Impact of n-Butylammonium Bromide on the Chemical and Electronic Structure of Double-Cation Perovskite Thin Films

2D/3D perovskite heterostructures have emerged as a promising material composition to reduce nonradiative recombination in perovskite-based LEDs and solar cells. Such heterostructures can be created by a surface treatment with large organic cations, for example, n-butylammonium bromide (BABr). To understand the impact of the BABr surface treatment on the double-cation (Cs(0.17)FA(0.83)Pb(I0.6Br0.4)(3)) (FA = formamidinium) perovskite thin film and further optimize the corresponding structures, an in-depth understanding of the chemical and electronic properties of the involved surfaces, interfaces, and bulk is required. Hence, we study the impact of the BABr treatment with a combination of surface-sensitive X-ray photoelectron spectroscopy and bulk-sensitive resonant inelastic soft X-ray scattering (RIXS). A quantitative analysis of the BABr-treated perovskite thin film shows a modified chemical perovskite surface environment of carbon, nitrogen, bromine, iodine, and lead, indicating that the treatment leads to a perovskite surface with a modified composition and bonding structure. With K-edge RIXS, the local environment at the nitrogen and carbon atoms is probed, allowing us to identify the presence of BABr in the perovskite bulk albeit with a modified bonding environment. This, in turn, identifies a hidden parameter for the optimization of the BABr treatment and overall performance of 2D/3D perovskite solar cell absorbers.

Automated summary

The impact of BABr surface treatment on double-cation perovskite thin film was studied, revealing modifications in the surface environment which can be crucial for optimizing the treatment and enhancing the performance of perovskite solar cells.