Carrier Trapping Deactivation by Halide Alloying in Formamidinium-Based Lead Iodide Perovskites

Formamidinium lead iodide (FAPbI3) is the benchmark material for the most efficient near-infrared perovskite light-emitting diodes (LEDs) and a promising gain medium for perovskite-based coherent light sources. Thus, it is crucial to understand and control its defect chemistry to harness the full potential of its exceptional radiative recombination properties. Here, this topic is addressed by tailoring the I- to Br- ratio in the perovskite composition. It is found that introducing small Br- quantities improves the yield of radiative recombination with a beneficial impact on both spontaneous and amplified spontaneous emission (ASE) and improves the semiconductor photostability leading to reduced luminescence efficiency roll-off and enhanced radiance in LEDs. By employing photoemission electron microscopy (PEEM), this improvement in optoelectronic performance can be directly correlated to a reduced hole-trapping activity achieved by replacing iodide with bromide, thus, providing a convenient yet powerful synthetic approach to control the defect chemistry of the material and fostering its implementation in advanced photonic platforms. Formamidinium lead iodide (FAPbI3) is the current benchmark perovskite composition for near-infrared emitters. Halide alloying with bromide in FAPbI3 reduces the activity of the detrimental interstitial iodide, obtaining perovskite compositions with improved optoelectronic properties, including improved photo-stability and reduced trapping of charge carriers. The reduced defect activity is directly probed using photo-emission electron microscopy (PEEM).image