The global concern about climate change is a major one. It has been proven that fossil fuels are harmful to the environment and not sustainable. Solar cells are one of the most popular options for clean energy. Solar cells are efficient, but researchers also want to develop solar cells that can be lightweight, cost-effective, and flexible. The manufacturing process has been a major environmental problem due to the use of toxic materials as well as the generation of industrial waste.
Copper indium gallium selenide (CIGSe), for instance, is a thin film solar cell that has many advantages over traditional silicon cells. Thin-film solar cell are 100 times thinner and easier to mount on roofs or vehicles. CIGSe can also absorb light better than other photovoltaic materials like amorphous silica, cadmium telluride, and organics. It can also be made into thinner films. They do contain a buffer layer made of cadmium-sulfide which is extremely toxic and can cause cancer. It is therefore crucial to find non-toxic materials for large-scale production of CIGSe panels.
Professors Takashi Minemoto and Jakapan Chantana, both from Ritsumeikan University in Japan, felt that removing cadmium solar cells was just as important as creating an efficient and cost-effective manufacturing process. A research team that was led by them devised a strategy to address these issues. It involved replacing the traditional cadmium-sulfide buffer with a native buffer layer. This buffer was formed by oxidizing Cu(In.Ga)(Se) CIGSSe surface with an air-annealing process.
Although attempts to oxidize CIGSSe have been attempted before, it can take months for the surface to oxidize. The new method however reduced the time it takes to oxidize the CIGSSe layer. This allows for faster manufacturing using a “roll-to–roll” process. A CIGSSe layer is first deposited on a flexible, stainless-steel substrate. After the deposition, the surface of the CIGSSe is oxidized to create native buffer layers of In x (O,S), and. The researchers created a CIGSSe solar panel with 16.7% energy conversion efficiency after six hours of oxidation at 130°C.
“Prof. Minemoto says that we have discovered for the first-time that CIGSSe’s surface is oxidized by an optimized air-annealing procedure leads to a significant increase in energy conversion efficiency.”
The solar cells are eco-friendly, even though their efficiency is lower than conventional solar cells which typically exceed 20%. “In the traditional process, cadmium was deposited on the CIGSSe layers via a chemical bath process. Professor Chantana explains that by eliminating this step, the manufacturing process is completely dry and generates less waste. The process is also cost-effective.
Solar energy must be more economically efficient and environmentally friendly in order to become a viable source for clean energy. Professor Minemoto concludes that the method we developed can be scaled up to large-scale manufacturing applications. This is what is needed to make solar energy a viable source of clean energy not only in Japan, but around the globe.
