Abstract
Photovoltaic devices based on metal halide perovskites are rapidly improving in efficiency. Once the Shockley–Queisser limit is reached, charge-carrier extraction will be limited only by radiative bimolecular recombination of electrons with holes. Yet, this fundamental process, and its link with material stoichiometry, is still poorly understood. Here we show that bimolecular charge-carrier recombination in methylammonium lead triiodide perovskite can be fully explained as the inverse process of absorption. By correctly accounting for contributions to the absorption from excitons and electron-hole continuum states, we are able to utilise the van Roosbroeck–Shockley relation to determine bimolecular recombination rate constants from absorption spectra. We show that the sharpening of photon, electron and hole distribution functions significantly enhances bimolecular charge recombination as the temperature is lowered, mirroring trends in transient spectroscopy. Our findings provide vital understanding of band-to-band recombination processes in this hybrid perovskite, which comprise direct, fully radiative transitions between thermalized electrons and holes.
Highlights
Photovoltaic devices based on metal halide perovskites are rapidly improving in efficiency
Previous transient spectroscopic experiments have revealed the value of rate constants associated with different chargerecombination processes in hybrid perovskites, based on the measurements of transient absorption[9,10,11,12], photoluminescence[13,14,15] and terahertz photoconductivity[16,17] dynamics
Such separation is usually achieved through Elliott’s theory[37], previous attempts for metal halide perovskites have found significant deviations from experimental data for this theory at energies sufficiently above the band gap[12,38,39], which calls into question the rationale for using this model
Summary
Photovoltaic devices based on metal halide perovskites are rapidly improving in efficiency. Our evaluation of these factors suggest that within ~100 meV, the simplified assumptions of Elliott’s theory holds, allowing us to perform an analysis of band-edge charge-carrier recombination based on the continuum states extracted from this model.
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