Interface Engineering of CZTS/TiO2 Heterojunction Using Wide‐Bandgap Ga2O3 Passivation Interlayer for Efficient Charge Extraction

The greatest challenge for further improving the efficiency of Cu2ZnSnS4 (CZTS) solar cells is the high open‐circuit voltage (VOC) loss owing to nonradiation interface recombination. Controlling interfacial defect states and hence eliminating interface‐dominated recombination are imperative for device performance to achieve better charge extraction and collection. In this aspect, interface passivation is an effective way to resolve this issue. An ultrawide‐bandgap Ga2O3 film is inserted between CZTS absorber and TiO2 electron transport layer to passivate the electrically active interface trap states. The induced field‐effect passivation due to the existence of an additional field of Ga2O3 interlayer widens the depletion region width and cures the interfacial defect density. The significant photoluminescence quenching observed after inserting Ga2O3 at the CZTS/TiO2 heterojunction implies the effective injection of charge carriers from the CZTS absorber to TiO2 layer owing to reduced interface defect density. Meanwhile, the substantial decrement in dark current and response time of device with passivated interface further advocates the findings. Herein, a route to understand the variation in interfacial electrical properties after inserting a thin dielectric layer at the interface is provided, which can be beneficial for the further study of CZTS‐based optoelectronic device applications. To address the carrier recombination issue at the CZTS/TiO2 heterojunction, a thin Ga2O3 interfacial layer is deposited which passivates electrically active interface trap states. The additional built‐in electric field created by the high density of fixed charges in the Ga2O3 dielectric layer declines the probability of photoexcited electron–hole recombination at the interface and enhances charge transfer.