Abstract

When discussing semiconductor properties, we typically focus on carrier and defect concentrations, assuming these are sufficient to explain and predict electronic properties. In this talk, I present mapping of the photoluminescence quantum yield (PLQY) over repetition rate and pulse fluence (so-called “horse plots”),[1] together with multi-pulse time-resolved photoluminescence,[2] as experimental tools that, in principle, enable the extraction of physically meaningful models of charge-carrier dynamics in metal-halide perovskite semiconductors. However, their direct interpretation usually neglects the polycrystalline and nanostructured nature of perovskite films.

I argue that treating halide perovskite materials as homogeneous in space and time (the standard assumption in semiconductor theory) is frequently inadequate. At the nanoscale, charge dynamics can be governed by only a few carriers and defect states per grain, leading to “digitised” regimes requiring stochastic descriptions.[3] This manifests, for example, as photoluminescence blinking caused by individual metastable non-radiative centres.[4] Moreover, the grainy nature of the material, combined with the discrete nature of photon absorption, results in photoluminescence dynamics that differ markedly from bulk expectations, even at identical average defect concentrations. One important consequence of these effects is an increase in PLQY with decreasing crystal size below a certain threshold. This size dependence is unrelated to quantum confinement and instead originates from the discrete nature of light and defects. Thus, crystal size well beyond the quantum confinement regime plays a important role in determining PLQY , highlighting the importance of spatial structure on length scales of approximately 50–200 nm in luminescent materials and likely in solar cells.

[1] A. Kiligaridis, P.A. Frantsuzov, A. Yangui, S. Seth, J. Li, Q. An, Y. Vaynzof, I.G. Scheblykin, Are Shockley-Read-Hall and ABC models valid for lead halide perovskites?, Nat. Commun. 12 (2021) 3329. https://doi.org/10.1038/s41467-021-23275-w.

[2] A. Marunchenko, J. Kumar, D. Tatarinov, A.P. Pushkarev, Y. Vaynzof, I.G. Scheblykin, Hidden Photoexcitations Probed by Multipulse Photoluminescence, ACS Energy Lett. 9 (2024) 5898–5906. https://doi.org/10.1021/acsenergylett.4c02404.

[3] I.G. Scheblykin, Small Number of Defects per Nanostructure Leads to “Digital” Quenching of Photoluminescence: The Case of Metal Halide Perovskites, Adv. Energy Mater. 10 (2020) 2001724. https://doi.org/10.1002/aenm.202001724.

[4] A. Merdasa, Y. Tian, R. Camacho, A. Dobrovolsky, E. Debroye, E.L. Unger, J. Hofkens, V. Sundström, I.G. Scheblykin, “Supertrap” at Work: Extremely Efficient Nonradiative Recombination Channels in MAPbI 3 Perovskites Revealed by Luminescence Super-Resolution Imaging and Spectroscopy, ACS Nano 11 (2017) 5391–5404. https://doi.org/10.1021/acsnano.6b07407.