CuInSe <sub>2</sub> and related I–III–VI <sub>2</sub> chalcopyrite compounds for photovoltaic application
Takahiro Wada
Abstract
Abstract CuInSe 2 and its related I–III–VI 2 chalcopyrite compounds have been studied for about 50 years for application to absorbers in polycrystalline thin-film solar cells. Several research groups developed Cu(Ga,In)Se 2 , Cu(Ga,In)(S,Se) 2 , and (Cu,Ag)(Ga,In)Se 2 solar cells with conversion efficiencies higher than 20%. The bandgap energies of these absorber materials in high-efficiency solar cells are less than 1.2 eV. Currently, wide bandgap chalcopyrite compounds, such as Ga-rich Cu(Ga,In)Se 2 , Cu(Ga,In)S 2 , and Ga-rich (Cu,Ag)(Ga,In)Se 2 , have gained attention as absorber materials for the top cells in tandem structure solar cells. However, the conversion efficiency of these wide bandgap solar cells cannot reach 20%. I–III–VI 2 chalcopyrite compounds are composed of three or more elements and their crystal and electronic structures are more complicated than III–V or II–VI compound semiconductors. In particular, phase diagrams containing the I–III–VI 2 chalcopyrite compounds are complex and vary greatly depending on the material systems. This article provides an overview of the current state of our materials science understanding of I–III–VI 2 chalcopyrite compounds. In particular, we discuss the differences between CuInSe 2 and the other chalcopyrite compounds based on their phase diagrams of I 2 VI–III 2 VI 3 pseudobinary systems such as Cu 2 Se–In 2 Se 3 .