Thermal Stability-Enhanced and High-Efficiency Planar Perovskite Solar Cells with Interface Passivation

As electron transport layer (ETL) of perovskite solar cells, oxide semiconductor Zinc oxide (ZnO) has been attracted great attention due to its relatively high mobility, optical transparency, low temperature fabrication and good environment stability. However, the nature of ZnO will react with the patron on methylamine, which would deteriorate the performances of cells. Although many methods including high temperature annealing, doping and surface modification have been studied to improve the efficiency and stability of perovskite solar cells with ZnO ETL, devices remains relatively low efficiency and stability. Herein, we adopted a novel multi-step annealing method to deposit a porous PbI2 film and improved the quality and uniformity of perovskite films. The cells with ZnO ETL were fabricated at the temperature of <150 degrees C by solution processing. The power conversion efficiency (PCE) of the device fabricated by the novel annealing method increased from 15.5% to 17.5%. In order to enhance the thermal stability of CH3NH3PbI3 (MAPbI(3)) on the ZnO surface, a thin layer of small molecule [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) was inserted between the ZnO layer and perovskite film. Interestingly, the PCE of PCBM-passivated cells could reach nearly 19.1%. To our best knowledge, this is the highest PCE value of ZnO-based perovskite solar cells until now. More importantly, PCBM modification could effectively suppress the decomposition of MAPbI(3) and improve the thermal stability of cells. Therefore, the ZnO is a promising candidate of electron transport material for perovskite solar cells in the future applications.