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Reduced energy loss enabled by thiophene-based interlayers for high performance and stable perovskite solar cells

Jiankai Zhang,Huangzhong Yu

The excessive energy loss (Eloss) mainly resulting from the energetic offsets between different layers and defect state-induced charge trapping and recombination limits the further development of perovskite solar cells (PVSCs). In this work, three solution-processed thiophene-based interlayers were firstly introduced to reduce the Eloss in PVSCs by optimizing the surface electronic states of the SnO2 electron transport layer (ETL) and improving the MAPbI3 film quality. The thiophene-based interlayers improve the conductivity and reduce the work function of SnO2 ETLs, resulting in more efficient electron transportation. Downward band-bending occurs at the SnO2/MAPbI3 interface owing to the permanent dipole moment of these interlayers, which enables more efficient charge carrier extraction and lower Eloss for PVSCs. In addition, the sulfur atoms of the thiophene rings with a lone pair of electrons can bond with the under-coordinated Pb2+ of MAPbI3, thus passivating the ion defect states and reducing the defect state-induced charge carrier trapping and recombination at the SnO2/MAPbI3 interface. These interlayers change the hydrophilicity of the SnO2 surface and promote the formation of high quality MAPbI3 films with larger grain size and fewer grain boundaries, improving the stability of PVSCs. Combining these desirable advantages, the optimized MAPbI3-based PVSCs achieve a highest power conversion efficiency (PCE) of 20.61% with a high open-circuit voltage (VOC) of 1.117 V and fill factor (FF) over 80%, which is higher than that of the pristine PVSCs with a highest PCE of 17.54%. The optimized PVSCs without any encapsulation show higher thermal and humidity stability compared with the pristine PVSCs. Therefore, this work demonstrates an effective way to reduce Eloss, as well as improving both the performance and stability of PVSCs by utilizing thiophene-based interlayers to modify the interface of SnO2/MAPbI3.