Thin-film solar cells will become a significant renewable resource for our sustainable energy supply in the near future. These solar cells offer the most promising options for substantially reducing the cost of photovoltaic systems and allow high market penetration of solar electricity.
Thin-film solar cells are the new generation of solar cells that contain multiple thin film layers of photovoltaic materials. They are also known as thin-film photovoltaic cells (TFPV). A thin semiconductor device deposited on a glass or plastic substrate creates thin-film solar modules. The thicknesses of thin film layers are less as compared to PN junction solar cells.
Types of Thin Films in Solar Cell
The first thin-film photovoltaic technology to be commercialized was the amorphous silicon, which was used to power small electronic devices such as calculators. This was extended to larger modules capable of a broader range of applications. Many different materials and components contribute to the makeup of a thin film solar cell. This part briefly explains the types of thin film solar cell.
Amorphous-Silicon Thin Film Solar Cell
The amorphous silicon is widely accepted as a thin-film solar cell material because it is abundant, nontoxic, low-temperature processing, low-cost substrate, and capacity for large area deposition. One of the attractive features of α-Si is that it is a direct band gap material, which allows a significant fraction of sunlight to be absorbed within a thin layer of a few micrometers.
Most types of amorphous silicon solar cells are in superstrate configuration, which means that the light enters the solar cell through the supporting substrate. This configuration requires a highly transparent substrate material and the presence of a transparent conductive oxide (TCO) between the substrate and the active layer. These cells are also called p-i-n solar cells, referring to the sequence in which the different layers are deposited. The other option is to make n-i-p solar cells, which allows the wider variety of materials.
Chalcopyrite Based Thin-Film Solar Cell
Chalcopyrite based solar modules combine the advantages of thin film technology with the efficiency and stability of conventional crystalline silicon cells. It is therefore believed that chalcopyrite based modules can take up a large part of the photovoltaic market growth once true mass production is started.
Chalcopyrites are compounds based on the use of elements from groups I, III and VI of the periodic table and include copper indium diselenide (CuInSe2 ), copper gallium indium diselenide (CuGa1-xInxSe2 ) and copper indium disulfide (CuInS2 ). It has obtained efficiency levels as high as 20.3%.
Cadmium Telluride (CdTe) Thin Film Solar Cell
CdTe photovoltaic cells are the second most common solar cell technology in the world marketplace after crystalline silicon, currently representing 5% of the world market. CdTe thinfilm solar cells can be manufactured quickly and inexpensively, providing a lower-cost alternative to conventional silicon-based technologies.
The most common CdTe solar cells consist of a simple p-n heterojunction structure containing a p-doped CdTe layer matched with an n-doped cadmium sulfide (CdS) layer, which acts as a window layer. This structure is similar to the heterojunction in CIGS cells.
Gallium Arsenide-Based Thin Film Solar Cell
Gallium arsenide (GaAs) is one of the most commonly used III-V semiconductor compounds for photovoltaic applications. This can be accredited to its high electron mobility, its direct bandgap, and its well-handled growth mechanisms. GaAs has potential advantages such as low-temperature coefficient, good low light performance, and highest efficiency (28.8%).
Sources and Further Reading
1. Minnaert, B. ‘Thin Film Solar Cells’ : An Overview’, pp. 1–40.
2. Evaluation, T. (2000) ‘ThinFilm Solar Cells Technology Evaluation and Perspectives Acknowledgement / Preface’, pp. 1–58.
4. Chopra, KL, Paulson, PD and Dutta, V. (2004) ‘ThinFilm Solar Cells: An Overview’, 92(December 2003), pp. 69–92. doi: 10.1002/pip.541.