Smoothed grain boundary grooves, passivated defects and released compressive stresses via bulk molecule doping for efficient perovskite solar cells

In preparing efficient and stable perovskite solar cells (PSCs), it is challenging to simultaneously overcome the inherent problems of grain boundary grooves (GBGs), residual stress, defect states in perovskite film. Herein, a small organic molecule additive, pyridinium 1,4-zwitterionic thiolates (PZT), is synthesized to prepare high-quality PZT-doped perovskite active layer through bulk molecule doping method. The PZT promotes the crystallization of perovskite, optimizes the crystal orientation, and smooths the GBGs of perovskite films. Meanwhile, PZT releases compressive stress and passivates the perovskite defects at the surface/interface as well as internal grain boundaries in the perovskite film, which inhibits the charge recombination and promotes the charge separation and transport efficiency in the bulk perovskite films through the atomic interaction at the perovskite/PZT interface. In addition, the PZT also inhibits ion migration in perovskite film and increases film hydrophobicity. Benefiting from the above benefits, the PSCs based on perovskite:PZT layer achieved a maximum power conversion efficiency of 23.45%, much higher than that (21.79%) of control device. They also show significantly improved long-term stability under different aging test conditions. Our work provides a guide for improving the performance of PSCs by designing suitable multifunctional molecules.