III-V Compound heterojunction solar cells

Silicon has been used for most solar cell applications in the past, owing to the availability of the necessary technology. But from a fundamental materials standpoint, Si is a poor choice. It has a lower-than-optimum bandgap for highest efficiency, a low optical absorption coefficient requiring long lifetime material which is sensitive to radiation damage, and no material with which it forms a high quality heterojunction. III-V semiconductors have properties which avoid these problems and permit greatly improved solar cell performance. High quality heterojunctions have been demonstrated in several III-V systems including In1-xGaxAS1-yPy(1) and Al1-xGaxAs1-yPy(2). Direct bangap materials with hlgh optical absorption coefficients are available with bandgaps from 0.4 to 2.1 eV. These advantages have long been known, but the AlGaAs/GaAs heterojunction cell was the first to demonstrate them experimentally.