadvantage of Pb is that it degrades with time, and its water solubility poses a serious threat to the environment, human beings and other species. Therefore, it is necessary to seek alternative materials with less toxicity.
In 2014, Hayase et al. [3] and Kanatzidis et al. [4] preliminarily studied the substitution of Sn for Pb in perovskite solar cells (PSCs), with the efficiencies 4.18% and 5.73% obtained, respectively. Borriello et al. [5] first proposed the application of tin halide perovskite to solar cells. They studied the structure and electronic characteristics of various tinbased perovskite and found that an inorganic cation structure has a great influence on the electronic characteristics of tin halide perovskite, and organic molecules must adapt to cubic octahedral pores formed by inorganic molecules. Since then, various tin-based PSCs have been continuously developed. The highest efficiency of tin-based PSCs is 14% [6] up to now, which is far ahead of other lead-free materials. Tin-based perovskite materials have become the most promising alternative materials for PSCs due to their relatively low toxicity, suitable band gap and high energy conversion efficiency.
At present, many researchers all over the world carry out research work around tin-based PSCs. Accordingly, in the face of a large number of documents created, it has become the first problem to be solved before conducting research to find the key documents

CiteSpace
CiteSpace is a widely used, multi-dimensional, time-sharing and dynamic thirdgeneration visual analysis tool for network information based on a JAVA platform developed by Professor Chaomei Chen of Drexel University in the United States. It can be obtained freely from the website of Professor Chaomei Chen at http://cluster.cis.drexel. edu/~cchen/citespace/ (accessed on 2 December 2022). There are also some other visualization tools, such as Histcite and Vosviewer. In comparison, Citespace can support more data formats from different databases and provide more analytical functions.
In this paper, CiteSpace 6.1.R2 was used to analyze the literature co-citation, for author analysis, keyword co-occurrence map analysis and keyword time zone map analysis in the field of tin-based PSCs, in order to explore the development status and research hotspots of this field. In total, 1061 articles from 2010 to May 2022 were analyzed, and time slice 1 was selected for analysis.

Annual Paper Publication
The first paper on tin-based perovskite, entitled "Controllable Synthesis of Welldispersed and Uniform-sized Single Crystalline Zinc Hydroxystannate Nanocubes", was published in 2010 [7]. In this paper, single crystal zinc hydroxystannate nanocubes were synthesized on α-{copper, tin} copper foil by the low-temperature hydrothermal method, and ZnSn(OH) 6 nanocubes with a cubic perovskite crystal structure were obtained on the substrate. Although this was not the classical ABX 3 fomula used widely later, the perovskite crystal structure was first correlated with tin-based materials in this paper. The number of papers published, as shown in Figure 1, indicates that research attention to tin-based PSCs has since increased continuously.
It can be seen from Figure 1 that the number of publications on tin-based PSCs increased rapidly in 2017. In this year, several important articles promoted the production of tin-based PSCs. Yuqin Liao et al. [8] found that the stability of low-dimensional tin halide perovskite thin films prepared could be significantly improved when using PEA as an organic isolation layer, and pure tin-based PSCs with an efficiency of 5.94% and stability lasting more than 100 hours were obtained. Liang Jia et al. [9] showed that an all-inorganic PSC based on CsPb 0.9 Sn 0.1 IBr 2 and a carbon counter electrode had a suitable band gap of 1.79 eV and a high open circuit voltage of 1.26 V, with the PCE as high as 11.33%. In addition to their good photo-to-electric conversion parameters, the cells also showed good stability, heat resistance and moisture resistance. These two highly cited articles, along with others, have provided great inspiration to the following researchers by promoting the development of tin-based PSCs, and the performance of such solar cells has been continuously improved with the efforts of the following researchers.
lasting more than 100 hours were obtained. Liang Jia et al. [9] showed that an all-inorganic PSC based on CsPb0.9Sn0.1IBr2 and a carbon counter electrode had a suitable band gap of 1.79 eV and a high open circuit voltage of 1.26 V, with the PCE as high as 11.33%. In addition to their good photo-to-electric conversion parameters, the cells also showed good stability, heat resistance and moisture resistance. These two highly cited articles, along with others, have provided great inspiration to the following researchers by promoting the development of tin-based PSCs, and the performance of such solar cells has been continuously improved with the efforts of the following researchers.

Co-authorship
CiteSpace was used to analyze the collaboration network of prolific authors. The selection criterion was the first 50% of each time period. A collaboration diagram is shown in Figure 2. The size of a circle represents the number of publications by corresponding authors. The shorter the distance between two circles, the more collaboration between the authors. The same color of the lines represents authors in the same group.

Co-Authorship
CiteSpace was used to analyze the collaboration network of prolific authors. The selection criterion was the first 50% of each time period. A collaboration diagram is shown in Figure 2. The size of a circle represents the number of publications by corresponding authors. The shorter the distance between two circles, the more collaboration between the authors. The same color of the lines represents authors in the same group.
Sustainability 2022, 14, x FOR PEER REVIEW 3 of 11 lasting more than 100 hours were obtained. Liang Jia et al. [9] showed that an all-inorganic PSC based on CsPb0.9Sn0.1IBr2 and a carbon counter electrode had a suitable band gap of 1.79 eV and a high open circuit voltage of 1.26 V, with the PCE as high as 11.33%. In addition to their good photo-to-electric conversion parameters, the cells also showed good stability, heat resistance and moisture resistance. These two highly cited articles, along with others, have provided great inspiration to the following researchers by promoting the development of tin-based PSCs, and the performance of such solar cells has been continuously improved with the efforts of the following researchers.

Co-authorship
CiteSpace was used to analyze the collaboration network of prolific authors. The selection criterion was the first 50% of each time period. A collaboration diagram is shown in Figure 2. The size of a circle represents the number of publications by corresponding authors. The shorter the distance between two circles, the more collaboration between the authors. The same color of the lines represents authors in the same group.  It can be seen that many authors tend to cooperate with a relatively stable group, resulting in several major author groups, each of which usually has two or more core authors, such as the clusters of Hayase S, Shen Q and Zhang X. The main core authors shown in Figure 2 also demark the most representative research groups in the field of tin-based PSCs. These groups provide highly personalized scientific research information for other researchers to work from. The top twenty most productive authors are listed in Table 1.

Co-Occurring Keywords Analysis
Co-occurring keywords reflect the research hotspots of tin-based perovskites. To study them, the 50 most frequently cited items from each slice were selected. As shown in Figure 3, nodes represent keywords, and the size of each node corresponds to its frequency of occurrence. The colors of the links that appear together between the keywords indicate the chronological order: the oldest is white, and the newest is green.
It can be seen that many authors tend to cooperate with a relatively stable group, resulting in several major author groups, each of which usually has two or more core authors, such as the clusters of Hayase S, Shen Q and Zhang X. The main core authors shown in Figure 2 also demark the most representative research groups in the field of tin-based PSCs. These groups provide highly personalized scientific research information for other researchers to work from. The top twenty most productive authors are listed in Table 1.

Co-occurring Keywords Analysis
Co-occurring keywords reflect the research hotspots of tin-based perovskites. To study them, the 50 most frequently cited items from each slice were selected. As shown in Figure 3, nodes represent keywords, and the size of each node corresponds to its frequency of occurrence. The colors of the links that appear together between the keywords indicate the chronological order: the oldest is white, and the newest is green.  The top 10 keywords with the number of citations are shown in Table 2, among which the most cited keyword is "solar cell". The nodes marked with purple circles mostly indicate good centrality and the importance of these keywords. The centrality of "high performance" and "iodide perovskite" is 0.07, and the centrality of "low cost" is 0.10. In order to further analyze the time pattern of how keyword clusters have evolved, information about frequently repeated terms and clusters was converted into a timeline view, as shown in Figure 4. In the timeline visualization, clusters are displayed horizontally along the timeline, with the label of each cluster displayed at the end of the cluster timeline. The legend above the display area is marked every five years, and in each year only the top three keywords with the highest count are displayed along each timeline. The color of the link between the keywords represents the time slice of the first co-occurrence. The top 10 keywords with the number of citations are shown in Table 2, among which the most cited keyword is "solar cell". The nodes marked with purple circles mostly indicate good centrality and the importance of these keywords. The centrality of "high performance" and "iodide perovskite" is 0.07, and the centrality of "low cost" is 0.10.  Keywords  361  solar cell  292  halide perovskite  260  stability  232  performance  203  perovskite solar cell  187  efficiency  172  efficient  112  fabrication  111  iodide  110 tin In order to further analyze the time pattern of how keyword clusters have evolved, information about frequently repeated terms and clusters was converted into a timeline view, as shown in Figure 4. In the timeline visualization, clusters are displayed horizontally along the timeline, with the label of each cluster displayed at the end of the cluster timeline. The legend above the display area is marked every five years, and in each year only the top three keywords with the highest count are displayed along each timeline. The color of the link between the keywords represents the time slice of the first co-occurrence.

Citation Counts
For example, cluster #1 "phase transition" started in 2013 and lasted until 2022. In this cluster, the first keyword "solar cell" appears most frequently. Other frequently used keywords include "band gap", "perovskite solar cell", "optical property", etc.

Literature Co-citation Analysis
The selection criteria were the top 50 most frequently cited items from each slice, as shown in Figure 5. Accordingly, 801 unique nodes, 4654 connections and 9 main clusters were generated. The modularity Q was 0.6095, and the average profile S was 0.867. The nodes and lines represent references and co-citation relationships cited from collected articles, respectively. The connection colors directly correspond to the time slices, with cold colors representing earlier years and warm colors representing recent years. For example, For example, cluster #1 "phase transition" started in 2013 and lasted until 2022. In this cluster, the first keyword "solar cell" appears most frequently. Other frequently used keywords include "band gap", "perovskite solar cell", "optical property", etc.

Literature Co-Citation Analysis
The selection criteria were the top 50 most frequently cited items from each slice, as shown in Figure 5. Accordingly, 801 unique nodes, 4654 connections and 9 main clusters were generated. The modularity Q was 0.6095, and the average profile S was 0.867. The nodes and lines represent references and co-citation relationships cited from collected articles, respectively. The connection colors directly correspond to the time slices, with cold colors representing earlier years and warm colors representing recent years. For example, purple links describe articles that were co-cited in 2013, and the most recent co-citing purple links describe articles that were co-cited in 2013, and the most recent co-citing relationship is visualized by yellow links. Q > 0.3 indicates that the network is significant, and S > 0.5 indicates that the clustering result is reasonable. As shown in Figure 5, the main research fields can be grouped into several clusters: perovskite, lead-free, tin perovskite, crystal structure, all-inorganic perovskites, lead-free systems, interfacial dipole, etc. The lead author and publishing time of the most cited papers in each field are also shown, which provides readers with clues to find articles of interest.
The top 10 most cited papers for tin-based PSCs are listed in Table 3 [4,8,[10][11][12][13][14][15][16]. Highly correlated nodes can be considered as important bridges between studies. Nakita et al. [10] produced the first completely lead-free CH3NH3SnI3 PSC. The structure of the perovskite-sensitized solar cell (PSSC) is FTO-coated glass/compact TiO2/mesoporous-TiO2 (400 nm) coated with CH3NH3SnI3/Spiro-OMeTAD/Au. Encapsulation of this material under an inert atmosphere allowed them to characterize the films and probe their performance in solar cells. An efficiency of more than 6% under 1 sunlight and an open circuit voltage of more than 0.88V were obtained from CH3NH3SnI3 with a band gap of 1.23 eV.
It was a challenge to fabricate efficient FASnI3 PSCs because it was necessary to deposit uniform and dense perovskite layers and reduce the Sn 4+ content. In order to solve this problem, solvent engineering and solvent-free dripping technology were used by Lee et al. [11]. They found that pyrazine could restrict the phase separation induced by the use of excess SnF2 through an interaction with SnF2 that reduced the Sn vacancies effectively. With SnF2 used as the inhibitor of Sn 4+ , a 4.8% power conversion efficiency was achieved.
Feng Hao et al. [4] combined CH3NH3SnI3 (1.3 eV) perovskite materials with organic hole transport layers in solar cell devices, which begin to absorb at 950 nanometers. In comparison with CH3NH3PbI3 (1.55 eV), the absorption band was significantly shifted. The efficiency of the CH3NH3SnI3-xBrx solar cell was converted to 5.73% under simulated sunlight, which is a step toward low-cost, environmentally friendly solid-state solar cells.
Liao WQ et al. [12] described the performance of inverted planar formamidinium tin triiodide (FASnI3) PSCs, showing the highest PCE of 6.22%. Shao et al. [13] achieved up to 9.0% PCE for the first time in a planar p-i-n device structure. Liao YQ et al. [8] achieved pinhole-free films by manipulating the film composition, which prevents oxygen from diffusing into the chalcogenide lattice. Based on these advances, they constructed pure tin PSCs with the efficiency up to 5.94%. Yang WS et al. [14] found that the introduction of As shown in Figure 5, the main research fields can be grouped into several clusters: perovskite, lead-free, tin perovskite, crystal structure, all-inorganic perovskites, lead-free systems, interfacial dipole, etc. The lead author and publishing time of the most cited papers in each field are also shown, which provides readers with clues to find articles of interest.
The top 10 most cited papers for tin-based PSCs are listed in Table 3 [4,8,[10][11][12][13][14][15][16]. Highly correlated nodes can be considered as important bridges between studies. Nakita et al. [10] produced the first completely lead-free CH 3 NH 3 SnI 3 PSC. The structure of the perovskitesensitized solar cell (PSSC) is FTO-coated glass/compact TiO 2 /mesoporousTiO 2 (400 nm) coated with CH 3 NH 3 SnI 3 /Spiro-OMeTAD/Au. Encapsulation of this material under an inert atmosphere allowed them to characterize the films and probe their performance in solar cells. An efficiency of more than 6% under 1 sunlight and an open circuit voltage of more than 0.88V were obtained from CH 3 NH 3 SnI 3 with a band gap of 1.23 eV.
It was a challenge to fabricate efficient FASnI 3 PSCs because it was necessary to deposit uniform and dense perovskite layers and reduce the Sn 4+ content. In order to solve this problem, solvent engineering and solvent-free dripping technology were used by Lee et al. [11]. They found that pyrazine could restrict the phase separation induced by the use of excess SnF 2 through an interaction with SnF 2 that reduced the Sn vacancies effectively. With SnF 2 used as the inhibitor of Sn 4+ , a 4.8% power conversion efficiency was achieved.
Feng Hao et al. [4] combined CH 3 NH 3 SnI 3 (1.3 eV) perovskite materials with organic hole transport layers in solar cell devices, which begin to absorb at 950 nanometers. In comparison with CH 3 NH 3 PbI 3 (1.55 eV), the absorption band was significantly shifted. The efficiency of the CH 3 NH 3 SnI 3-x Br x solar cell was converted to 5.73% under simulated sunlight, which is a step toward low-cost, environmentally friendly solid-state solar cells.
Liao WQ et al. [12] described the performance of inverted planar formamidinium tin triiodide (FASnI 3 ) PSCs, showing the highest PCE of 6.22%. Shao et al. [13] achieved up to 9.0% PCE for the first time in a planar p-i-n device structure. Liao YQ et al. [8] achieved pinhole-free films by manipulating the film composition, which prevents oxygen from diffusing into the chalcogenide lattice. Based on these advances, they constructed pure tin PSCs with the efficiency up to 5.94%. Yang WS et al. [14] found that the introduction of 179 Lead-free organic-inorganic tin halide perovskites for photovoltaic applications Eperon, G. E et al. [15] developed an infrared absorption 1.2 eV band gap perovskite, FA (0.75) Cs (0.25) Sn (0.5) Pb (0.5) I (3) , which provided 14.8% efficiency. By combining this material with the wide-band-gap FA (0.83) Cs (0.17) Pb(I 0.5 Br 0.5 ) material, a single-chip double-terminal series efficiency of 17.0% was achieved at an open circuit voltage greater than 1.65 V. The four-terminal series cell was mechanically stacked, and an efficiency of 20.3% was obtained. The infrared-absorbing PSC showed excellent thermal stability and atmospheric stability.
Feng Hao et al. [16] verified that CH 3 NH 3 Sn 0.5 Pb 0.5 I 3 had the broadest light absorption and the highest short-circuit photocurrent density of about 20 mA cm −2 . Stoumpos C. C. et al. [17] concluded that the hybrid perovskite material (CH 3 NH 3 Sn 1−x Pb x I 3 ) is a flexible and versatile functional material. Capable of emitting light in the near-infrared spectral region at room temperature, it was shown to be a promising candidate for a good electrical conductor and a powerful emitter at room temperature.

Emerging Trends
The significant increase in research interest in the field of tin-based PSCs is highlighted by publications' cited keywords. The top 38 keywords with the strongest citation bursts in 1061 articles from 2010 to May 2022 are shown in Table 4.
As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell,  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020.   Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell   Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell,  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell,  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020.  Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, As shown in Table 4, the first keyword "dye-sensitized solar cells" began to explode in 2010 and continued until the end of 2018. The research hotspots have changed in the last two years; keywords such as "methylammonium", "durability", "fasni(3) crystal", "impact", "ion migration" and "defect passivation" started to explode in 2021 and are still in the process of exploding in 2022, becoming new emerging trends.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020.
The keyword "phase transition" with top intensity 9.16 started to erupt from 2014 to 2017. The keyword "semiconductor" with top intensity 6.78 started to erupt from 2014 to 2017. The keyword "transport" with top intensity 5.74 started to erupt from 2013 to 2016. The keyword "high performance" with top intensity 5.43 started to erupt from 2014 to 2016. Among those keywords, "phase transition" has been the hottest topic in solar cell technology in recent years. Figure 6 shows representative references. The strength of the citation bursts may reflect the rise and fall of tin-based PSCs. The reference with the strongest citation butst was published by Michael M. Lee et al. [18] in 2012. The outbreak lasted from 2013 to 2020. The authors introduced a high-efficiency hybrid organic metal halide perovskite solar cell, which uses a high crystalline perovskite absorbent with strong visible light and near-infrared absorption characteristics. The solar cell structure is FTO/compact which uses a high crystalline perovskite absorbent with strong visible light and near-infrared absorption characteristics. The solar cell structure is FTO/compact TiO2/CH3NH3PbI2Cl/spiro-OMeTAD/Ag, simulating full sunlight, and the power conversion efficiency in a single junction device is 10.9%. Burschka J et al. [19] used the sequential deposition method as a way to manufacture high-performance perovskite-sensitized solar cells, and a photoelectric conversion efficiency of 15% was achieved. Stranks SD et al. [20] illustrated that with the correct tuning of the perovskite absorber, no nano or mesostructures were required for efficient charge generation and collection. This result paved the way for further development of planar heterogeneous perovskite solar cells.
Liu MZ et al. [21] found that perovskite absorbers could function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures. Lin RX et al. [22] fabricated monolithic all-perovskite tandem cells with certified PCEs of 24.8%. Among these works, "Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites", published by Michael M. Lee et al. [18], presents the emerging trend of tin-based PSCs.

Timezone Analysis
To understand the evolution of this research field, we can analyze it from two aspects: popular keywords used with the development of the academic field, and the use of specific keywords or their sudden detection in the citations of specific articles. To test these out, keyword data were formatted into a time zone view, as shown in Figure 7, which presents popular phrases (2010-May 2022) used over 12 years and 5 months.
As early as 2010, the keywords "sensitized solar cell" appeared in related articles, indicating that early entry into this field was related to dye-sensitized solar cells. Subsequently, the most frequently repeated keywords in 2013-2016, such as "low cost", "phase transition", "semiconductor" and "deposition", explained the prospects and framework of tin-based PSCs.
In 2014, "phase transition" was widely mentioned and seems to have been the focus. After further retrieval, it was found that Stoumpos, C. C. published a paper in 2013 entitled "Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties". They studied the effect of phase transformation at different temperatures on the PL properties of CsSnI3 Burschka J et al. [19] used the sequential deposition method as a way to manufacture high-performance perovskite-sensitized solar cells, and a photoelectric conversion efficiency of 15% was achieved. Stranks SD et al. [20] illustrated that with the correct tuning of the perovskite absorber, no nano or mesostructures were required for efficient charge generation and collection. This result paved the way for further development of planar heterogeneous perovskite solar cells.
Liu MZ et al. [21] found that perovskite absorbers could function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures. Lin RX et al. [22] fabricated monolithic all-perovskite tandem cells with certified PCEs of 24.8%. Among these works, "Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites", published by Michael M. Lee et al. [18], presents the emerging trend of tin-based PSCs.

Timezone Analysis
To understand the evolution of this research field, we can analyze it from two aspects: popular keywords used with the development of the academic field, and the use of specific keywords or their sudden detection in the citations of specific articles. To test these out, keyword data were formatted into a time zone view, as shown in Figure 7, which presents popular phrases (2010-May 2022) used over 12 years and 5 months.
As early as 2010, the keywords "sensitized solar cell" appeared in related articles, indicating that early entry into this field was related to dye-sensitized solar cells. Subsequently, the most frequently repeated keywords in 2013-2016, such as "low cost", "phase transition", "semiconductor" and "deposition", explained the prospects and framework of tin-based PSCs.
In 2014, "phase transition" was widely mentioned and seems to have been the focus. After further retrieval, it was found that Stoumpos, C. C. published a paper in 2013 entitled "Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties". They studied the effect of phase transformation at different temperatures on the PL properties of CsSnI3 and proposed that hybrid iodized perovskite is a flexible, multi-purpose functional material emitted at room temperature in the near-infrared spectral region, which has a suitable band gap and large carrier mobilities [17]. This paper has been cited 3748 times, which proves research on phase transition is very popular. and proposed that hybrid iodized perovskite is a flexible, multi-purpose functional material emitted at room temperature in the near-infrared spectral region, which has a suitable band gap and large carrier mobilities [17]. This paper has been cited 3748 times, which proves research on phase transition is very popular.
Since then, keywords have become more and more fragmented, indicating the stable and consistent development of this academic field. In the past two years (2019-2021), "TiO2", "phase" and "carrier lifetime" have been thematic research hotspots.

Conclusions
The co-citations and visualization network of references for tin-based PSCs were studied using CiteSpace. Key articles, identified research patterns and emerging trends in the literature were then explored based on the findings of CiteSpace. Cluster visualization based on the document co-citation network showed that the main research fields are perovskite, lead-free, tin perovskite, crystal structure, all-inorganic perovskites, lead-free systems and interfacial dipole. The citation burst analysis indicated that topics concerning stability, such as durability, impact, ion migration and defect passivation, as well as FaSnI3 crystal, have still been research hotspots in recent years and may continue to be in the future. These results can help readers to grasp the development history, future trends and key technologies of the tin-based PSC field more efficiently. Due to the interdisciplinary characteristics of tin-based PSCs, it is difficult to give a complete picture of the research field. However, we have demonstrated a quantitative scientific measurement method to explore the development of tin-based PSCs, using references published in this field, to intuitively and effectively determine the patterns and trends in this field.

Conclusions
The co-citations and visualization network of references for tin-based PSCs were studied using CiteSpace. Key articles, identified research patterns and emerging trends in the literature were then explored based on the findings of CiteSpace. Cluster visualization based on the document co-citation network showed that the main research fields are perovskite, lead-free, tin perovskite, crystal structure, all-inorganic perovskites, lead-free systems and interfacial dipole. The citation burst analysis indicated that topics concerning stability, such as durability, impact, ion migration and defect passivation, as well as FaSnI 3 crystal, have still been research hotspots in recent years and may continue to be in the future. These results can help readers to grasp the development history, future trends and key technologies of the tin-based PSC field more efficiently. Due to the interdisciplinary characteristics of tin-based PSCs, it is difficult to give a complete picture of the research field. However, we have demonstrated a quantitative scientific measurement method to explore the development of tin-based PSCs, using references published in this field, to intuitively and effectively determine the patterns and trends in this field.