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

TL;DR

This paper introduces an accurate method to determine the internal luminescence quantum efficiency of perovskite films by accounting for photon recycling and escape probability, revealing higher efficiencies and potential for reducing non-radiative losses.

Contribution

The authors develop a curve fitting model to precisely quantify photon escape probability from PL spectra, enabling more accurate assessment of internal quantum efficiency in perovskite films.

Findings

Photon escape probability is over 10% higher than previous assumptions.

Achieved a record external luminescence quantum efficiency of 47.4%.

Internal quantum efficiency of 78.0% indicates more room for efficiency improvements.

Abstract

The internal luminescence quantum efficiency ($Q_\mathrm{i}^\mathrm{lum}$) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine $Q_\mathrm{i}^\mathrm{lum}$ of perovskite films from the experimentally accessible external luminescence quantum efficiency ($Q_\mathrm{e}^\mathrm{lum}$) it is essential to account for photon recycling, and this requires knowledge of the photon escape probability ($p_\mathrm{e}$). Here, we establish an analysis procedure based on a curve fitting model that accurately determines $p_\mathrm{e}$ 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 $p_\mathrm{e}$ being more than 10% higher in absolute terms compared to earlier assumptions. Applying our model to CH$_3$NH$_3$PbI$_3$ films with exceptionally high $Q_\mathrm{e}^\mathrm{lum}$ up to 47.4% sets a real benchmark for $Q_\mathrm{i}^\mathrm{lum}$ at $78.0 \pm 0.5\%$, revealing there is beyond a factor of two more scope for reducing non-radiative recombination than previously thought.