The effects of pyridine molecules structure on the defects passivation of perovskite solar cells

Pyridine molecules have been widely used to improve the performances of perovskite solar cells (PSCs). However, the effects of pyridine molecular structure, especially the functional group, on the defects passivation of perovskite solar cell have a lack of investigation. In this work, we introduced three pyridine molecules as additives into perovskite layer, including pyridine (PY), 4-methyl-pyridine (MP) and 4-tertbutyl pyridine (TBP), to investigate the influences of the molecular structure on the surface-defect passivation and long-term stability of perovskite solar cells. In fact, the pyridine molecules play two roles in the perovskite films. On the one hand, due to the different molecular structure, these pyridine molecules present differences in electron-pair-donor abilities (TBP > MP > PY), and then affect the interaction of pyridine molecule with Pb2+ in perovskite. Importantly, with the increase of interaction between different functional groups and Pb2+, the defect passivation effect was enhanced. What’s more, the crystal quality and light harvesting ability of the corresponding perovskite layer are improved by large crystal size and slow growth process. Consequently, PSCs with TBP, MP and PY respectively obtained a power conversion efficiency of 17.03%, 15.49% and 14.34%, which are higher than that of without additive (13.34%). On the other hand, owing to the hydrophobicity of groups, the pyridine molecules can enhance the moisture stability of devices. Significantly, the device based on the TBP-modified perovskite film exhibited improved moisture stability among the four type devices, owing to the best characteristic of the tertiary-butyl group with hydrophobicity in TBP.