Grain Size and Interface Modification via Cesium Carbonate Post-Treatment for Efficient SnO₂-Based Planar Perovskite Solar Cells

Tin dioxide (SnO2) has emerged as an effective electron transport layer (ETL) in perovskite solar cells because of its good chemical stability, low annealing temperature, and relatively high electron mobility. However, the defect sites derived from the low-temperature solution process inevitably affect the device performance. Here, we report cesium carbonate (Cs2CO3) as a modifier to improve the electronic property of the SnO2 ETL and passivate the defects at the perovskite/SnO2 interface. It is found that Cs2CO3 modification could reduce the roughness and improve the surface wettability of the SnO2 film, resulting in much larger perovskite grains. In addition, the Cs2CO3 treatment leads to a lower film work function, which effectively accelerates the electron transfer and inhibits the carrier recombination. As a consequence, the low-temperature-processed Cs2CO3-treated SnO2 enables a significantly enhanced power conversion efficiency of 19.5% in comparison with 15.6% of the pristine device. Moreover, the hysteresis of the devices is obviously suppressed because of the optimization of both perovskites and perovskite/SnO2 interfaces.