Low-cost Ⅲ-Ⅳ solar cells fabricated using hydride vapor phase epitaxy (HVPE) and smart stack technology

Multijunction SCs featuring multiple combined cells are extremely efficient, but they have not been widely adopted due to their manufacturing costs. We have been working on the epitaxial growth technology known as HVPE (hydride vapor phase epitaxy) which can grow materials at a cost of around a tenth of previous methods, and smart stack technology which is a low-cost bonding technique to use low-cost bottom cells such as Si or CIGS. Our target is 35% for conversion efficiency and ¥200/W for the fabrication cost. We will be able to mount these SCs on unmanned aerial vehicles and cars.

 We have achieved world record conversion efficiencies of 28.3% for HVPE grown SCs, and 28.1% for CIGS based 3-junction SCs fabricated using smart stack technology.

Development of high-efficiency and low-cost crystalline Si solar cells, Si-based multijunction solar cells, and advanced Si cell/module technologies for novel applications. 

In Si solar cells, which are the most widely used type of solar cell at present, it is desirable to develop low-cost materials and processes that enable high efficiency devices, as well as advanced cell/module technologies for novel applications.

So far, we have demonstrated 23.3% efficient ultrathin crystalline Si solar cells (~50 µm) whereby the overall thickness is as low as one third of that of a conventional solar cell. This would enable not only a significant reduction in Si consumption but also providing flexible solar cells that can fit onto curved surfaces such as the walls of a building. Furthermore, we have developed various types of novel Si solar cell architectures including a Si solar cell made by depositing thin and inexpensive materials such as titanium oxide (TiO_x) on Si, industrially feasible perovskite-Si tandem solar cells, strip-type Si solar cells and colored Si solar cell modules particularly aimed at building-integrated photovoltaic applications.

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