Extracting Decay-Rate Ratios From Photoluminescence Quantum Efficiency Measurements in Optoelectronic Semiconductors

Abstract

Recombination rates in optoelectronic semiconductors are typically recorded using timeintensive and expensive measurements. Here we present a method to extract decay rate ratios in a facile and rapid manner using only photoluminescence quantum efficiency measurements, which we demonstrate on halide perovskite thin film samples. We combine these ratios with time-resolved photoluminescence data to extract absolute recombination rates, with excellent agreement when our approach is benchmarked against the more time-and infrastructureintensive technique of transient absorption spectroscopy. This approach also enables direct quantification of the ratio between total second order and radiative second order recombination rates. We demonstrate that radiative recombination is only a fraction of total second order recombination in the range of halide perovskite samples relevant for photovoltaics. We showcase the implications of rapid extraction of decay rates by extracting decay rate ratios on a microscale and by calculating the expected maximum efficiency of a solar cell fabricated from the measured perovskite films. We show that reducing first order losses will significantly improve solar cell efficiency for our samples until time-resolved photoluminescence lifetimes are longer than ~ 1 µs (at low excitation pulse intensity), but at this point second order nonradiative recombination limits the efficiency of perovskite solar cells. This work represents a framework for rapidly screening optoelectronic semiconductors with techniques widely accessible to many research groups, identifies decay processes which would otherwise be missed, and directly relates the extracted values to predicted device performance metrics.

Shallow Defects and Ultralong Photoluminescence Decay Times up to 280 µs in Triple-Cation Perovskites

“…These shallow traps are less problematic for device performance than deeper traps with given SRH lifetimes tn and tp but are still dominating the steady state properties. Furthermore, the signatures of shallow traps in transient and steady state experiments are difficult to distinguish from radiative recombination, which may have contributed to the wide spread of reported values for the radiative recombination coefficient in leadhalide perovskites [31][32][33][34][35][36] as well as the frequent reports on non-radiative contributions to the quadratic recombination coefficient 9,12,34,35,37 . Furthermore, the work highlights that the abundantly used approximations of equation ( 1) have to be applied with caution and should not be considered as the default recombination model.…”

“…Identifying the properties of the defects dominating non-radiative recombination is important for a variety of reasons: Depending on the dominant defect species, material optimization would have to use different strategies to reduce recombination and material characterization would have to develop different approaches of quantifying recombination. For deep traps charge-carrier lifetimes determined from transient photoluminescence (PL) as well as PL quantum yields are both viable methods to quantify recombination and the information content of both quantities is basically identical 12 . In the presence of deep traps, transient PL measurements would lead to monoexponential decays at sufficiently low injection conditions from which charge-carrier lifetimes could be extracted.…”

Shallow defects and variable photoluminescence decay times up to 280 µs in triple-cation perovskites

“…Furthermore, n 1 and p are typically considered negligible relative to n and p, implying that detrapping is neglected, which is typically a good approximation for dominant defect species, different material optimization strategies and characterization approaches are needed. For deep traps, both transient photoluminescence (PL) and PL quantum yields are viable methods to quantify recombination, and the information content of both quantities is basically identical 12 . In the presence of deep traps, transient PL measurements lead to monoexponential decays at sufficiently low injection conditions, from which charge carrier lifetimes can be extracted.…”

Hydrogen Bond-Assisted Dual Passivation for Blue Perovskite Light-Emitting Diodes

“…, where G the generation rate, k 2,r is the rate of radiative bimolecular recombination, k 2,nrad is nonradiative second-order recombination, and k 3 is the rate of Auger recombination. 48 The fitting rates are listed in Table S1, and the k 2,r of the perovskite was improved with the DPPA passivation. Meanwhile, the time-resolved photoluminescence (TRPL) decay curves of pristine and DPPA-incorporated perovskite films at different excitation fluences are displayed in Figure 3c and Figure S4.…”

“…As shown in Figure b, the DPPA-passivated perovskite exhibits higher PLQY than pristine perovskite at different excitation fluence. According to the model: normald n normald t = G − k 2 , r n 2 − k 2 , normaln normalr normala normald n 2 − k 3 n 3 , where G is the generation rate, k 2,r is the rate of radiative bimolecular recombination, k 2,nrad is nonradiative second-order recombination, and k 3 is the rate of Auger recombination . The fitting rates are listed in Table S1, and the k 2,r of the perovskite was improved with the DPPA passivation.…”