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

Abstract

The excessive energy loss (E_loss) 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 E_loss 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 E_loss 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 (V_OC) 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 E_loss, as well as improving both the performance and stability of PVSCs by utilizing thiophene-based interlayers to modify the interface of SnO₂/MAPbI₃.