Unveiling microscopic carrier loss mechanisms in 12% efficient Cu2ZnSnSe4 solar cells

Abstract Carrier loss mechanisms at microscopic regions is imperative for high-performance polycrystalline inorganic thin-film solar cells. Despite the progress on Kesterite, a promising environmental-benign and earth-abundant thin-film photovoltaic material, the microscopic carrier loss mechanisms and their impact on device performance remain unknown. Herein, we unveil these mechanisms in state-of-the-art Cu 2 ZnSnSe 4 (CZTSe) solar cells using a framework that links microscopic-structural and optoelectronic characterizations with three-dimensional device simulations. The results indicate the CZTSe films have an encouraging intragrain minority carrier lifetime of >10 ns, a marginal radiative recombination loss through sub-band recombination and electrostatic potential fluctuation, whilst a large effective grain boundary recombination velocity of around 10 4 cm s -1 and a low net carrier density of ~1×10 15 cm -3 . We identify that severe grain boundary recombination and low net carrier density are the current limiting factors of device performance. The established framework can greatly advance the research of kesterite and other emerging photovoltaic materials.