This work investigates the effect of energetically shallow and deep surface defects in MAPbI3 films on the evolution of their photoluminescence properties upon exposure to ambient environment.
The internal luminescence quantum efficiency (Q lum i ) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine Q lum i from the experimentally accessible external luminescence quantum efficiency (Q lum e ), it is essential to account for photon recycling, and this requires knowledge of the photon escape probability (p e ). Here, we establish an analysis procedure based on a curve-fitting model that accurately determines p e of perovskite films from photoluminescence (PL) spectra measured with a confocal microscope and an integrating sphere setup. We show that scattering-induced outcoupling of initially trapped PL explains commonly observed red-shifted and broadened PL spectral shapes and leads to p e being more than a factor of two higher compared with earlier assumptions. Applying our model to CH 3 NH 3 PbI 3 films with exceptionally high Q lum e up to 47.4% corrects previous estimates for Q lum i of $90% to a real benchmark of 78.0% G 0.5%. Thereby, our study reveals there is beyond a factor of two more scope for reducing non-radiative recombination in perovskite films than previously thought.
The wide‐bandgap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light‐emitting diodes. Despite its utility, there is a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examined in detail. Although photovoltaic cells based on these solution changes exhibit similar initial performance, shelf storage depends strongly on precursor solution stoichiometry. While all devices exhibit some degree of healing, bromide‐deficient films show a remarkable improvement, more than doubling in their photoconversion efficiency. Photoluminescence spectroscopy experiments performed under different atmospheres suggest that this increase is due, in part, to a trap‐healing mechanism that occurs upon exposure to the environment. The results highlight the importance of understanding and manipulating defects in lead halide perovskites to produce long‐lasting, stable devices.
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