Enhancement of perovskite solar cell performance in ambient air through NH4Br incorporation: improved film quality and open-circuit voltage for nanorod-based devices

Abstract

Controlling the reaction rates between precursors and doping agents is an effective strategy for state-of-the-art perovskite solar cells (PSCs). In our research study, ammonium bromide (NH₄Br) was incorporated into a methylammonium iodide (MAI) precursor solution using a conventional two-step spin-coating technique, which resulted in a notable improvement in the performance of nanorod-based PSCs. Our findings indicate that adding NH₄Br results in a perovskite film free of PbI₂ residue, with an average grain size surpassing 1 μm. This effect is likely attributed to NH₄⁺, which regulates the reaction dynamics between MAI and PbI₂. Furthermore, during the crystallization process, Br⁻ partially replaces I⁻ in the MAPbI₃ lattice, causing lattice contraction that enhances the open-circuit voltage. Photovoltaic testing revealed that as the concentration of NH₄Br increased, the cell efficiency initially improved, reaching a peak before declining. Significantly, when the NH₄Br concentration reached 12 mg ml⁻¹, the device attained a maximum power conversion efficiency (PCE) of 19.07%, marking an impressive 26.8% enhancement compared to devices without NH₄Br.