Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling

Summary The internal luminescence quantum efficiency ( Q i lum ) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine Q i lum from the experimentally accessible external luminescence quantum efficiency ( Q e lum ), 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 CH3NH3PbI3 films with exceptionally high Q e lum up to 47.4% corrects previous estimates for Q i lum of ∼90% to a real benchmark of 78.0% ± 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.