Buried solvent assisted perovskite crystallization for efficient and stable inverted solar cells

Inverted (pin-type) organic-inorganic perovskite solar cells (PSCs) are very attractive for next generation photovoltaics, due to the advantages of low cost and facile fabrication. However, solution processed PSCs usually suffer from unsatisfactory power conversion efficiency (PCE), resulting from the defective perovskite layer and undesired interfacial property of perovskite (PVK)/PTAA. Here, pyridine (Py) is first used as a solvent for Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) for low temperature annealing process. Due to the enhancement of polaron delocalization of the PTAA chains affected by Py, PTAA film with low resistance is obtained. Meanwhile, buried Py induces the formation of high crystallinity perovskite film due to the presence of excess PbI2 coming from corrosion of cationic salts by pyridine and improved hydrophobic property of PTAA. Besides, PTAA (Py) based PVK film also exhibits lower defect densities and residual strain because lewis-based Py can bind to uncoordinated Pb2+ on perovskite surface. Finally, we achieve a champion PCE of 21.31% with PTAA (Py) based devices and the stability of unencapsulated devices is significantly improved.