2, Toyota Motor Corporation, Shizuoka, , Japan
Development of high-efficiency solar cell modules and new application fields are very important for further development of photovoltaics (PV) and creation of new clean energy infra structure based on PV. Especially, technologies for making III-V compounds and silicon solar cells are currently the most mature among other materials because of their efficiency potential. As a result, combining these two materials is a promising way to further improve the efficiencies of state-of-the-art solar cells. Therefore, the Toyota Technological Institute recently launched significant research efforts in III-V on Si technologies based on its existing resources in both silicon and III-V technologies, ranging from crystal growth, material characterization, cell design, cell prototyping and module and system integration including automobile applications. Especially, III-V/Si tandem solar cells are expected to have great potential of various applications because of high efficiency with efficiencies of more than 35 % under 1-sun AM1.5 G, light weight and low cost potential.
This paper overviews efficiency potential and recent activities of various Si tandem solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, perovskite/Si and nanowire/Si tandem solar cells. Our analytical results for high-efficiency potential of various Si tandem solar cells analyzed by considering non-radiative recombination losses in Si tandem solar cells and materials show efficiency potentisal of more than 42% with 3-junction Si tandem solar cells and 35% with 2-junction Si tandem solar cells. Recent results for our 28.2 % efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si 3-junction solar cell are also presented. Approaches on automobile application by using III-V/Si tandem, partial concentration and static low concentration and so forth is also presented. The authours will also present our next targets such as 1) development of high-efficiency Si tandem solar cell modules with an efficiency of more than 30% under 1-sun, 2) improvements in large-area, high yield and highly reliable fabrication process, 3) development of application fields such as automobile applications.