Quasi-Fermi level splitting, stability, and healing of high bandgap hybrid perovskites using photoluminescence, composition spread libraries, and post-synthesis treatments

Abstract

We show the optoelectronic quality and the stability of thousands of compositions of hybrid perovskites (including the range of halide substitutions) and methods to re-grow hybrid perovskites to improve their optoelectronic quality. Hyperspectral maps of steady-state absolute intensity photoluminescence (AIPL) are used to determine the quasi-Fermi level splitting (QFLS) for the combinatorial libraries. For methyl ammonium iodobromides, the QFLS upon first illumination increases with bandgap and reaches a maximum of 1.27 eV under 1 Sun illumination intensity for a bandgap of 1.75 eV However, the optoelectronic quality, defined as the ratio of the QFLS to the maximum theoretical QFLS for bandgap, decreases with bandgap from around 88% for 1.60 eV bandgap down to 82% for 1.84 eV bandgap. We show the effects of water exposure, air exposure and the effects of re-growing the films under several conditions.