Thin-film solar cells are manufactured by depositing one or more layers of photovoltaic materials onto substrates such as glass, plastic, or metal. Renowned for being lightweight, flexible, and versatile, they are exceptionally well-suited for a wide range of Building-Integrated Photovoltaics (BIPV) applications, especially on non-traditional or curved surfaces. While generally less efficient than crystalline silicon cells, thin-film technologies have improved between 2018 and 2023, offering efficiencies ranging from 10% to 20% depending on the material. They perform well in low-light and high-temperature conditions, making them ideal for building façades, windows, and other architectural elements where traditional solar panels may not be practical.
Cadmium Telluride (CdTe)
CdTe is one of the most widely used thin-film materials due to its cost-effectiveness and relatively straightforward production process. Recent advancements have pushed commercial CdTe module efficiencies to around 18%, with laboratory cells exceeding 22%. CdTe solar cells perform exceptionally well in higher temperatures and low-light conditions, which is advantageous for certain BIPV applications. Their improved performance ratio and lower temperature coefficient make them suitable for hot climates. Despite having slightly lower efficiencies compared to crystalline silicon, CdTe's lower manufacturing costs and excellent performance characteristics make it a popular choice for large-scale commercial installations, such as façades or flat roofs.
Copper Indium Gallium Selenide (CIGS)
CIGS technology is considered one of the most efficient thin-film options available. Between 2018 and 2023, laboratory efficiencies for CIGS cells have exceeded 23%, with commercial modules achieving efficiencies between 15% and 17%. CIGS cells offer high flexibility and can be produced in thin, lightweight layers, allowing integration into curved or flexible surfaces. They also exhibit strong performance in diverse weather conditions and have a good temperature coefficient, enhancing their suitability for BIPV applications like façades or rooftop installations. Although CIGS modules are generally more expensive to manufacture than CdTe, their higher efficiency and superior aesthetic integration often justify the cost for premium applications.
Amorphous Silicon (a-Si) and Microcrystalline Silicon (μc-Si)
Amorphous silicon (a-Si) is a non-crystalline form of silicon used in thin-film solar cells. While traditional a-Si cells have lower efficiencies, typically around 6% to 9%, advancements have led to the development of tandem or hybrid cells combining a-Si with microcrystalline silicon (μc-Si). These tandem cells have achieved efficiencies up to 12%. a-Si cells are very lightweight and flexible, making them useful for applications like windows or semi-transparent surfaces in BIPV. Their ability to function under low light and diffuse radiation conditions makes them suitable for areas with less direct sunlight. The low-cost production process of a-Si cells makes them attractive for smaller, less demanding solar applications in buildings.
Perovskite Solar Cells
An emerging thin-film technology, perovskite solar cells have garnered significant attention due to their rapidly increasing efficiencies and potential for low-cost production. Between 2018 and 2023, laboratory efficiencies for perovskite cells have surpassed 25%. While commercial availability is still limited due to challenges with long-term stability and scaling production, ongoing research is promising. Perovskite cells are lightweight and can be made semi-transparent, offering exciting possibilities for integration into windows and building façades in BIPV applications.
Organic Photovoltaics (OPV)
Organic photovoltaics represent another innovative thin-film technology using organic molecules or polymers to convert sunlight into electricity. OPVs are known for their flexibility, lightweight nature, and potential for low-cost, large-area production. As of 2023, OPVs have achieved efficiencies around 17% in laboratory settings. Their ability to be produced in various colors and degrees of transparency opens new aesthetic possibilities for BIPV, such as decorative façades and tinted windows. However, OPVs currently face challenges related to longevity and large-scale manufacturing.
Advantages of Thin-Film Technologies in BIPV
Flexibility and Lightweight: Thin-film modules can be manufactured on flexible substrates, allowing them to conform to curved surfaces and be integrated into building materials like roofing membranes or façade elements.
Aesthetic Integration: Thin-film solar cells can offer a uniform appearance and can be produced in different colors and levels of transparency, enhancing architectural design possibilities.
Performance in Diffuse Light: These technologies generally perform better in low-light conditions and are less sensitive to shading, making them suitable for urban environments where sunlight may be obstructed.
Temperature Coefficient: Thin-film modules often have a lower temperature coefficient, meaning their performance degrades less at higher temperatures compared to crystalline silicon modules.
