Modeling and design of III-V heterojunction solar cells for enhanced performance

Heterojunctions can increase the efficiency of solar cell devices rela-tive to homojunctions, but there is a large parameter space with sig-nificant tradeoffs that must be considered. Here, we present an experimental and computational study of III-V heterojunction solar cells and show how the emitter doping, emitter band gap, and het-eroband offsets impact device efficiency. Efficiency is maximized by pushing the junction depletion region into the wider band gap ma-terial while minimizing the effects of heteroband offsets through optimized choice of emitter band gap, emitter electron affinity, and/or emitter doping density. We use these results to guide optimization of devices grown by halide vapor phase epitaxy, achieving 27% efficiency in a GaAs/GaInPAs heterojunction device. We also show that heterojunctions yield proportionally larger effi-ciency improvements in lower-quality materials. Although the modeling was developed and validated using III-V materials, the re-sults are theoretically applicable to materials systems outside III-Vs.