Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films

Ciesielski, Richard; Schäfer, Frank; Hartmann, Nicolai F.; Giesbrecht, Nadja; Bein, Thomas; Docampo, Pablo; Hartschuh, Achim

doi:10.1021/acsami.7b17938

Cited by 41 publications

(90 citation statements)

References 47 publications

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“…The carrier diffusion length of perovskites was reported ranging from 100 nm to more than 100 µm based on various methods . PL quenching (PLQ) is a commonly used method to determine the diffusion length and carrier lifetime for the perovskites, by simply fabricating the perovskite thin films in the presence or absence of a carrier‐quenching layer and modeling the PL decay to the diffusion model ( Figure a).…”

Section: Photogenerated Free Charge Carrier: Transport Recombinationmentioning

confidence: 99%

“…A number of studies have demonstrated that the carrier diffusion lengths measured from polycrystalline thin films are significantly shorter than those of single crystals (less than a few µm vs more than 100 µm), due to the existed grain boundaries in polycrystalline perovskites . Ensemble measurements for the determination of diffusion length are unable to monitor the impact of grain boundaries or local morphologies on the carrier transport.…”

Section: Photogenerated Free Charge Carrier: Transport Recombinationmentioning

confidence: 99%

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Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

2019

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their great success in photovoltaics (PVs), with a phenomenally rapid rise of the power conversion efficiency (PCE) from 3.8% [1] to over 23% [2,3] in the past few years. Such high PCE of perovskite solar cells has been ascribed to the ultralong carrier lifetimes, [4][5][6][7][8] long carrier diffusion lengths, [9][10][11][12][13][14] and the extraordinarily defect tolerance. [15][16][17] Following the success of perovskites in photovoltaics, research on light-emitting diodes (LEDs), [18,19] amplified spontaneous emission (ASE) or lasers, [20][21][22][23][24] and photodetectors [25][26][27][28][29] have also gained substantial interests. Meanwhile, the rapid progress of MHPs on various applications spurred a flurry of photophysical studies in order to understand the origin of the high performance of these devices, of which the nature of the photoexcitation species has been mostly debated. [5,22,30,31] Since the photoexcitation states near the bandgap affect the key processes such as charge transport and light emission of optoelectronic devices, there is no doubt that the investigation of electronic excitations near the optical band edge is crucial for MHPs. Such knowledge is essential not only for understanding the correlation between the fundamental photophysics and device performances, but also offering a guideline for their further applications with improved performances. Generally, there are two kinds of photoexcitations near the band edge for direct bandgap semiconductors: free carriers and excitons. Exciton binding energy that reflects the Coulomb interaction strength between photoexcited electrons and holes determines the balance of the populations between the two species. Typically, inorganic semiconductors are free-carrier materials with the exciton binding energies only in few meV at room temperature and their excited states being populated principally by free carriers. While organic semiconductors are excitonic materials with the exciton binding energies in hundreds of meV and thus excitons prevailing in the excited states. Whereas, MHPs that combine some merits of organic and inorganic semiconductors seem to stand for an exotic class of semiconductors between these two limiting cases, with the experimentally determined exciton binding energy varying in a wide range of 2 to more than 50 meV for the prototype perovskite MAPbI 3 . [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Such large variations of the exciton binding energies reported for MHPs give rise to a strongly debated question, that is, whether free carriers or excitons are generated upon photoexcitation? In other words, what is the nature of the photoexcitation species Metal halide perovskites (MHPs) have recently attracted great attention from the scientific community due to their excellent photovoltaic performance as well as their tremendous potential for other optoelectronic applications such as light-emitting diodes, lasers, and photodetectors. Despite the rapid progress in device applications, a solid unders...

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Section: Photogenerated Free Charge Carrier: Transport Recombinationmentioning

confidence: 99%

Section: Photogenerated Free Charge Carrier: Transport Recombinationmentioning

confidence: 99%

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

2019

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“…3b). As recent investigations have shown, the boundaries between the grains inside the layer do not cause quenching of the PL [21][22][23][24] and, It should be noted that, generally speaking, the diffusion equation is applicable only for homogeneous materials. It is obvious that polycrystalline perovskite layers are not homogeneous, since they contain not only bulk material, which in the first approximation can be considered the same in different grains, but also grain boundaries.…”

Section: Pl Decay Kinetics In Thin Perovskite Layersmentioning

confidence: 99%

Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films

Chirvony

Sekerbayev

Adl

et al. 2020

Journal of Luminescence

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One of distinguishing features of metal halide perovskites is their long (up to microseconds) photoluminescence (PL) lifetimes, which are regularly observed for this class of semiconductors in spite of their direct gap origin. It is difficult to explain this contradiction in the framework of usual two-level Jablonski photophysical diagram because the absorption coefficient (i.e., the oscillator strength of the direct optical transition) is too high in perovskites to hold such long PL lifetimes. In this paper, we describe practical steps how the PL decay kinetics of perovskites in the forms of (1) passivated nanocrystals and (2) thin multicrystalline films can be described. In case of nanocrystals, the three-level delayed luminescence model is described by including shallow non-quenching traps providing multiple trapping and de-trapping of carriers and thus essentially lengthening the observed PL lifetime. In the case of perovskite thin films limited by interfacial recombination, the PL decay kinetics is usually determined by the non-radiative recombination on the film surfaces and can be satisfactorily described in terms of one-dimensional diffusion equation. The limits of applicability of such approaches are discussed.

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“…On the other hand, optoelectronic properties are more difficult to probe within the bulk of these crystals, particularly on the microscale, due to the large optical absorption coefficients of these materials [22] . Time-resolved PL (TRPL) microscopy measurements allow us to study diffusive effects on the micro-scale [9,29,30] . Most TRPL studies on halide perovskites…”

mentioning

confidence: 99%

Visualizing Buried Local Carrier Diffusion in Halide Perovskite Crystals via Two-Photon Microscopy

et al. 2019

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Halide perovskites have shown great potential for light emission and photovoltaic applications due to their remarkable electronic properties and compatibility with cost-effective fabrication techniques. Although the device performances are promising, they are still limited by microscale heterogeneities in their photophysical properties. In particular, the relation between local heterogeneities and the diffusion of charge carriers at the surface and in the bulk, crucial for efficient collection of charges in a light harvesting device, is not well understood.Here, a photoluminescence tomography technique is developed in a confocal microscope using one-and two-photon excitation to distinguish between local surface and bulk diffusion of charge carriers in methylammonium lead bromide single crystals. The local temporal diffusion is probed at various excitation depths to build statistics of local electronic diffusion coefficients.The measured values range between 0.3 to 2 cm 2 .s -1 depending on the local trap density and the morphological environmenta distribution that would be missed from analogous macroscopic or surface-measurements. Tomographic images of carrier diffusion were reconstructed to reveal buried crystal defects that act as barriers to carrier transport. This work reveals a new framework to understand and homogenise diffusion pathways, which are extremely sensitive to local properties and buried defects.Over the past ten years, halide perovskites have emerged as strong candidates for various light-harvesting and light-emission applications [1][2][3] . The performances of perovskitebased photovoltaics (PV) and light-emitting diodes (LEDs) are now competing with mature, commercial technologies [4] . This rapid development has been made possible by the design of new halide perovskite compositions [5][6][7] which generally share properties of remarkably long carrier diffusion lengths (0.1-1 μm) [8,9] even when simple cost-effective fabrication techniques are employed. However, for halide perovskites to reach their full potential, one has to understand the microscopic heterogeneities that still limit their performances [10,11] . For instance, local defects, both at the surface and inside the bulk, trap charge carriers thus limiting their ability to diffuse through the material. It is therefore critical to investigate the diffusion mechanisms at the local scale to identify these trap sites and elucidate ways to mitigate their influence on carrier diffusion and recombination.Methylammonium lead bromide (MAPbBr3, MA=CH3NH3 + ) single crystals have remarkable photophysical properties as highlighted in recent reports on amplified spontaneous emission [12] and lasing phenomena [13,14] , two-photon absorption [15,16] , extreme sensitivity to environment [17] , excitonic properties [18,19] , and long carrier diffusion lengths [20] . Additionally, their optical properties are well-documented including their refractive index [21,22] and exciton binding energy [23] , and photon reabsorption has been quantified [22,24,25...

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Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films

Cited by 41 publications

References 47 publications

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films

Visualizing Buried Local Carrier Diffusion in Halide Perovskite Crystals via Two-Photon Microscopy

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