Electron-Selective Contact for GaAs Solar Cells
Vidur Raj, Tuomas Haggrén, Julie Tournet, Hark Hoe Tan, C. Jagadish
Abstract
In recent years, carrier-selective contacts have emerged as an efficient alternative to the conventional doped p–n or p–i–n homojunction for charge carrier separation in high-performance solar cells. However, so far, there has been no development in carrier-selective contacts for GaAs solar cells. This paper proposes an alternative device structure and reports an 18.5% efficient single-junction GaAs solar cell using zinc oxide (ZnO) as an electron-selective contact. A detailed X-ray and ultraviolet photoelectron spectroscopy depth profile analysis is performed to reveal the mechanism of carrier selectivity and improved efficiency compared to homojunction cells grown under similar conditions. Moreover, a detailed loss analysis shows that the fabricated solar cell has the potential to reach more than 25% efficiency with further optimization. The device structure proposed in this paper will provide a route to reduce the complexity and cost of epitaxially grown cells while also allowing for the possibility to fabricate high-efficiency III–V solar cells using low-cost growth techniques (such as closed-space vapor transport and thin-film vapor–liquid–solid) where doping can be extremely challenging.