Direct measurement of radiative decay rates in metal halide perovskites

Simbula, Angelica; Pau, Riccardo; Liu, Fang; Wu, Luyan; Lai, Stefano; Lehmann, Alessandra Geddo; Filippetti, Alessio; Loi, Maria Antonietta; Marongiu, Daniela; Quochi, Francesco; Saba, Michele; Mura, Andrea; Bongiovanni, Giovanni

doi:10.1039/d1ee03426j

Cited by 10 publications

(8 citation statements)

References 57 publications

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“…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.…”

Section: Discussionmentioning

confidence: 99%

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

Yuan

Yan

Dreeßen

et al. 2023

Preprint

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Quantifying recombination in halide perovskites is a crucial prerequisite to control and improve the performance of perovskite-based solar cells. While both steady state and transient photoluminescence are frequently used to assess recombination in perovskite absorbers, quantitative analyses within a consistent model are seldomly reported. We use transient PL measurements with a large dynamic range of more than 10 orders of magnitude on triple-cation perovskite films showing long-lived photoluminescence transients featuring continuously changing decay times that range from tens of ns to hundreds of µs. We quantitatively explain both the transient and steady state PL with the presence of a high density of shallow defects and consequent significant rates of charge carrier trapping thereby showing that deep defects do not affect the recombination dynamics at all. The complex carrier kinetics caused by emission and recombination processes via shallow defects implies that reporting of only single lifetime values, as routinely done in literature, is meaningless for such materials. We show that the features indicative for shallow defects seen in the bare films remain dominant in finished devices and are therefore also crucial to understand the performance of perovskite solar cells.

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Section: Discussionmentioning

confidence: 99%

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

Yuan

Yan

Dreeßen

et al. 2023

Preprint

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“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27] Several experiments have started to explain such apparent contradiction by presenting evidences for the presence of free carriers among the optical excitations in layered perovskites. [28][29][30][31][32][33][34][35][36] Bimolecular recombination has been observed, with rates quadratic in the concentration of optical excitations, the hallmark of unbound carriers. The rst physical mechanism invoked to explain the abundance of free carriers has been exciton splitting by intragap edge states at crystalline grain boundaries.…”

Section: Introductionmentioning

confidence: 99%

Exciton splitting in 2D layered metal-halide perovskites

Simbula

Pitzalis

et al. 2023

Preprint

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Layered 2D perovskites are making inroads as materials for photovoltaics and light emitting diodes, but the photophysics of their optical excitations is still debated. Although their large exciton binding energies should hinder charge separation, significant evidence has been uncovered for an abundance of free carriers. Several explanations have been proposed, like exciton splitting at grain boundaries or polaron formation, without clarifying yet if excitons form and then split, or if the formation is prevented by competing relaxation processes. Here we address exciton stability in layered PEA2PbI4 in n = 1 Ruddlesden-Popper phase, both in form of thin film and single crystal. Samples are resonantly excited to directly inject cold excitons, whose dissociation is then demonstrated with femtosecond differential transmission. The results presented here establish the intrinsic nature of exciton dissociation in 2D Ruddlesden-Popper layered perovskites, demonstrating that they are free carrier semiconductors like their 3D counterparts, belonging to a universal photophysical framework.

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“…To qualitatively discuss these data, the ABC model for recombination dynamics and PLQY given in eqs and is used. d n d t = G ( t ) − k 1 n − ( k 2 r + k 2 nonr ) n 2 − k 3 n 3 PLQY ( n ) = k 2 normalr n k 1 + ( k 2 r + k 2 nonr ) n + k 3 n 2 where G ( t ) is the generation rate, k 1 is the trap-assisted recombination coefficient, k 2r and k 2nonr are radiative and nonradiative second-order rate coefficients, and k 3 is the Auger rate coefficient. The origin of k 2nonr is not entirely clear but could be related to a nonradiative process involving two free carriers and a trapped one. − As discussed below, inclusion of a k 2nonr is necessary to understand the observed changes in PLQY with bias. As seen from eq , the PLQY will first increase with carrier density until k 1 is negligible compared to ( k 2 + k 2nonr ) n .…”

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confidence: 99%

Enhancement of Amplified Spontaneous Emission by Electric Field in CsPbBr₃ Perovskites

Yang

Farag

et al. 2023

Nano Lett.

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Perovskite gain materials can sustain continuous-wave lasing at room-temperature. A first step toward the unachieved goal of electrically excited lasing would be an improvement in gain when electrical stimulation is added to the optical. However, to date, electrical stimulation supplementing optical has reduced gain performance. We find that amplified spontaneous emission (ASE) in a CsPbBr3 perovskite light-emitting diode (LED) held under invariant subthreshold optical excitation can be turned on/off by the addition/removal of an electric field. A positive bias voltage leads to a factor of 3 reduction in the optical ASE threshold, the cause of which can be attributed to an enhancement of the radiative rate. The slow components (10 s time scale) of the modulation in the photoluminescence and ASE when the voltage is changed suggest that the relocation of mobile ions trigger the increased radiative rate and observed lowering of ASE thresholds.

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Direct measurement of radiative decay rates in metal halide perovskites

Abstract: The rate of light emission per unit carrier concentration, or radiative rate, is a fundamental semiconductor parameter that determines the limit photoconversion efficiency of solar cells. In hybrid perovskites, a...

Cited by 10 publications

References 57 publications

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

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

Exciton splitting in 2D layered metal-halide perovskites

Enhancement of Amplified Spontaneous Emission by Electric Field in CsPbBr₃ Perovskites

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Direct measurement of radiative decay rates in metal halide perovskites

Abstract: The rate of light emission per unit carrier concentration, or radiative rate, is a fundamental semiconductor parameter that determines the limit photoconversion efficiency of solar cells. In hybrid perovskites, a...

Cited by 10 publications

References 57 publications

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

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

Exciton splitting in 2D layered metal-halide perovskites

Enhancement of Amplified Spontaneous Emission by Electric Field in CsPbBr3 Perovskites

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Enhancement of Amplified Spontaneous Emission by Electric Field in CsPbBr₃ Perovskites