Ammonium formate-engineered MA-free perovskite inks for solar cells and optoelectronic devices

Abstract

Perovskite solar cells (PSCs) are widely considered for scale-up and commercialization, while there are still challenges in the stability of devices and inks. The stability of devices is directly associated with the stability of the perovskite ink and is linked with formulations that inhibit degradation reactions. In this work, we demonstrate how ammonium formate (AF) fulfills this objective and results in more stable devices and inks. We start with a conventional triple-cation perovskite ink and observe that elimination of methylamine (MA) from the formulation, and especially adding AF to the formulation, leads to remarkably durable inks. Optimized perovskite films containing AF exhibit a compact/low-pinhole morphology, with enhanced photoluminescence (PL) intensity and almost no degradation at 85 °C for 56 days, in contrast to AF-free films. Carbon-based perovskite cells with AF-doped perovskite films demonstrate improved efficiency (up to 19.40%) and perform considerably better in steady-state power output (SPO) tests and ISOS-D1 stability assessments. These come with high electroluminescence (EL) of the PSC devices and lower charge transfer resistance due to the AF additive. Optimized AF-perovskite films are also evaluated as self-powered photodetectors, in combination with triboelectric nano-generators (TENGs), where they show improved detectivity compared to battery-powered photodetectors.