Ultrathin Zn₂SnO₄ (ZTO) passivated ZnO nanocone arrays for efficient and stable perovskite solar cells

ZnO has been widely applied as an efficient electron transport material (ETM) in perovskite solar cells (PSCs) due to advantages including easy fabrication and superior electron mobility. However, the thermal instability of perovskite layers deposited on top of ZnO has been a notorious issue, impeding the development of ZnO-based PSCs. Herein, we demonstrate a simple in-situ grown ZnO nanocone arrays and solution-processed ultrathin Zn₂SnO₄ (ZTO) passivation layer. The latter not only circumvented the thermal instability issue by physically isolating the perovskite film and ZnO, but assisted in charge extraction efficiency between the ETM/perovskite interface by passivating the defects on ZnO surface. Consequently, ZTO-passivated ZnO ETM based PSCs delivered a power conversion efficiency as high as 18.3% with a V_oc of 1.07 V, a J_sc of 23.2 mA/cm², a FF of 0.74 and remarkably enhanced stability. Therefore, introduction of utilizing a thin ZTO layer shows strong promise in ultimately solving the thermal instability issue of ZnO-based PSCs, paving the way for their practical use by making full use of the prominent advantages offered by ZnO.