Increasing the wettability and reducing excess PbI2 using diamine hydrobromides with different lengths at the buried interface of the 3D perovskite film

Abstract

In p–i–n type lead halide perovskite solar cells (PSCs), the poor wettability of the perovskite solution on the typically used hole transport layer, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), is detrimental to obtaining high quality perovskite films. Moreover, the formation of excess lead iodide (PbI₂) deteriorates the device stability. Herein, by introducing diamine hydrobromides with different lengths on the PTAA layer, its wettability is greatly increased, leading to a more uniform perovskite film and reduced trap density. Moreover, diamine hydrobromide can reduce excess PbI₂. Density functional theory (DFT) calculations further prove the strong interaction between diamine hydrobromides and PbI₂; diamine hydrobromides with different lengths present different binding energies with PbI₂. Among them, hexanediamine hydrobromate (HDADBr) has the lowest binding energy with PbI₂ and enables the least traps formed in the device. Moreover, HDADBr also has the weakest interaction with the I⁻-rich perovskite surface, and the distribution of the I density of states is expanded, which is more conducive to the diffusion of charge carriers. The best-performing PSC is achieved when HDADBr is used, which exhibits an improved power conversion efficiency (PCE) of 20.22% from 18.41% of the control device. The device stability is also notably improved; the PCE of the unencapsulated PSC remains at 90% of the initial value after 400 h of degradation.