Abstract
Effective passivation and stabilization of both the inside and interface of a perovskite layer are crucial for perovskite solar cells (PSCs), in terms of efficiency, reproducibility, and stability. Here, the first formamidinium lead iodide (delta-FAPbI(3)) polymorph passivated and stabilized MAPbI(3) PSCs are reported. This novel MAPbI(3)/delta-FAPbI(3) structure is realized via treating a mixed organic cation MA(x)FA(1-x)PbI(3) perovskite film with methylamine (MA) gas. In addition to the morphology healing, MA gas can also induce the formation of delta-FAPbI(3) phase within the perovskite film. The in situ formed 1D delta-FAPbI(3) polymorph behaves like an organic scaffold that can passivate the trap state, tunnel contact, and restrict organic-cation diffusion. As a result, the device efficiency is easily boosted to 21%. Furthermore, the stability of the MAPbI(3)/delta-FAPbI(3) film is also obviously improved. This delta-FAPbI(3) phase passivation strategy opens up a new direction of perovskite structure modification for further improving stability without sacrificing efficiency.