In2O3-Ga2O3 Alloys as Potential Buffer Layers in CdTe Thin-Film Solar Cells

The efficiency of state-of-the-art CdTe solar cells remains limited by the relatively low open-circuit voltage (V-OC)(.) Improving the front interface is key towards realizing a higher V-OC after achieving the necessary bulk carrier density and lifetime. Recent efforts in identifying buffer layers beyond CdS have focused on MgxZn1-xO, which offers tunability of the band offsets, but often suffers from high interfacial defect densities. Ga2O3-based buffer layers demonstrate tremendous improvements in interfacial defect passivation in crystalline silicon and dye-sensitized solar cells, leading to record high V-OC, yet remain largely unexplored in CdTe-based devices. Here, we perform hybrid density-functional-theory calcula-tions to investigate pure Ga2O3 and InGaO3 alloys as a window layer in CdTe photovoltaics. We report calculated band offsets for several pairs of solid-solid interfaces comprising transparent conducting oxide (TCO) and CdTe heterojunctions. The results support a large conduction band offset spike of 0.67 eV for the CdTe/Ga2O3 (100) interface, while the offset is reduced to 0.18 eV for the InGaO3 alloy and matches closely with the preferred optimum value of 0.2 eV. Device-level modeling tests of CdTe solar cells integrating our results indicate that the highest efficiency is achieved with InGaO3 acting both as a buffer layer and TCO. Our results suggest that alloys of In2O3 and Ga2O3 may be attractive alternatives to MgxZn1-xO for tailoring optimal conduction-band offsets of the buffer and TCO layers in high-efficiency CdTe thin-film solar cells.

Automated summary

The research highlights the importance of improving the front interface to enhance open-circuit voltage (V-OC) in state-of-the-art CdTe solar cells. Ga2O3-based buffer layers show promising results in passivating interfacial defects, leading to high V-OC, and alloys of In2O3 and Ga2O3 may be attractive alternatives to MgxZn1-xO for optimizing conduction-band offsets in high-efficiency CdTe thin-film solar cells.