Thin-Film Solar Cells for Building-Integrated Photovoltaic (BIPV) Systems

Abstract

The global temperature increase has posed urgent challenges, with buildings accountable for as much as 40% of CO₂ emissions, and their decarbonization is critical to meet the net-zero target by 2050. Solar photovoltaics present a promising trajectory, especially through building-integrated photovoltaics (BIPVs), where thin-film technologies can be used to replace traditional building materials. This article critically examined the development of thin-film solar cells for BIPVs, including their working mechanisms, material structures, and efficiency improvements in various generations. The discussion underscored that thin-film technologies, including CdTe and CIGS, had noticeably shorter energy payback times between 0.8 and 1.5 years compared to crystalline silicon modules that took 2 to 3 years, thus promising quicker recovery of energy and higher sustainability values. Whereas certain materials posed toxicity and environmental concerns, these were discovered to be surmountable through sound material selection and manufacturing innovation. The conclusions highlighted that the integration of lower material usage, high efficiency potential, and better energy payback performance placed thin-film BIPVs as an extremely viable option for mitigating lifecycle emissions. In summary, the review emphasized the critical role of thin-film solar technologies in making possible the large-scale implementation of BIPVs to drive the world toward net-zero emissions at a faster pace.

1. Introduction

The European Union, the United States, and other advanced countries have pushed for sustainable building construction and design in order to meet the net-zero emission objective by 2050 [1]. Building energy consumption is one of the most complex areas of the energy sector, as it depends on climate, building design, materials, technologies, and occupant behavior. With energy needs ranging from heating and cooling to lighting and appliances, buildings account for 30–40% of global energy use and nearly one-third of CO₂ emissions [2]. Reducing this demand is crucial for achieving sustainability goals, directly supporting SDG 7 (Affordable and Clean Energy), SDG 11 (Sustainable Cities and Communities), and SDG 13 (Climate Action). While solutions like energy-efficient designs, retrofits, smart systems, and renewable integration exist, implementation remains challenging due to high costs, policy gaps, and diverse user needs [3]. According to a report by the International Energy Agency (IEA) and UN Environment, building CO₂ emissions account for 39% of worldwide CO₂ emissions [4]. BIPV (Building-Integrated Photovoltaics) is one of the most effective approaches to address this problem, since it not only generates electricity for the building, but also provides shade, thermal insulation, reduced energy losses, an attractive appearance, and natural lighting [5,6]. The revolutionary notion of incorporating solar cells into the framework of a building can reduce material costs in new constructions by replacing traditional materials, and they can be retrofitted into older buildings [7]. Although the types of solar cells to be incorporated vary considerably depending on their structural and technological specifications, BIPVs may be used to replace roofs, facades, tiles, windows, walls, curtains, and carpets. Thin-film solar cells (TFSCs) are the market leader in BIPVs, with materials such as copper indium gallium selenide (CIGS), cadmium telluride (CdTe), amorphous silicon (a-Si), and others being utilized in PV cells [8]. Thin-film cells may be used to replace traditional construction materials and can also be used as a building envelope and power generator [9]. These BIPVs are superior to standard Building Applied Photovoltaics (BAPV) as they do not require a specific roof or ground installation and may be substituted by structural design, saving money on mounting materials, brackets, and rails, as well as not overloading the roof [10]. Due to its structural flexibility, extensive installation techniques, cost efficiency, esthetics, strong resilience to deterioration, lower thermal losses, lighter weight, and transparency ability (up to some extent), TFSCs have surpassed crystalline cells in BIPV applications [11]. Since TFSCs, particularly CdTe and CIGS, have been shown to be less temperature sensitive, they may be used in extremely hot areas [12]. The global rollout of thin-film building-integrated photovoltaics (BIPV) has really picked up speed in recent years, thanks to their perfect fit for façades, skylights, and semi-transparent glazing [13]. Thin-film technologies, mainly amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS), made up about 3% of global PV installations from 2015 to 2023, which translates to roughly 42 GW of total capacity across various applications [14]. However, BIPV is still a small slice of this pie: the global BIPV market was valued at around USD 24 billion in 2023 and is expected to grow quickly at double-digit rates, with thin-film leading the way in installed volume for façade and glazing uses [15]. Market reports and IEA-PVPS assessments show that thin-film modules are becoming the go-to choice in BIPV because of their lightweight design, flexibility, and superior low-light performance compared to crystalline silicon. The current literature and industry estimates suggest that the total installed capacity of thin-film BIPV worldwide is likely between 0.5 and 5 GW [16]. While this may seem small compared to the over 1.4 TW of global PV capacity, it highlights a growing trend towards integrated solar solutions [17]. Figure 1 shows the trend of thin-film technology compared with the already mature crystalline silicon, and the research in TFSC, especially in BIPV, has the potential to increase the overall production of thin film as the efficiency of CdTe has progressed rapidly to 22.1%.

This emerging deployment underscores the potential of thin-film BIPV in pushing forward net-zero building strategies and the pressing need for standardized international reporting to better capture its contributions. The major market share of thin-film solar cell technologies is 5.5%, and CdTe solar cell is the widely used TFSC, leading with the production of 6.1 (GWp), followed by CIGS with 1.5 (GWp), and a-Si with 0.2 (GWp) in 2020 [19]. The BIPV TFSC technology includes the BIPV window, which may be used to replace traditional window materials by sandwiching a layer of solar cells between two glass sheets [20]. The transparency of the window can be controlled along with shading and daylight elements. The electrical connections were hidden within the frame, giving it an attractive appearance. Another research shows that TFSC PV roofing laminates may be adhered to the roof structure with adhesive. It is simple to construct, and electrical wiring may be completed beneath the roof [21]. Because these TFSCs are made of plastic rather than glass, they will be weatherproof and walkable. The weight is too light, and it will not overburden the structure [22]. The main purpose of this research is to critically analyze the thin-film technology in building-integrated photovoltaics.

Figure 2 shows the hierarchy of solar technologies critically examined in this paper. The prime aim is to assess the practicality and real-world viability of some of the thin-film solar cells (TFSCs) used in building-integrated photovoltaic (BIPV) systems. Thin-film technologies currently account for approximately 2% of global photovoltaic production, with a 2023 annual output of around 12.5 GW, dominated mostly by cadmium telluride (CdTe) modules [23]. Second-generation TFSCs, cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and hydrogenated amorphous silicon (a-Si:H) are the most developed commercially and most used in BIPV applications [24]. Commercial module efficiencies are often between 9 and 19% for CdTe, 12–16% for CIGS, and 6–9% for a-Si, whereas laboratory reports stand at 21.0%, 23.4%, and 14.0%, respectively [25]. These technologies have been integrated into façades of buildings, rooftops, and glazing systems effectively because they are lightweight, flexible, and perform excellently under diffuse light. In contrast, third-generation solar cells like dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are quickly finding their place as possible substitutes for esthetic and semi-transparent BIPV applications [26]. DSSCs, with efficiencies in the reported range of 9–14%, present strengths in color tunability and indoor performance but still pose challenges in long-term stability and large-scale production [27]. Perovskite solar cells have shown impressive advances, with single-junction cells reaching over 26% efficiency and tandem perovskite–silicon configurations achieving over 34% efficiency under lab conditions, making them high-ranking contenders for future high-efficiency BIPV systems [28]. In spite of stability issues, moisture sensitivity, and lead toxicity concerns, ongoing development in encapsulation, large-scale fabrication, and compositional engineering is pushing these technologies toward commercialization. The estimated global BIPV market in 2024 is around USD 12.5 billion and is expected to expand significantly architectural applications increasingly require multifunctional and power-generating surfaces [29]. Thus, this review highlights not only second-generation TFSCs’ technological maturity, but also the auspicious research path of perovskite and DSSC technologies for large-scale BIPV deployment in the future. It also presents a focused and updated synthesis of thin-film photovoltaic technologies for Building-Integrated Photovoltaics, developing the literature through four unique contributions: First, this paper conducts a bibliometric analysis linked with a technology-centered review to illustrate thematic progress, but also patterns of collaboration and geographic research hubs in the field of thin-film BIPV. Second, it presents a comparative techno-environmental assessment (EPBT, LCOE, degradation behavior, and temperature sensitivity) for second- and third-generation thin-film technologies, complete with tables and figures synthesizing recent empirical evidence (2023–2025) and market data, thereby providing region-specific performance expectations for practitioners. Third, the review emphasizes practical issues in architectural integration, such as facade–glazing–roof window use cases, azimuth/tilt effects, and semi-transparent module trade-offs, and connects these to lifecycle and safety issues, such as toxicity, encapsulation, and recycling. This paper explicitly maps near-term R&D and policy gaps in the field-standardization for outdoor testing of BIPV facades, scale-up challenges for perovskites, circular–economy pathways for CdTe/CIGS, and opportunities from Industry 4.0 tools-before proposing a research agenda that bridges material innovation, system design, and digital optimization for market adoption. Together, these contributions are distinct from existing surveys, combining bibliometric evidence, up-to-date techno-economic synthesis, a focus on architectural applications, and a forward-looking roadmap for research and policy.

2. Methodology

This study conducts a bibliometric analysis as shown in Figure 3, enabling an in-depth examination of the global research landscape, collaboration networks, and scholarly contributions in the area of Building-Integrated Photovoltaics (BIPV), including its thin-film solar technologies.

Bibliometric data were collected from the Dimensions database because it guarantees comprehensive coverage of peer-reviewed journal articles, conference proceedings, book chapters, and patents, while also granting advanced citation tracking through which it provides a full overview of research productivity and international collaboration. Keywords like “Building Integrated Photovoltaic” and “BIPV” were used when searching through publication titles, abstracts, and keywords to develop a structured search strategy. To ensure quality, only English-language peer-reviewed journal articles and review papers were included, since they hold much greater value as carriers of information than other sources, supplying scientifically authentic academic output. The final dataset thus consisted of detailed bibliographic elements like names of authors, institutional affiliations, countries, publication years, journal sources, citation counts, and DOIs. The quality control process was followed by the identification and elimination of duplicate records before the actual analysis began.

The cleaned dataset was then analyzed using VOSviewer, version 1.6.20, to build bibliometric and visual network maps. Country-level co-authorship networks were developed using VOSviewer, in which each node represents a contributing country, and the node size represents the volume of publications from each country. The thickness of the connecting links represented the strength of international collaboration, based on the number of co-authored papers, and color-coded clusters represented regional or thematic research collaborations. Association strength normalization was used as the method of normalization to ensure balanced representation of countries, while all other default parameters for visualization were kept in order to be able to present all countries with the least amount of noise from those countries contributing minimally. This has indeed helped in mapping important global research hubs such as China, India, the USA, and the UK, and also regional clusters in Europe and Asia that present high collaboration intensity with rapid research growth concerning BIPV technologies.

The scope was further narrowed to enhance the methodological depth and specificity by focusing particularly on thin-film solar technologies within the broad BIPV context. This focus was selected because thin-film materials, including Cadmium Telluride (CdTe), copper indium gallium selenide (CIGS), and amorphous Silicon (a-Si), represent advantages concerning building integration: they are lightweight, flexible, and offer esthetic adaptability. Thin-film BIPV applications were identified and categorized by relevant building elements such as roof-integrated, façade-integrated, window-integrated, and skylight-integrated systems. Whereas roof applications are dominant, façade-integrated systems have greater importance due to the fact that the modules of these thin-film technology alternatives prove to be particularly suitable for vertical and curved surfaces, enabling seamless architectural integration without compromising building design. Additionally, it included environmental performance indicators like CO₂ emissions, embodied energy, energy payback time, recyclability, and lifecycle environmental impacts to give a more comprehensive evaluation of the sustainability of the thin-film technologies within BIPV systems.

This also presents a more refined methodological framework that can explore, in depth, the contribution of thin-film technologies to the advancement of BIPV beyond the traditional dominance of crystalline silicon systems. It also allows for the identification of emerging research trends, technological innovations, and collaboration patterns across different regions and building applications. Using a comprehensive bibliometric approach coupled with a technology focus, this study provides rich insights into the evolution, sustainability, and global diffusion of research concerning thin-film BIPV and forms a sound basis for future investigations and policy-oriented developments

3. Results

3.1. Amorphous Silicon (a-Si) Thin-Film Solar Cells in BIPV

Amorphous silicon (a-Si) solar cells were the earliest version of thin-film solar cells available in the market. In 1976, Carlson developed the world’s first amorphous silicon solar cells, which were commercially available in the market in 1981 [30]. Crystalline Silicon compounds have a fixed structure that is periodic and fairly regular. In such a silicon structure, every silicon atom is bonded with four neighboring silicon atoms through both short- and long-range bonds. The angle and the length of these bonds are also fixed and keep repeating themselves periodically. Unlike this typical behavior of crystalline silicon thin-film cells, the amorphous silicon thin-films have their bond angles and bond length distributed randomly throughout the silicon network [31]. The structure of an a-Si thin-film solar cell is, on average, less than 1 μm [32]. The structure of a single a-Si thin-film solar cell is shown in Figure 4.

A-Si thin-film solar cell fabrication is performed with the plasma-enhanced chemical vapor deposition (PE-CVD) technique in which hydrogen is used as an active material. So, the a-Si solar cells contain about 10% of hydrogen [34]. Due to this, these are sometimes referred to as hydrogenated amorphous silicon (a-Si:H). Although the word hydrogenated is usually eliminated for ease, as the non-hydrogenated a-Si thin-film solar cells do not have any useful features to be used in electronic devices. a-Si thin-film solar cells have a high absorption rate and can absorb a broad spectrum of light, including infrared and, in some cases, ultraviolet light [35]. It has a larger bandgap of 1.7 eV. About 90% of the upper bandgap photons can be absorbed only by a 300 nm film of a-Si solar cell, which makes these cells ideal for the PV panels, especially in the building-integrated PV systems [36].

A single-junction a-Si thin-film PV module goes through a significant decrease (10–30%) in its power output when it is exposed to sunlight during its initial phase of installation. This is called the Staebler–Wronski Effect (SWE) [37]. This can be avoided in case of a-Si thin-film PV modules if the module uses thinner junction layers to amplify the electric field strength around the module, which in turn decreases the solar cell efficiency. Conversion efficiency of a-Si thin-film solar cell is ~6.0–9.0%, and the conversion efficiency of a single-junction a-Si thin-film PV module is approximately 6.9% [38]. a-Si thin-film solar cell PV modules offer a remarkable use in building-integrated façades. They can be used as an envelope that, besides satisfying the building’s electricity requirements, serves overheating protection by being a solar shield and decreases heating and cooling loads by offering an added insulation layer. The mean module efficiency tends to be between 5 and 7% [39]. Previous studies reported [40] a-Si thin-film BIPV systems with four transparency levels and assessed their performance under various weather conditions. The most transparent module gave an efficiency of 2.93%, while the least transparent module gave 2.09%. The maximum efficiency was observed for the mid-level semi-transparent module with a module efficiency of 3.20% [40]. The research identified low correlation between module efficiency and levels of transparency in the case of a-Si thin-film-based BIPV systems. In another case, it was shown that a-Si thin-film transparent PV modules attained a conversion efficiency of 7% under standard test conditions for roof-integrated systems, with an average performance ratio of 81%, ranging between 60% and 97% over a period of 3.5 years of monitoring [41].

In addition to electricity generation, a-Si thin-film BIPV systems are extremely efficient in enhancing building energy performance overall. They are capable of significantly cutting the building’s space conditioning energy demand by 20–35% annually based on building orientation, insulation, and climate zone [42]. The semi-transparent character of a-Si modules enables improved daylighting, with consequent diminution of artificial lighting utilization by as much as 15–20%, a factor further decreasing operational energy use [43]. As façades, the modules are used as thermal barriers, reducing heat gain in summer and heat loss in winter, a direct impact on building thermal comfort and indoor environment quality. From the environmental point of view, the EPBT of the a-Si BIPV systems is relatively low, ranging from 1.5 to 2.5 years, much lower compared to traditional crystalline silicon PV systems, rendering them an environmentally friendly technology [44]

Based on price, a-Si modules have an economical Levelized Cost of Energy (LCOE), typically 0.08–0.12 USD/kWh, due to the low material consumption, uncomplicated deposition process, and integration feature that substitutes traditional façade or roofing materials [45]. This two-in-one capability powers generation and architectural purposes, lowering the total lifecycle cost of the building. In addition, the production energy demand and carbon footprint of a-Si modules are the lowest among the PV technologies, giving them a perfect fit for green building certifications like LEED and BREEAM. While a-Si thin-films have comparatively lower conversion efficiencies than CdTe or CIGS, their reliable operation under low-light, diffuse irradiance, and high-temperature conditions guarantees a steady energy yield, especially for city and tropical climates [46].

Worldwide, a-Si today is around 5–7% of the overall thin-film PV market, and much of its share is used for BIPV and small-scale distributed energy installations [47]. Demand is increasing incrementally as cities across the world adopt net-zero energy building (NZEB) regulations and more stringent building energy codes. Leading manufacturers are pushing the boundaries with multi-junction and tandem a-Si/µc-Si designs, which can reach 10–12% efficiency at the module level [48]. Design versatility and cosmetic integration possibilities coupled with these improvements make a-Si technology the most likely candidate for future urban energy generation. In addition, government policies supporting green architecture, urban decarbonization, and integration of renewables will continue to drive a-Si BIPV systems’ market share further. As the world places greater attention on sustainable building design, energy autonomy, and climate resilience, a-Si thin-film BIPV modules are set to be the game-changers in bringing the vision of UN SDG 7 (Affordable and Clean Energy), SDG 11 (Sustainable Cities and Communities), and SDG 13 (Climate Action) to life [49].

Azimuth angle is another major factor in characterizing the performance of a BIPV system. The variation in module’s power efficiency with azimuth angle for a roof-integrated a-Si thin-film transparent BIPV system is presented in

Table 1. Relative power performance of a-Si thin-film PV modules with varying azimuth angles [50].

Azimuth Angle (°)	Direction	Relative Power Performance (%)	Approx. Module Efficiency (%)	Representative Location (Latitude, Longitude)	Observation
0	South	100	2.5	New Delhi, India (28.6° N, 77.2° E)	Baseline orientation; optimal solar incidence on module surface
30	Southwest 30°	99	2.48	Tokyo, Japan (35.7° N, 139.7° E)	Slight decrease due to 30° deviation from south
60	Southwest 60°	93	2.33	Rome, Italy (41.9° N, 12.5° E)	Moderate efficiency loss as the module faces further from the optimal direction
90	West	83	2.08	Berlin, Germany (52.5° N, 13.4° E)	Significant reduction in performance for west-facing modules
270	East	78	1.95	Beijing, China (39.9° N, 116.4° E)	Lower efficiency due to reduced morning irradiance capture
300	Southeast 60°	88	2.20	Sydney, Australia (33.9° S, 151.2° E)	Moderate performance reduction for southeast 60° orientation
330	Southeast 30°	96	2.40	Los Angeles, USA (34.0° N, 118.2° W)	Slight reduction compared to south-facing orientation

Note: “Reference (100%)” indicates the baseline efficiency for south-facing modules. Actual module efficiency (e.g., 2–3% for a-Si) is applied to this orientation, and other directions are scaled relative to it.

.

Table 1 shows the relative power performance of a-Si thin-film-PV modules installed at different azimuth angles and points out orientation-dependent energy yield in BIPV systems. This table identifies how departures from the optimal south orientations affect energy conversion efficiency, an issue relevant for architects and energy planners when integrating photovoltaics into façades, skylights, or tilted roofs.

The table will enable the understanding of energy-yield variations across different building orientations by normalizing all the other orientations with respect to the south-facing module at 100%. Including actual module efficiencies, which stand between 2 and 3%, bridges theoretical performance and practical application, providing the readers with a clearer view of what power output is expected. Integrating geographical locations (latitude and longitude) of representative cities further helps contextualize these results, as solar geometry, altitude angle, and local climatic conditions substantially influence performance trends.

This addition contributes to the overall analysis by providing a geographically anchored, performance-based perspective on BIPV system design, thereby strengthening the practical relevance of the study. It supports the central argument that even modest azimuthal deviations can substantially affect thin-film module performance, especially for technologies like a-Si that already operate at lower efficiencies compared to crystalline silicon. The inclination and slope also impact the performance of the BIPV. For a transparent a-Si thin-film BIPV roof-integrated system, the effect of the changing power output with slope can be seen in Figure 5.

All factors such as orientation, slope, and geographical location have an impact on the module temperature, and temperature is strongly linked to the module’s performance. The output of an a-Si thin-film BIPV system is reduced by about 5% as the temperature rises. The average efficiency of a-Si-based BIPV systems that are commercially available is around 7% [52].

There is a lot of work just now aimed at the integration of a-Si thin-film modules into BIPV systems, which is leading to the creation of multi-MW installations. Nevertheless, the production cost of a-Si thin-film BIPV systems is relatively high, somewhere around USD 3/Wp more than other market alternatives [53]. The energy payback time (EPBT) is rather short, usually 1.5–2.5 years, and the Levelized Cost of Energy (LCOE) is between 0.08 and 0.12 USD/kWh, thus making them economically feasible during the radial life span [54].

3.2. Cadmium Telluride (CdTe) Thin-Film Solar Cells in BIPV

Cadmium telluride (CdTe) is the most commonly used thin-film technology across the globe. Cadmium telluride thin-film solar cells are made from thin layers of cadmium telluride used to absorb photons from sunlight and convert them into electricity. In this type of thin-film solar cells, the tin oxide (SnO₂) or cadmium stannous oxide (Cd₂SnO₄) is used to make the upper layer of the electrode, whereas copper-doped carbon is used to make the lower base electrode [55]. Cadmium sulfide (CdS) is placed between the space of the upper layer of the electrode and the base made from cadmium telluride. The structure of the CdTe thin-film solar cell is shown in Figure 6.

After the crystalline silicon, CdTe thin-film solar cells are the most used technology in BIPV throughout the world [57,58]. There are multiple reasons for the abundant use of CdTe thin-film solar cells. They have a wide band of solar spectrum (as shown in

Table 2. Degradation rates of CdTe modules under various tropical climatic conditions.

Location/Study	Average Temperature (°C)	Relative Humidity (%)	Annual Irradiance (kWh/m2)	Module Construction/ Encapsulation	Operational Duration (Years)	Observed Degradation Rate (%/Year)
India (Chandigarh) [63]	28	65	1850	Glass/Glass (EVA encapsulant)	5	0.6–0.8
Thailand [64]	30	75	1900	Glass/Backsheet	4	1.1–1.4
Brazil (Recife) [65]	29	80	2000	Glass/Backsheet (polymeric)	6	1.5–2.0
Malaysia (Kuala Lumpur) [66]	31	85	1950	Glass/Glass with edge sealant	5	0.5–0.7
Singapore [67]	30	80	2000	Glass/Backsheet (EVA)	8	0.9–1.2

) for absorption and can be manufactured easily and at a faster pace, thus providing a reduced cost of manufacturing as compared to the trivial crystalline silicon-based solar cells [59]. They have a bandgap of 1.45 eV. CdTe thin-film solar cell PV modules provide high efficiency and the lowest manufacturing cost as compared to other solar cells available in the market these days [60]. The highest conversion efficiency for them is 21.5% under laboratory conditions, which is significantly higher than other second-generation thin-film solar cells. A recent paper claims the laboratory efficiency to be 22.1% [61]. The efficiency of the modules available in the market keeps getting improved with chemical heat treatment over time. At present, the efficiency of CdTe thin-film PV modules is around 14.7% [62].

The degradation rates for CdTe modules can change quite a bit depending on the local climate and how the modules are constructed. Those with strong glass on both sides and better sealing at the edges show much lower breakdown over time, under 1% per year [68]. Polymeric back sheets tend to age faster in spots with lots of humidity. All of this strongly stresses the need to pick materials wisely and design the encapsulation right for keeping BIPV systems reliable in the long run, especially out in tropical or coastal places.

The module efficiency of CdTe thin-film solar cells varies with multiple factors. Firstly, the above-mentioned module efficiency is under laboratory conditions. Though the laboratory efficiency is also tested under controlled conditions, the absolute real-time efficiency of the module should be evaluated under actual outdoor operating conditions [69]. The performance degradation rate of 0.4% per year has been reported for the CdTe thin-film PV module after it is subjected to outdoor conditions [70]. Wu et al. (2001) experimentally present a degradation rate of 0.6% per year for a CdTe solar cell module after being subjected to outside conditions for five years, cited in [71]. In the tropical outdoor conditions, the degradation rate for these modules achieves as high as 2% per year after more than 3 years of outdoor environment conditions [72].

Some solar manufacturers claims the efficiency of CdTe thin-film solar cells in a BIPV system to be around 17.5% with a cell efficiency of 21% [73]. A previous study analyzed analyze the performance of a CdTe thin-film roof-integrated system with a capacity of 32.7 kWp. It uses the module with an efficiency of 9–11% [74]. Like the a-Si thin-film solar PV modules, CdTe thin-film modules’ performance is also greatly impacted by multiple factors such as temperature, slope, orientation, and geographical location, etc. As the day passes, the temperature of the modules in BIPV changes along with the angle of incidence. Hence, the performance of the system also changes. The performance ratio of the BIPV system also changes with time. For the CdTe thin-film BIPV system, it is reported to be between 75.55% to 76.94% [75].

Total energy produced by the CdTe thin-film BIPV system varies with the angle of inclination and the slope, like a-Si thin-film modules. This trend is shown in Figure 7. The difference is more evident for warmer and more humid areas.

Singh et al. (2020) show that different orientations of the BIPV system, such as façade, roof, or windows, significantly impact the power output, performance ratio, and the efficiency of the overall system, cited in [77]. Figure 7 shows the summed global irradiance received by different orientations of the CdTe thin-film BIPV system with similar module specifications. It is evident from Figure 8a that the roof-integrated system receives more sunlight and is translated into higher PR for a flat roof system as shown in Figure 8b.

One of the major concerns with CdTe thin-film solar cells is the toxic cadmium and the rarely available tellurium, which are used in the manufacturing process. This has caused uncertainty regarding CdTe thin-film modules to be a hazardous waste, which is now highly dependent on the type of construction of the module [79]. Also, the CdTe thin-film module efficiency is much lower than the cell efficiency. The instability caused by the cell degradation, as mentioned earlier, causes the obstacles in the way to achieve high current and high voltage [80].

3.3. Copper Indium (Gallium) Diselenide (CI(G)S) Thin-Film Solar Cells in BIPV

Copper Indium Selenide (CIS) is a semiconductor material (p-type) that is used as an absorbing layer for CIS-based thin-film solar cells. The CIS thin-film solar cells are fabricated using a thin layer of CulnSe2 [81]. A very common variation in CIS-based thin-film solar cells is copper indium gallium diselenide (CIGS) thin-film solar cells. The design for CIGS thin-film was initiated in 1981 after the development of CIS by Boeing company with 9.4% laboratory efficiency [82]. The structure for CIGS is shown in Figure 9.

The earlier version of CIGS, which was developed by the National Renewable Energy Laboratory (NREL), had a cell efficiency of 17%. In 2019, Solar Frontier experimented with CIGS with the highest efficiency of 23.35% [83]. The industrially produced have an efficiency of 7–16%. The bandgap of CIGS thin-film solar cells is 1.1–1.2 eV [84].

Figure 9. Structure of CIGS thin-film solar cell [85].

Figure 9. Structure of CIGS thin-film solar cell [85].

The design of CIGS in the CIS family has introduced the concept of flexible PVs in the building-integrated PV systems. The substrates made from polyimide have introduced flexibility in these modules [86]. The higher material flexibility, along with higher resistance in outdoor environments and against solar radiation intensity and high specific power, has made this class of thin-film PV modules very desirable for BIPV systems [87]. Some researchers presented the performance evaluation of a CIS thin-film BIPV system with the module efficiency of 10–12% [88]. The effect of the external parameters, such as temperature, slope, irradiance level, orientation, and location, etc., is the same in the case of the CIS thin-film BIPV system. The average performance ratio of the CIS thin-film BIPV system is 72.79% which is impacted slightly due to the seasonal effects [89]. The effect of different orientations on the performance ratio of the CIS BIPV system across various sites in India is shown in Figure 10. The difference in orientation is dictated mostly by the warmer and more humid site (Chennai).

Figure 10. Average yearly electricity generation of CIS-based PV systems under different configurations across six Indian climatic zones. Energy yield increases with higher solar irradiance, indicating strong climatic influence on CIS module performance [90].

Figure 10. Average yearly electricity generation of CIS-based PV systems under different configurations across six Indian climatic zones. Energy yield increases with higher solar irradiance, indicating strong climatic influence on CIS module performance [90].

CIGS thin-film BIPV systems present a better performance ratio due to the increased efficiency at the first time of use after installation. Higher efficiency and environmental resistance make CIGS thin-film solar cells essential for some BIPV applications. Recently, Dow Chemicals has introduced CIGS-based shingles for the latest BIPV system, which provides as much material strength as normal asphalt-based shingles, with the added benefits of the CIGS BIPV system and a life span of around 15 years [91].

The primary limiting factor in this case is the scarcity of iridium. Also, there are added health hazards from gallium, sulfur, and selenium. High variation in the physical properties, low open circuit voltage, and the design demand for higher bandgap alloys are also the other limitations associated with CIGS thin-film BIPV systems [92].

Today, the most common application of CIGS thin-film modules is in space applications, but these are becoming more popular in BIPV systems due to their high performance under lower solar irradiance levels. CIGS BIPV systems have the highest efficiency and are becoming more popular commercial thin-film solar panels [93]. Although CIGS do not occupy as much market among thin-film solar systems as CdTe, it still holds 2% of the total market, provided that the total share of the thin-film systems in the PV market is 10% [94].

3.4. Gallium Arsenide (GaAs) Thin Film Solar Cells in BIPV

Gallium Arsenide-based PV modules are also becoming popular as their direct bandgap matches the solar spectrum, allowing them to emit light efficiently. These types of cells also have a high absorption rate and very little energy loss. GaAs thin-film cells are primarily made from gallium and arsenic, as shown in Figure 11. This is also a very useful semiconductor material that has interesting applications in transistors and has a higher breakdown voltage [95].

The cell efficiency of GaAs thin-film solar cells is about 30.5% under laboratory conditions. Also, under some laboratory conditions, flexible thin films of GaAs have also been formed using the liftoff technique. Although the commercial production of such cells has not started yet [96].

Figure 11. GaAs Single-Junction Solar Cell [97].

Figure 11. GaAs Single-Junction Solar Cell [97].

There are many limitations associated with GaAs thin-film solar cells. Firstly, these cells are more expensive than the other thin-film solar cells. But still, these are widely used in spacecraft [98]. Secondly, there are health hazards associated with gallium which can result in skin diseases. Also, the other primary element, arsenic, has higher toxicity due to its carcinogenic properties. Unless the cost for the GaAs is reduced, its applications cannot be expanded beyond spacecrafts [99].

3.5. Third-Generation Thin-Film Solar Cells in BIPV

OSCs (organic solar cells) are organic semiconductors having a thickness of 100 nanometers. The power conversion efficiency of OSCs has been recorded as 18% [100]. Whereas they are linked with low cost, being lightweight, quickly produced, and ecologically beneficial as compared to the traditional Silicon cells. OSCs carry materials which have a substantially higher absorption coefficient than inorganic semiconducting materials [101]. The conductivity and average visible-light transmittance (AVT) of the top electrode might be adjusted by using the proper material and modifying the top electrode. Semi-transparent OSCs can be utilized to generate energy in structures designed in the form of windows and ceilings [102].

CZTS (copper zinc tin sulfide) cells as shown in Figure 12 are non-toxic and ecologically friendly solar cells manufactured from a quaternary semiconducting material employing thin-film solar technology. Despite constraints such as raw material shortages, the CIGS type has a high efficiency of greater than 20% [103].

CZTS solar cells are also utilized as absorbers, with two types of structure: stannite and kesterite. The second type has a lower level of toxicity and a higher number of components. Existing CZTS efficiency is ~7.5%, different research is being made as these cell materials are non-toxic, inexpensive, and manufacturing does not require a high amount of energy [105]. Currently, the roof installation/integration market for CZTS is being considered as it is flexible and less efficient [105].

DSSC (Dye-Sensitized Solar Cells) are thin-film solar cells (as shown in Figure 13) that employ a photosensitive dye to absorb light and produce electricity. DSSCs are noted for low production costs, flexibility, and good performance under diffuse light, which makes them ideal for indoor and building-integrated applications [106].

Power conversion efficiency (PCE) of DSSCs is as high as 12–13% in the laboratory setting, although commercial modules are generally 8–10% efficient [108]. They also have the benefit of being semi-transparent and could be used in windows, façades, and skylights like OSCs. DSSCs do have some drawbacks, such as long-term stability concerns and the employment of liquid electrolytes, which can lead to leakage or degradation over time [109].

Perovskite solar cells (PSCs) are a newly emerging family of photovoltaic devices (as shown in Figure 14) composed of organic–inorganic hybrid perovskite compounds, typically with the general formula ABX₃ (where A = cation, B = metal, X = halide) [110].

PSCs have drawn considerable interest owing to their high-power conversion efficiency, which has quickly escalated from ~3% to more than 26%, comparable to crystalline silicon solar cells [112]. They are also flexible, light in weight, and inexpensive to make, which makes them likely candidates for BIPV modules and flexible solar panels [113,114]. PSCs face challenges of long-term durability under heat, moisture, and UV radiation, and the use of lead compounds in most high-quality perovskites. Researchers are working on lead-free perovskites and encapsulation methods to overcome these challenges [115].

Table 3. A dedicated table summarizing the EPBT and Levelized Cost of Energy (LCOE) for thin-film BIPV technologies.

Technology	EPBT (Years)	LCOE (USD/kWh)	Geographic Context
a-Si (Amorphous Si) [116]	1.5–2.5	0.08–0.12	Europe (Germany, Spain)
CdTe (Cadmium Telluride) [117]	1.0–1.8	0.06–0.10	Tropical (India, Brazil, Malaysia)
CIGS/CIS [118]	1.5–2.0	0.05–0.09	Europe (Germany, Netherlands)
GaAs [119]	2.0–3.5	0.15–0.25	USA (Arizona, California)
OSCs (Organic) [120]	0.5–1.5	0.10–0.14	East Asia (Japan, South Korea)
CZTS (Cu2ZnSnS4) [121]	1.8–2.5	0.08–0.11	Europe (France)
DSSC (Dye-Sensitized) [122]	1.0–1.8	0.09–0.13	Europe (Italy, Sweden)
Perovskite [123]	0.3–0.8	0.05–0.09	Asia (China, Singapore)

presents a comparative assessment of energy payback time (EPBT) and Levelized Cost of Energy (LCOE) for different types of thin-film BIPV technologies. The results indicate that CdTe modules offer the shortest EPBT (1.0–1.8 years) and reasonably priced LCOE (0.06–0.10 USD/kWh), especially in tropical climate zones like India, Brazil, and Malaysia, which is due to their low embodied energy and high-temperature tolerance. CIGS modules experience somewhat longer EPBT (1.5–2.0 years) but also deliver reasonably priced LCOE (0.05–0.09 USD/kWh), while exhibiting excellent energy performance in temperate European climates. Although a-Si modules are environmentally friendly materials, they experience both longer EPBT (1.5–2.5 years) and higher LCOE (0.08–0.12 USD/kWh) because of their lower conversion efficiency. Emerging technologies, including perovskite and organic solar cells, show substantially reduced EPBT (<1 year) and potentially reasonable LCOE (<0.10 USD/kWh), especially in the laboratory prototype demonstrations, but stability and scale-up strategies remain important to address. Overall, for both tropical and temperate regions and for large-scale BIPV deployment, the techno-economic value provided by thin-film technologies appears to be more promising for both CdTe and CIGS at present.

The comparative assessment of different thin-film PV technologies like a-Si, CdTe, CIGS, GaAs, OSCs, CZTS, DSSC, and PSCs outlines that every technology has its own advantages in various respects, depending on the environmental context, the fabrication process, and integration flexibility. But to fully exploit their potential in BIPV systems, there is a pressing need to align material science and system design with the transformative principles of Industry 4.0. Modern digital technologies -AI, IoT, digital twins, and ML-based optimization are presently being sought in the design and operation of photovoltaic systems. For example, AI-driven modeling and predictive analytics can dynamically find optimum orientation, tilt angle, and module cleaning schedules from real climatic and irradiance data, which helps minimize degradation and optimizes the lifetime performance of thin-film modules. IoT-enabled smart sensors embedded in BIPV façades provide continuous monitoring of temperature, humidity, and voltage fluctuations; therefore, predictive maintenance and early fault detection may improve, reducing downtime and enhancing the consistency of energy yields. Moreover, the digital twin concept is being used more and more in simulating the thermal and electrical behavior of façade-integrated PV modules in order to virtually test materials like a-Si, CdTe, and CIGS under diverse building geometry and environmental conditions before physical installation. These linkages between physical and digital layers represent a paradigm shift in the assessment and improvement of BIPV performance, where data-driven decision-making blends conventional experimental and field studies to more accurate, more scalable, and more cost-effective deployment strategies.

4. Results and Perspective

From the Industry 4.0 point of view, the next generation of BIPV systems is targeted to become smart, adaptive, and interconnected energy infrastructures operating synergistically with building management systems. Due to CPS and blockchain-based energy management, the BIPV installation can share information directly with smart grids to allow P2P energy trading, demand-side management, and dynamic load balancing. As an illustration, real-time energy data from CdTe or CIGS façade modules can be integrated with AI-based control algorithms for the optimization of electricity generation and storage in a building’s microgrid, matching supply with occupation patterns and lighting demand. Additive manufacturing or 3D printing and robotic automation are also used in the revolutionary thin-film module fabrication process, mainly for flexible and perovskite-based modules. Such techniques have made mass customization of PV tiles and façades possible, with a gain in precision, less waste, and reduced production costs. Big data analytics will show, among others, the correlation of module degradation trends in various climatic zones-as can be seen in the results tables-to develop standardized reliability models that guide material selection and encapsulation strategies for specific geographies. In the broader context of sustainability, integration with smart city infrastructure creates pathways to Net-Zero Energy Buildings and carbon-neutral urban environments, which would support global decarbonization under UN SDGs 7, 11, and 13. The emerging convergence between photovoltaic innovation and digital intelligence stands to enhance not only the efficiency and safety but also the resilience of BIPV systems, accelerating the rate at which they will be adopted as core elements of intelligent, self-regulating urban ecosystems. The way forward definitely lies in integrating material and process innovations in thin-film PVs into the intelligent, interconnected architecture of Industry 4.0 to form a strong foundation for the next era in energy-positive building design.

Thin-film photovoltaic (TFPV) systems are promising candidates for building-integrated photovoltaic (BIPV) applications based on their adaptability to architectural surfaces, lightweight structures, and esthetic diversity. Also, they are less impacted by temperature changes, and they perform better under diffuse light, compared to conventional crystalline silicon-based systems [124]. Nonetheless, the performance is still mostly dependent on the quality of the material, design of the module, and environmental aspects such as irradiation and temperature. Gallium arsenide (GaAs) cells, for example, have the highest conversion efficiency under laboratory conditions, but the production cost and environmental aspects limit large-scale use in BIPV [125].

Roof-integrated thin-film modules generally have higher energy yield than façade-integrated systems due to better exposure to sunlight and optimal inclination angles.

Table 4. Cell and module efficiencies of thin-film solar cells in BIPV systems (updated using Martin Green, 2024) [126].

Technology	Cell Efficiency (%)	Module Efficiency (%)	Source/Developer	Temperature Coefficient (%/°C)
Crystalline Silicon (c-Si)	26.8 ± 0.4	22.8 ± 0.3	NREL	−0.35
Amorphous Silicon (a-Si)	10.2 ± 0.3	9.1	AIST	−0.18
Cadmium Telluride (CdTe)	21.1 ± 0.4	18.6 ± 0.5	First Solar	−0.25
Copper Indium Gallium Selenide (CIGS)	21.7 ± 0.5	19.2 ± 0.5	Solar Frontier	−0.30
Gallium Arsenide (GaAs)	28.8 ± 0.9	25.1 ± 0.8	Alta Devices	−0.25
Copper Zinc Tin Sulfide (CZTS)	10.0 ± 0.2	—	UNSW	−0.35
Dye-Sensitized Solar Cell (DSSC)	13.5 ± 0.3	10.5	EPFL	−0.45
Perovskite	27.3 ± 0.5	22.8 ± 0.4	NREL/KAUST	−0.20

compares efficiencies of various BIPV thin-film technologies at the cell and module level, and is based on data compiled from the most recent Solar Cell Efficiency Tables (Version 66), published by [126] in 2024.

According to [126], thin-film technologies such as CdTe and CIGS have developed significantly in efficiency and stability, closing the gap with crystalline silicon. Perovskite thin-film cells have achieved 27.3% certified cell efficiency, which is an indication of the rapid technological advancement that has happened in just one decade [127]. However, many technical issues related to stability, encapsulation, and environmental durability are still problematic for large-scale commercialization.

Nevertheless, the penetration of thin-film technology in the market is still limited, as it currently represents approximately 10% of the global PV market [128]. The leading technology in the thin-film category is CdTe, followed closely by CIGS and finally amorphous silicon. GaAs is also in the market, but its application is limited, and the cost is much higher.

Table 5. Global market share and average price range of thin-film solar technologies [129,130,131].

Technology	Market Share (2024)	Price Range ($/W)	Category
Crystalline Silicon (c-Si)	~91%	0.18–0.30	Module
Amorphous Silicon (a-Si)	2.0%	0.69	Module
Cadmium Telluride (CdTe)	5.1%	0.40	Module
CIGS	2.0%	0.60	Module
GaAs	<1%	50.0	Cell
Perovskite	<1%	0.25–0.35 (estimated)	Cell/Module

shows the market share and a price comparison.

CdTe thin-film technology will continue to service the thin-film BIPV market because it was developed with reliability in mind, is easily manufactured, and is cost-effective [132]. Due to its low cost per watt, CdTe is a great product for larger façade applications; however, perovskite PV modules are still working to commercialize from laboratory-scale production to pilot-scale production.

4.1. Health and Environmental Hazards of Thin-Film BIPV Systems

While thin-film solar cells have the potential for sustainability, hazardous materials are involved during manufacture and disposal. Thin-film technologies are reliant on rare and toxic elements, such as cadmium, tellurium, arsenic, indium, gallium, and selenium, unlike conventional silicon photovoltaics (PVs). The manufacturing process also generates large quantities of corrosive chemicals (hydrochloric acid, sulfuric acid, hydrogen fluoride, and nitric acid) and toxic gases (arsine, phosphine, silane, and hydrogen selenide) that would pose substantial occupational and environmental health and safety issues if not appropriately mitigated [133]. The hazard classifications for commonly used materials in PV manufacturing are provided in

Table 6. Health hazards of thin-film BIPV [133,134,135,136].

Material	Source	DOT Hazard Classification	Critical Health Effects
Arsenic	GaAs	Poison	Cancer, lung toxicity
Cadmium	CdTe, CdS	Poison	Kidney and bone damage
Indium	CIGS	Not regulated	Pulmonary fibrosis
Tellurium	CdTe	Not regulated	Cyanosis, liver effects
Hydrogen Fluoride	a-Si	Corrosive	Burns, respiratory hazard
Arsine	GaAs (CVD)	Highly toxic gas	Blood, kidney toxicity
Silane	a-Si deposition	Pyrophoric gas	Explosion hazard
Hydrogen Selenide	CIS	Highly toxic gas	Irritant, lung damage
Phosphine	a-Si dopant	Pyrophoric gas	Fire and irritation hazard

.

Recently, with the future increase in perovskite building-integrated photovoltaics (BIPVs), the presence of lead in the perovskite absorbers is rising in concern. The leakage of lead and other environmental hazards, from a damaged module unit or during the end-of-life phase of the modules, may be a larger environmental issue if lead is not contained. The research community is actively investigating lead-free perovskite substitutes (Sn-, Sb-, and Bi-related compounds) and encapsulation routes to stop lead migration [137]. Therefore, instead of solely focusing on innovation in green manufacturing processes and materials substitution, a safe recycling and disposal pathway for thin-film BIPV modules needs to be equally prioritized.

While thin-film photovoltaic technologies are based on CdTe and CIGS, which all contain toxic elements (Cd, Se, Pb), they are not highly restricted because they are made from chemically stable compounds and are coated with glass that keeps them contained. For instance, the leaching of Cd from CdTe modules is less than 0.01 mg/L (often lower), which is orders of magnitude less than the U.S. EPA toxicity criterion of 1 mg/L, indicating that there is little environmental concern during normal operation of the module [138]. Furthermore, over 90–95% of semiconductor material can typically be recovered and reused with existing recycling technologies, and the material utilization efficiency in the production process is frequently in excess of 95% reducing waste [139]. The manufacturing is performed in closed systems with continuous air filters and chemical recovery units that keep occupational exposure levels to cadmium (as air contamination) safely below the OSHA limit of 5 µg/m³ [140]. Upon the end-of-life cycle, regulated recycling practices, along with controlled encapsulation methods, guarantee that contaminating potential is negligible. Overall, thin-film PV technologies are deemed socially and environmentally acceptable under existing regulations, such as RoHS and REACH, even with hazardous elements in the manufacturing process, due to secure operational handling and minimal risk to environmental health and safety, as noted above [140].

4.2. Future Directions and Opportunities

The advancement of thin-film building-integrated photovoltaics (BIPV) systems will be predicated on the incorporation of new materials, sustainable design, and digital optimization technologies. For example, perovskite–silicon and perovskite-copper indium gallium diselenide (CIGS) tandem architectures achieved greater than 32% efficiency in laboratory settings (2024). The tandem architectures have the potential to deliver conversion efficiencies greater than the Shockley–Queisser limit, which generally regulates the efficiencies (<30%) of single-junction devices while maintaining the flexibility and semi-transparency of BIPV façades [141]. In addition, with the integration of artificial intelligence (AI)-based modeling and life cycle assessment (LCA), and a machine-learning-based apparatus for fault-ranking detection developed into smart façades, orientations, shading, and thermal management can be optimized as these systems function. Integration of Building Information Modelling (BIM) with diverse PV simulation tools, e.g., PVsyst, and SCAPS-1D, will enable architects to assess building performance as it reflects different climate zones and geometries [142]. Lastly, hydrogen-passivated thin-films and plasma-enhanced deposition methods have improved the stability of thin-films against moisture and ultraviolet (UV) exposure and have been identified as increasing the life span of solar modules beyond 25 years. Future research must also address the standardization of testing BIPV performance in façades, as the majority of testing is conducted on lab-scale or roof-integrated systems and does not occur under real-world conditions [143].

New environmentally friendly absorbing materials such as CZTSSe and carbon-based perovskites have the potential to be good substitutes for existing absorbing materials due to their low toxicity and abundance. In the context of buildings, combining these absorbers with phase change materials (PCMs) within a building envelope can provide improved thermal regulation as hybrid systems that produce electricity while enhancing building energy performance [144,145,146,147].

5. Conclusions

The thorough review highlights the importance of thin-film solar technologies to further the large-scale adoption of building-integrated photovoltaics (BIPVs) in achieving net-zero energy and carbon goals in the built environment. The review shows that in the second-generation thin-film solar cells, cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) provide the most promising performance envelope in efficiency, cost, and durability, with module efficiencies as high as 18–19% and low temperature coefficients that allow them to perform well in various climatic conditions. Amorphous silicon (a-Si) remains an excellent option for semi-transparent façades and roofs because of its low embodied energy, costs, and performance under diffuse irradiance. Although gallium arsenide (GaAs) has the highest conversion efficiencies, its high manufacturing cost, in combination with toxicity, makes it hard to scale in architectural applications.

Third-generation technologies such as dye-sensitized solar cells (DSSCs), organic solar cells (OSCs), and perovskite solar cells (PSCs) are emerging quickly as potential esthetic and multifunctional candidates for BIPV integration. Perovskite thin films in particular have made rapid advances with power conversion efficiencies above 27% and tunable optical transparency for semi-transparent façades and window-integrated photovoltaic systems.

Nevertheless, challenges of stability, moisture resistance, and lead toxicity continue to be challenges that inhibit their deployment, which also means more research and design on encapsulation, compositional engineering, and lead-free alternative solar materials will still be important. The threats to environmental conditions and to human health created by toxic and scarce elements like cadmium, tellurium, gallium, and selenium only emphasize the need for cleaner production practices, circular economy approaches, and other recycling systems. Green practices for manufacturing, along with non-toxic absorber materials like copper zinc tin sulfide (CZTS), could create a sustainable pathway for the next generation of thin-film BIPVs. In addition to these, integrating phase change materials (PCMs) and advanced coatings could improve thermal comfort and energy performance in buildings, thus enabling a holistic approach to energy-positive architecture.

From a techno-economic viewpoint, thin-film BIPV modules also indicate shorter payback times (0.8–2.5 years) and competitive Levelized Cost of Energy (0.08–0.12 USD/kWh), which again reinforces their potential as sustainable, cost-competitive energy options. Coupling reduced material consumption with lightweight design, along with esthetic options, contributes to the potential of thin-film technologies as a decarbonizing transformation of buildings.

The potential of the market is further strengthened by the rapid urbanization trends and by tighter global standards for buildings’ energy efficiency, which is reigniting the market demand for multifunctional building envelopes that will both produce clean electricity and enhance the thermal performance of buildings. Future research should focus on hybrid perovskite–silicon and perovskite CIGS tandem architectures, AI-optimized facade designs, and consensus on standardized outdoor testing protocols to demonstrably prove longevity. The combination of digital tools, such as Building Information Modelling (BIM), SCAPS-1D, and PVsyst, can facilitate design optimization and expedite market adoption of thin-film BIPVs. In summary, thin-film BIPVs will create a transformative effect on the urban energy landscape by turning buildings from passive consumers of energy to active generators of energy, therefore helping to advance global progress toward sustainable cities and a carbon-neutral future.