Improvement in Sb₂Se₃ Solar Cell Efficiency through Band Alignment Engineering at the Buffer/Absorber Interface

Abstract

Energy band alignment plays an important role in heterojunction thin-film solar cells. In this work, we report the application of ternary Cd _xZn_{1- x}S buffer layers in antimony selenide (Sb₂Se₃) thin-film solar cells. The results of our study revealed that the Cd/Zn element ratios not only affected the optical band gap of Cd _xZn_{1- x}S buffers but also modified the band alignment at the junction interface. A Sb₂Se₃ solar cell with an optimal conduction-band offset value (0.34 eV) exhibited an efficiency of 6.71%, which represents a relative 32.1% enhancement as compared to the reference CdS/Sb₂Se₃ solar cell. The results further indicated that a "spike"-like band structure suppressed the recombination rate at the interface and hence increased the device open-circuit voltage and fill factor. Electrochemical impedance spectroscopy analysis exhibited that the Cd _xZn_{1- x}S/Sb₂Se₃ solar cell had higher recombination resistance and longer carrier lifetime than the CdS/Sb₂Se₃ device.