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Article

Investigation on Film Quality and Photophysical Properties of Narrow Bandgap Molecular Semiconductor Thin Film and Its Solar Cell Application

Beijing Advanced Innovation Center for Materials Genome Engineering, Research Center for Sensor Technology, Beijing Key Laboratory for Sensor, Beijing Key Laboratory for Optoelectronic Measurement Technology, MOE Key Laboratory for Modern Measurement and Control Technology, School of Applied Science, Beijing Information Science and Technology University, Jianxiangqiao Campus, Beijing 100101, China
*
Author to whom correspondence should be addressed.
Coatings 2021, 11(11), 1300; https://doi.org/10.3390/coatings11111300
Submission received: 18 September 2021 / Revised: 13 October 2021 / Accepted: 18 October 2021 / Published: 27 October 2021
(This article belongs to the Special Issue Advanced Perovskite Films for Photovoltaic Application)

Abstract

:
Hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) is one of the narrowest bandgap molecular semiconductor reported in recent years. Through the study of its energy band structure, it can be identified as an N-type semiconductor and is able to absorb most of the visible light, making it suitable to fabricate solar cells. In this paper, SnO2 was used as an electron transport layer in HDA-BiI5-based solar cells, for its higher carrier mobility compared with TiO2, which is the electron transport layer used in previous researches. In addition, the dilution ratio of SnO2 solution has an effect on both the morphology and photophysical properties of HDA-BiI5 films. At the dilution ratio of SnO2:H2O = 3:8, the HDA-BiI5 film has a better morphology and is less defect inside, and the corresponding device exhibited the best photovoltaic performance.

1. Introduction

In recent years, solar cells have achieved rapid development, especially the third-generation solar cells [1,2,3]. Researchers have also started to experiment with various new materials to develop solar cells with better performance [4,5,6]. The molecular semiconductor with the narrowest bandgap of 1.89 eV, hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5), was reported by Zhang et al. in 2017 and was concluded to be an indirect bandgap semiconductor [7]. It was also reported in 2016 as a hybrid organic-inorganic material by Fabian et al. [8]. They identified HDA-BiI5 as an N-type semiconductor by its energy band structure. With the narrow bandgap, HDA-BiI5 is able to absorb most of the ultraviolet-visible (UV-vis) light from sunlight, making it more suitable than other molecular semiconductors for use as a light absorption layer in solar cells.
Up to now, two types of HDA-BiI5-based photovoltaic devices have been reported. Fabian et al. [8] used a mesoporous structure with TiO2 and 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (Spiro-MeOTAD) as the electron transport layer (ETL) and the hole transport layer (HTL), respectively. A photocurrent of 0.124 mA/cm2 and a power conversion efficiency (PCE) of 0.027% were obtained. Liu et al. [9] prepared HDA-BiI5-based solar cells with only TiO2 as the ETL and no HTL in 2020. They realized an open-circuit voltage (Voc) of 0.55 V and a short-circuit current density (Jsc) of 17.5 µA/cm2. The value of PCE is not given, but according to the current-voltage (J-V) curve, it is an order of magnitude lower than that of Fabian et al. A comparison revealed that only one material, TiO2, had been tried for the electron transport layer, and perhaps the devices could be optimized from this aspect.
SnO2 has a higher carrier mobility than that of TiO2, [10,11], which may be able to improve the device performance, forming better interfacial contact and efficient transport of photo-generated electrons [12,13]. In this paper, the energy band structure of HDA-BiI5 thin films, as well as their film morphology and photophysical properties on ITO/SnO2 substrates, are investigated in detail. In addition, whether the dilution ratio of SnO2 to H2O during the preparation of the SnO2 layer has any effect on the morphology and photophysical properties of HDA-BiI5 films was carried out, [14,15,16,17,18,19] and the corresponding solar cells were fabricated.

2. Materials and Methods

2.1. Preparation of Device

To start, 100 mL of HI solution was mixed with 5.9 g (10.0 mmol) of BiI3 powder in a round bottom flask and was stirred for about 1 h at room temperature on a temperature-controlled digital magnetic stirrer to dissolve it fully. After the internal temperature reached 90 °C and stabilized, 1.16 g (10.0 mmol) of 1.6-hexanediamine crystals was added and stirred magnetically while heating for 12 h to dissolve and react with 1,6-hexanediamine crystals. After that, the solution in the flask was poured into a clean beaker and placed on an intelligent temperature-controlled baking table, and the solution in the beaker was slowly evaporated and crystallized at 90 °C until dark red crystals. HDA-BiI5 crystals were precipitated at the bottom of the beaker. The crystals were scraped from the beaker with a glass rod, grinded into a powder, and placed into a small glass vial, which was then sealed with a sealant and kept as a reserve.
Indium tin oxide (ITO) was selected as the substrate and cleaned using detergent, isopropanol and acetone mixture, ethanol, and deionized water in turn. Regarding the preparation of SnO2 ETL, 300 μL of SnO2 solution was mixed with 600, 800, 1000, 1200, and 1400 μL of ultrapure water to make up a solution with dilution ratios of 3:6, 3:8, 3:10, 3:12 and 3:14, respectively. It was then mixed well by ultrasonication. The five different dilution ratios of SnO2 solutions were spin-coated onto the conductive substrates at a rate of 4000 rpm for 30 s. Immediately after spin-coating, the films were annealed on a hot plate at 150 °C for 30 min. UV ozonation was performed for 15 min after annealing to provide a better hydrophilic surface for the spin-coating of the light absorption layer.
In the preparation of HDA-BiI5 films, 500 mg of stored HDA-BiI5 powder was taken out and poured into a small clean transparent glass vial, followed by 0.4 mL of DMF solution as solvent. The glass vial with the solution was put into the ultrasonic cleaning equipment for 3 h until the powder was completely dissolved in the DMF solvent, and then the solution was filtered with a 0.22-μm-diameter filter nozzle to complete the preparation of HDA-BiI5 precursor solution. Next, 40 μL of HDA-BiI5 precursor solution was uniformly coated on the ITO/SnO2 substrate, and spun for 40 s at a rate of 6000 rpm. Immediately after spin-coating, it was annealed on a hot plate at 150 °C for 30 min. After annealing, the HDA-BiI5 light absorption layer was also prepared.
The HTL was prepared using the directly purchased Spiro-MeOTAD spin-coating solution. Then, 20 μL of Spiro-MeOTAD spin-coating solution was pipetted and spin-coated at 3000 rpm for 30 s. After spin-coating, it was annealed on a hot plate at 60 °C for 8 min. Finally, an 80-nm-thick gold electrode was thermally evaporated on the HTL. The effective area of the prepared photovoltaic devices was 0.2 × 0.2 cm2.

2.2. Characterization

The surface morphology of HDA-BiI5 thin films was characterized by scanning electron microscope (SIGMA, Zeiss, Jena, Germany). The X-ray diffraction (XRD) patterns were obtained from X-ray diffractometer (D8 focus, Bruker, Dresden, Germany) with Cu radiation (λ = 1.5418 Å) at 40 kV, 40 mA. Energy dispersive X-ray spectroscopy (EDS) was used to analyze the elemental composition of the film. Ultraviolet photoemission spectroscopy (UPS) was used to determine the electronic band structure of the HDA-BiI5 thin film. A photoluminescence spectrometer (FluoroMax-Plus, HORIBA Scientific, Paris, France) was applied to obtain the photoluminescence spectra (PL) of light absorption layer films at 370 nm. The current–voltage (J-V) curve of the solar cells was measured by using a solar simulator and an electrochemical workstation (Oriel, Newport, RI, USA) under air-mass (AM) 1.5 sunlight.

3. Results and Discussion

The morphology of HDA-BiI5 films prepared on SnO2 layers spin-coated with five dilution ratios is shown in Figure 1. As can be seen from the figures, when the SnO2/H2O dilution ratio is 3:6, there are a lot of cracks and holes on the surface of HDA-BiI5 film, and the grain boundaries cannot be obviously distinguished. Such cracks and holes may make contact between the hole transport layer and the electron transport layer in solar cells, resulting in electrical leakage. When the ratio SnO2:H2O = 3:8 is used to prepare the SnO2 layer, the grain boundaries of HDA-BiI5 thin film are obvious, and the surface is smooth with no obvious cracks. Although there are still a few holes, they are relatively small, illustrating that the film quality is improved. When the SnO2/H2O dilution ratio is 3:10, obvious cracks and large holes appear again on the surface of the HDA-BiI5 film, and the grain boundaries become blurred. After continuously adjusting the dilution ratio to 3:12 and 3:14, the cracks and holes on the surface of the HDA-BiI5 film continue to increase and increase, making it difficult to distinguish single crystal particles.
Figure 2 shows XRD patterns of HDA-BiI5 thin films deposited on “Glass/ITO/SnO2” substrates. The main diffraction peak locations and corresponding crystal planes marked in the figure are basically consistent with the XRD characteristics of the HDA-BiI5 thin films reported by Fabian et al. [8] and Zhang et al. [7], constituting a primitive orthorhombic crystal structure of space group Pna21, a = 15.1729(11), b = 14.3521(13), c = 8.6623(7) Å (at 296 K) [7]. It can be seen from the figure that the XRD characteristic curves of HDA-BiI5 thin films on SnO2 layers prepared with five dilution ratios are similar, which indicates that the lattice structure of the thin films was not changed. In addition, with the dilution ratio of SnO2 to H2O from 3:6 to 3:8, the peak strength slightly increases and reaches the highest at the ratio of 3:8, and then it slightly decreases as the ratio continues to change to 3:10, 3:12, and 3:14. This indicates that the crystallinity of the HDA-BiI5 thin film prepared when the dilution ratio of SnO2 to H2O is 3:8 is the best, which is also consistent with the morphology characteristics of the HDA-BiI5 thin film observed in Figure 1.
The best quality film deposited on the “Glass/ITO/SnO2” substrate with SnO2:H2O = 3:8 in Figure 1b was analyzed by EDS, as shown in Figure 3 below. The presence of each element of the HDA-BiI5 in the energy spectrum can be seen from the figure, which, together with the XRD results, verifies the accuracy of the prepared HDA-BiI5 films. In addition, the presence of Sn elements may be due to the ITO substrate and the SnO2 layer.
Figure 4 shows the ultraviolet-visible (UV-vis) absorption spectra of the HDA-BiI5 films on SnO2 layers prepared with SnO2 and H2O in five dilution ratios of 3:6, 3:8, 3:10, 3:12, and 3:14, respectively. The photo absorption range of the HDA-BiI5 films prepared on the five different SnO2 layers is basically the same, and the corresponding Tauc plot shows that the bandgap of the HDA-BiI5 material in our experiment is about 1.94 eV, which is close to the previously reported 1.89 eV [7].
The energy band structure of HDA-BiI5 thin film was measured by UPS, as shown in Figure 5. The Fermi energy level is corrected to 0 eV using a gold standard sample, and a bias voltage of −10 eV is applied to test the power function. The power function is calculated as follows in Equation (1).
φ s = h v ( E c u t o f f E F ) = h v E c u t o f f + E F
where hv is the excitation source energy, the HeII UV source used in this experiment is 21.22 eV; Ecutoff is the cutoff binding energy, as seen in the left figure; the cutoff binding energy is 16.21 eV; and EF is the Fermi energy level, which was corrected to 0 eV during the test, so the calculated work function of HDA-BiI5 is 5.01 eV. In order to further determine the valence band maximum (VBM) position of the material, tangent lines are made in the right figure, as shown in the red line, and the binding energy at the intersection point is 1.57 eV. Therefore, the VBM of the material is −6.58 eV. Based on the band gap of the material obtained from the absorption spectrum, the conduction band bottom of the material can be calculated as −4.64 eV, and its Fermi energy level is −5.01 eV which is closer to the CBM, indicating that the material is an N-type semiconductor. Although both are identified as N-type semiconductors, the VBM of HDA-BiI5 in this paper differs from the data reported in 2016 by nearly 1 eV. The measured optical bandgap of the material also differs from the 2.1 eV reported in 2016 and the 1.89 eV in 2017. In particular, the CBM of HDA-BiI5 in Fabian et al.’s research is higher than that of TiO2 so that electrons can smoothly transport from HDA-BiI5 to TiO2; however, in this experiment, the calculated CBM of HDA-BiI5 is lower than that of SnO2, so there can be a potential barrier for electron transport from the light absorption layer to the ETL. Furthermore, among the commonly used materials for electron transport, there are none that can match the −4.64 eV CBM.
Figure 6 shows the photoluminescence spectra of HDA-BiI5 films prepared on “Glass/ITO/SnO2” substrates at the different dilution ratio of SnO2 to H2O. The excitation wavelength of the test is 370 nm and the scanning wavelength is between 450 and 850 nm. The main emission peaks of the films can be seen in the range of 500 to 700 nm, mainly due to the semiconductor bandgap luminescence, while other reasons, such as surface defects, may be responsible for the other lower emission peaks. When the dilution ratio of SnO2 to H2O is 3:8, the PL peaks of the prepared HDA-BiI5 films are the lowest. Combined with the SEM morphology of the HDA-BiI5 films at SnO2: H2O = 3:8, the morphology of the film is the best among the five species, and the defects in the film are correspondingly less, so the recombination of the photogenerated carriers in the PL test are the least, illustrating the forming of a better charge transportation between the HDA-BiI5 film and the SnO2 layer among the five cases. After that, with the increase in the proportion of H2O in the SnO2 solution, the PL peak of the HDA-BiI5 film becomes higher again. Combined with the analysis of the SEM diagram in Figure 1, it may be that the lower the concentration of the SnO2 solution diluted, the poorer the quality of the formed SnO2 layer, the sparser the crystal growth, and the rougher the surface, which in turn leads to the poor quality of the HDA-BiI5 film and the increase in the internal defects, making the exciton radiation recombination increase, and the electron generated in HDA-BiI5 layer cannot be effectively transferred into the SnO2 electron transport layer.
The corresponding solar cells were fabricated using different SnO2 precursor solution concentrations; their J-V curves are shown in Figure 7. Consistent with the studies on the film quality and photophysical properties above, the photovoltaic performance of the devices also reached the maximum at SnO2:H2O = 3:8; the photovoltaic parameters are shown in detail in Table 1. The distribution of the performance parameters of the other devices we prepared with a dilution ratio of SnO2:H2O = 3:8 is shown in Figure 8, where the parameters are relatively close to each other, as seen in Table 2, proving the reliability and reproducibility of the study results. Further work can be carried out to improve the device performance by reducing energy level mismatches, such as using composite ETL and other preparation methods of SnO2 [20,21,22].

4. Conclusions

In this paper, HDA-BiI5 thin films were prepared on ITO/SnO2 substrates, and the film quality, energy band structure, and photophysical properties of the films were investigated in detail. It was found that its conduction band minimum was −4.64 eV, which does not match well with any of the widely used electron transport materials, which is a problem to be solved in the application of HDA-BiI5 in photovoltaic field. In addition, the dilution ratio of SnO2 to H2O in the preparation of SnO2 layers can affect the morphology and photophysical properties of HDA-BiI5 films. The corresponding solar cells also exhibited the best performance at the 3:8 dilution ratio, showing a PCE of 0.0022 ± 0.0002%. This work can provide references and ideas for the selection and optimization of ETL in the fabrication of HDA-BiI5-based solar cells.

Author Contributions

Conceptualization, J.L. and C.Z.; methodology, G.L.; software, J.C.; validation, X.Z.; formal analysis, G.L. and X.L.; investigation, X.L.; resources, G.L.; data curation, X.L. and Y.W.; writing—review and editing, X.L.; visualization, X.W., K.S. and B.R.; supervision, X.Z.; funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (No. 61875186 and No. 61901009), State Key Laboratory of Advanced Optical Communication Systems Networks of China (2021GZKF002) and Beijing Key Laboratory for Sensors of BISTU (No. 2019CGKF007).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kim, G.; Min, H.; Lee, K.S.; Lee, D.Y.; Yoon, S.M.; Seok, S.I. Impact of strain relaxation on performance of alpha-formamidinium lead iodide perovskite solar cells. Science 2020, 370, 108–112. [Google Scholar] [CrossRef]
  2. Wu, T.H.; Qin, Z.Z.; Wang, Y.B.; Wu, Y.Z.; Chen, W.; Zhang, S.F.; Cai, M.L.; Dai, S.Y.; Zhang, J.; Liu, J.; et al. The main progress of perovskite solar cells in 2020–2021. Nano-Micro Lett. 2021, 13, 152. [Google Scholar] [CrossRef]
  3. Zhao, W.J.; Xu, J.; He, K.; Cai, Y.; Han, Y.; Yang, S.M.; Zhan, S.; Wang, D.P.; Liu, Z.K.; Liu, S.Z. A special additive enables all cations and anions passivation for stable perovskite solar cells with efficiency over 23%. Nano-Micro Lett. 2021, 13, 169. [Google Scholar] [CrossRef]
  4. Hu, Y.Q.; Shan, Y.S.; Yu, Z.L.; Sui, H.J.; Qiu, T.; Zhang, S.F.; Ruan, W.; Xu, Q.F.; Jiao, M.M.; Wang, D.H.; et al. Incorporation of gamma-aminobutyric acid and cesium cations to formamidinium lead halide perovskites for highly efficient solar cells. J. Energy Chem. 2022, 64, 561–567. [Google Scholar] [CrossRef]
  5. Rasool, S.; Hoang, Q.V.; Van Vu, D.; Song, C.E.; Lee, H.K.; Lee, S.K.; Lee, J.C.; Moon, S.J.; Shin, W.S. High-efficiency single and tandem fullerene solar cells with asymmetric monofluorinated diketopyrrolopyrrole-based polymer. J. Energy Chem. 2022, 64, 236–245. [Google Scholar] [CrossRef]
  6. Liu, W.S.; Huang, C.S.; Chen, S.Y.; Lee, M.Y.; Kuo, H.C. Investigation of Cu2ZnSnS4 thin film with preannealing process and ZnS buffer layer prepared by magnetron sputtering deposition. J. Alloy. Compd. 2021, 884, 161015. [Google Scholar] [CrossRef]
  7. Zhang, H.Y.; Wei, Z.; Li, P.F.; Tang, Y.Y.; Xiong, R.G.J.A.C.I.E. The narrowest band gap ever observed in molecular ferroelectrics: Hexane-1,6-diammonium pentaiodobismuth(III). Angew. Chem. Int. Ed. 2018, 57, 526. [Google Scholar] [CrossRef] [PubMed]
  8. Fabian, D.M.; Ardo, S. Hybrid organic–inorganic solar cells based on bismuth iodide and 1,6-hexanediammonium dication. J. Mater. Chem. A 2016, 4, 6837–6841. [Google Scholar] [CrossRef]
  9. Liu, X.Y.; Zhang, G.H.; Zhu, M.J.; Chen, W.B.; Zou, Q.; Zeng, T. Polarization-enhanced photoelectric performance in a molecular ferroelectric hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5)-based solar device. RSC Adv. 2020, 10, 1198–1203. [Google Scholar] [CrossRef] [Green Version]
  10. Jiang, Q.; Zhang, X.W.; You, J.B. SnO2: A wonderful electron transport layer for perovskite solar cells. Small 2018, 14, 1801154. [Google Scholar] [CrossRef]
  11. Chen, Y.C.; Meng, Q.; Zhang, L.R.; Han, C.B.; Gao, H.L.; Zhang, Y.Z.; Yan, H. SnO2-based electron transporting layer materials for perovskite solar cells: A review of recent progress. J. Energy Chem. 2019, 35, 144–167. [Google Scholar] [CrossRef] [Green Version]
  12. Nam, M.; Huh, J.Y.; Park, Y.; Hong, Y.C.; Ko, D.H. Interfacial modification using hydrogenated TiO2 electron-selective layers for high-efficiency and light-soaking-free organic solar cells. Adv. Energy Mater. 2018, 8, 1703064. [Google Scholar] [CrossRef]
  13. Nam, M.; Park, J.; Lee, K.; Kim, S.W.; Ko, H.; Han, I.K.; Ko, D.H. A multifunctional fullerene interlayer in colloidal quantum dot-based hybrid solar cells. J. Mater. Chem. A 2015, 3, 10585–10591. [Google Scholar] [CrossRef]
  14. Ke, W.J.; Fang, G.J.; Liu, Q.; Xiong, L.B.; Qin, P.L.; Tao, H.; Wang, J.; Lei, H.W.; Li, B.R.; Wan, J.W.; et al. Low-temperature solution-processed tin oxide as an alternative electron transporting layer for efficient perovskite solar cells. J. Am. Chem. Soc. 2015, 137, 6730–6733. [Google Scholar] [CrossRef]
  15. Yun, A.J.; Kim, J.; Hwang, T.; Park, B. Origins of efficient perovskite solar cells with low-temperature processed SnO2 electron transport layer. ACS Appl. Energy Mater. 2019, 2, 3554–3560. [Google Scholar] [CrossRef]
  16. Liu, X.; Tsai, K.W.; Zhu, Z.; Sun, Y.; Chueh, C.C.; Jen, A.K.Y. A Low-temperature, solution processable tin oxide electron-transporting layer prepared by the dual-fuel combustion method for efficient perovskite solar cells. Adv. Mater. Interfaces 2016, 3, 1600122. [Google Scholar] [CrossRef]
  17. Jia, J.B.; Dong, J.; Wu, J.H.; Wei, H.M.; Cao, B.Q. Combustion procedure deposited SnO2 electron transport layers for high efficient perovskite solar cells. J. Alloy. Compd. 2020, 844, 156032. [Google Scholar] [CrossRef]
  18. Bai, G.F.; Wu, Z.L.; Li, J.; Bu, T.L.; Li, W.N.; Li, W.; Huang, F.Z.; Zhang, Q.; Cheng, Y.B.; Zhong, J. High performance perovskite sub-module with sputtered SnO2 electron transport layer. Sol. Energy 2019, 183, 306–314. [Google Scholar] [CrossRef]
  19. Xu, X.X.; Xu, Z.; Tang, J.; Zhang, X.Z.; Zhang, L.; Wu, J.H.; Lan, Z. High-performance planar perovskite solar cells based on low-temperature solution-processed well-crystalline SnO2 nanorods electron-transporting layers. Chem. Eng. J. 2018, 351, 391–398. [Google Scholar] [CrossRef]
  20. Saeed, M.A.; Kim, S.H.; Baek, K.; Hyun, J.K.; Lee, S.Y.; Shim, J.W. PEDOT:PSS: CuNW-based transparent composite electrodes for high-performance and flexible organic photovoltaics under indoor lighting. Appl. Surf. Sci. 2021, 567, 150852. [Google Scholar] [CrossRef]
  21. Lee, J.H.; You, Y.J.; Saeed, M.A.; Kim, S.H.; Choi, S.H.; Kim, S.; Lee, S.Y.; Park, J.S.; Shim, J.W. Undoped tin dioxide transparent electrodes for efficient and cost-effective indoor organic photovoltaics (SnO2 electrode for indoor organic photovoltaics). NPG Asia Mater. 2021, 13, 43. [Google Scholar] [CrossRef]
  22. You, Y.J.; Saeed, M.A.; Shafian, S.; Kim, J.; Kim, S.H.; Kim, S.H.; Kim, K.; Shim, J.W. Energy recycling under ambient illumination for internet-of-things using metal/oxide/metal-based colorful organic photovoltaics. Nanotechnology 2021, 32, 465401. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Scanning electron microscopy of HDA-BiI5 thin films on electron transport layers prepared with different dilution ratios of SnO2 and H2O: (a) SnO2:H2O = 3:6, (b) SnO2:H2O = 3:8, (c) SnO2:H2O = 3:10, (d) SnO2:H2O = 3:12, (e) SnO2:H2O = 3:14.
Figure 1. Scanning electron microscopy of HDA-BiI5 thin films on electron transport layers prepared with different dilution ratios of SnO2 and H2O: (a) SnO2:H2O = 3:6, (b) SnO2:H2O = 3:8, (c) SnO2:H2O = 3:10, (d) SnO2:H2O = 3:12, (e) SnO2:H2O = 3:14.
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Figure 2. XRD patterns of HDA-BiI5 thin films deposited on “Glass/ITO/SnO2” substrates, where the SnO2 layers are prepared with different dilution ratios.
Figure 2. XRD patterns of HDA-BiI5 thin films deposited on “Glass/ITO/SnO2” substrates, where the SnO2 layers are prepared with different dilution ratios.
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Figure 3. EDS patterns of HDA-BiI5 thin films on Glass/ITO/SnO2 substrates at SnO2:H2O = 3:8 dilution ratio.
Figure 3. EDS patterns of HDA-BiI5 thin films on Glass/ITO/SnO2 substrates at SnO2:H2O = 3:8 dilution ratio.
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Figure 4. Ultraviolet-visible (UV-vis) absorption spectra of HDA-BiI5 films prepared on SnO2 layer prepared at five dilution ratios (inset: Tauc plot).
Figure 4. Ultraviolet-visible (UV-vis) absorption spectra of HDA-BiI5 films prepared on SnO2 layer prepared at five dilution ratios (inset: Tauc plot).
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Figure 5. Ultraviolet photoemission spectra of HDA-BiI5 films.
Figure 5. Ultraviolet photoemission spectra of HDA-BiI5 films.
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Figure 6. Photoluminescence spectra of HDA-BiI5 films on glass/ITO/SnO2 substrates at five SnO2 to H2O dilution ratios.
Figure 6. Photoluminescence spectra of HDA-BiI5 films on glass/ITO/SnO2 substrates at five SnO2 to H2O dilution ratios.
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Figure 7. Forward scanning J-V curve of photovoltaic devices with HDA-BiI5 as the light absorption layer, where the ETL is prepared at different dilution ratios.
Figure 7. Forward scanning J-V curve of photovoltaic devices with HDA-BiI5 as the light absorption layer, where the ETL is prepared at different dilution ratios.
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Figure 8. Distribution of performance parameters of five HDA-BiI5-based solar cells prepared with SnO2:H2O = 3:8.
Figure 8. Distribution of performance parameters of five HDA-BiI5-based solar cells prepared with SnO2:H2O = 3:8.
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Table 1. Photovoltaic performance parameters of solar cells fabricated with different dilution ratio of SnO2 to H2O.
Table 1. Photovoltaic performance parameters of solar cells fabricated with different dilution ratio of SnO2 to H2O.
SnO2:H2OPCE (%)Voc (V)Jsc (μA/cm2)FF (%)
3:60.00020.0415.0230.52
3:80.00240.3023.0334.82
3:100.00130.1819.4037.26
3:120.00080.1419.8430.46
3:140.00010.0313.4432.01
Table 2. Photovoltaic parameters for the five devices fabricated at 3:8 dilution ratios.
Table 2. Photovoltaic parameters for the five devices fabricated at 3:8 dilution ratios.
PCE (%)Voc (V)Jsc (μA/cm2)FF (%)
0.00240.323.0334.82
0.00210.288921.233.8468
0.00230.439518.528.6934
0.0020.440717.725.4019
0.00220.324221.830.6429
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Li, X.; Zou, X.; Zhang, C.; Cheng, J.; Li, G.; Wang, Y.; Wang, X.; Song, K.; Ren, B.; Li, J. Investigation on Film Quality and Photophysical Properties of Narrow Bandgap Molecular Semiconductor Thin Film and Its Solar Cell Application. Coatings 2021, 11, 1300. https://doi.org/10.3390/coatings11111300

AMA Style

Li X, Zou X, Zhang C, Cheng J, Li G, Wang Y, Wang X, Song K, Ren B, Li J. Investigation on Film Quality and Photophysical Properties of Narrow Bandgap Molecular Semiconductor Thin Film and Its Solar Cell Application. Coatings. 2021; 11(11):1300. https://doi.org/10.3390/coatings11111300

Chicago/Turabian Style

Li, Xiaotong, Xiaoping Zou, Chunqian Zhang, Jin Cheng, Guangdong Li, Yifei Wang, Xiaolan Wang, Keke Song, Baokai Ren, and Junming Li. 2021. "Investigation on Film Quality and Photophysical Properties of Narrow Bandgap Molecular Semiconductor Thin Film and Its Solar Cell Application" Coatings 11, no. 11: 1300. https://doi.org/10.3390/coatings11111300

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