Regulation on electron density distribution of organic molecule passivator enables efficient and stable perovskite solar cells

Interfacial trap-mediated nonradiative charge recombination is a dominated limit to improving the efficiency and stability of perovskite solar cells (PSCs). The ionic nature of perovskite crystal enables molecular passivation methods through interaction between functional groups and unsaturated sites. However, a lack of in-depth understanding of the passivation mechanism and function of every functional group is a great challenge for the development of versatile passivators and further improvement of the PSCs performance. Herein, three 2-mercaptobenzothiazole (MBT) ligands featuring different functional groups which directly linking to their conjugated structure are employed to passivate interfacial defects and regulate crystallization. It is found that the increased electron density on conjugated ring structure and coordination sites gives a positive effect on the defect passivation and crystal growth. The MBT organic molecule with electron-donating group OCH3 gives the best passivation effects, while the molecule with electron-withdrawing group NO2 presents negative impacts. Furthermore, it is also demonstrated that the MBT based ligands containing multi-coordination sites (N, S and O atoms) present a strong coordination capacity with uncoordinated Pb2+ ion at the surface or grain boundaries of perovskite films. As a result, the MBT-OCH3 device shows a strikingly improved efficiency of 21.04 % along with excellent long-term stability. Therefore, this work opens a new line through the strategies to improve photovoltaic performance by modulating the electronic configuration of the passivation molecules.