Two‐Dimensional Halide Perovskites in Solar Cells: 2D or not 2D?

Ortiz‐Cervantes, Carmen; Carmona-Monroy, Paulina; Solis‐Ibarra, Diego

doi:10.1002/cssc.201802992

Cited by 214 publications

(245 citation statements)

References 119 publications

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“…To explore compositional variations, we substitute phenetylamonium (PEA) with butylammonium (BA) -another commonly used spacer molecule for two-dimensional perovskites. 20,28,29,32,43,[52][53][54] Figure 3a displays the MSD of the (BA)2PbI4 perovskite, again showing the distinct transition from normal diffusion to a subdiffusive regime. However, as compared to (PEA)2PbI4, excitons in (BA)2PbI4 are remarkably less mobile, displaying a diffusivity of only 0.013 ± 0.002 cm 2 /s, which is over an order of magnitude smaller than that of (PEA)2PbI4 with 0.192 ± 0.013 cm 2 /s (green curve shown in Figure 3a for comparison).…”

Section: Resultsmentioning

confidence: 99%

Exciton diffusion in two-dimensional metal-halide perovskites

et al. 2020

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Two-dimensional perovskites, in which inorganic layers are stabilized by organic spacer molecules, are attracting increasing attention as a more robust analogue to the conventional three-dimensional metal-halide perovskites. However, reducing the perovskite dimensionality alters their optoelectronic properties dramatically, yielding excited states that are dominated by bound electron-hole pairs known as excitons, rather than by free charge carriers common to their bulk counterparts. Despite the growing interest in two-dimensional perovskites for both light harvesting and light emitting applications, the full impact of the excitonic nature on their optoelectronic properties remains unclear, particularly regarding the spatial dynamics of the excitons within the two-dimensional (2D) plane.Here, we present direct measurements of in-plane exciton transport in single-crystalline layered perovskites. Using time-resolved fluorescence microscopy, we show that excitons undergo an initial fast, intrinsic normal diffusion through the crystalline plane, followed by a transition to a slower subdiffusive regime as excitons get trapped. Interestingly, the early intrinsic exciton diffusivity depends sensitively on the choice of organic spacer. We find a clear correlation between the stiffness of the lattice and the diffusivity, suggesting exciton-phonon interactions to be dominant in determining the spatial dynamics of the excitons in these materials. Our findings provide a clear design strategy to optimize exciton transport in these systems. lead, tin), X is a halide anion (chloride, bromide, iodide), L is a long organic spacer molecule, and n is the number of octahedra that make up the thickness of the inorganic layer. The separation into fewatom thick inorganic layers yields strong quantum and dielectric confinement effects. 38 As a result, the exciton binding energies in 2D perovskites can be as high as several hundreds of meVs, which is around an order of magnitude larger than those found in bulk perovskites. [39][40][41] The excitonic character of the excited state is accompanied by an effective widening of the bandgap, an increase in the oscillator strength, and a narrowing of the emission spectrum. [40][41][42] The strongest confinement effects are observed for n = 1, where the excited state is confined to a single B-X-octahedral layer (see Figure 1a).Light harvesting using 2D perovskites relies on the efficient transport of excitons and their subsequent separation into free charges. 43 This stands in contrast to bulk perovskites in which free charges are generated instantaneously thanks to the small exciton binding energy. 39 Particularly, with excitons being neutral quasi-particles, the charge extraction becomes significantly more challenging as they cannot be guided to the electrodes through an external electric field. 44 Excitons need to diffuse to an interface before the electron and hole can be efficiently separated into free charges. 45 On the other hand, for light emitting applications the spatial displacement is ...

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Section: Resultsmentioning

confidence: 99%

Exciton diffusion in two-dimensional metal-halide perovskites

et al. 2020

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“…[ 7 ] Unfavorably, quasi‐2D perovskites are generally associated with a large exciton binding energy (hundreds of meV) due to the insulating nature of bulky organic ligands and the specific layered arrangement. [ 11,12 ] As a result, charge transport and extraction are hindered in quasi‐2D PSCs. To date, the highest reported PCEs of quasi‐2D PSCs ( n ≤ 5) remain around 18%, [ 13–15 ] showing considerable performance gaps with regard to 3D‐PSCs.…”

Section: Figurementioning

confidence: 99%

Water‐Assisted Crystal Growth in Quasi‐2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

Wang

et al. 2020

Advanced Energy Materials

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Perovskite solar cells (PSCs) employing 3D organic-inorganic hybrid perovskite photoabsorbers have received tremendous progress with state-of-the-art power conversion efficiency (PCE) exceeding 25% during the last a dozen years. [1] However, ambient instability of 3D perovskite materials remains a critical obstacle for realistic applications of PSCs. [2,3] A strategy in addressing the poor stability is to reduce the structural dimensionality of perovskites via the introduction of long-chain organic ligands by forming Ruddlesden-Popper (RP) quasi-2D perovskites. [4,5] The organic ligands are bound to the 3D inorganic framework via coulombic interactions, resulting in a layered structure. The general formula of RP-2D perovskites takes the form of (L) 2 A n−1 Pb n I 3n+1 (n = 1, 2, 3, 4…) where A is the methylammonium (MA +), formamidinium (FA +), or cesium (Cs +) cations, L is the bulky organic ligands, e.g., butylammonium (BA +) or 2-phenylethylammonium (PEA +), and n is the number of layers in the [PbI 6 ] 4− octahedral sheets. [4-7] The incorporation of hydrophobic bulky organic ligands can not only enhance the stability of perovskites with minimized permeation of water molecules but also increase the formation energy of perovskites to mitigate thermal degradation and ion migration. [8-10] These merits alongside the quantum confinement have rendered quasi-2D perovskites great potentials for optoelectronic applications with a wide tunability on the bandgap or photophysical properties. [7] Unfavorably, quasi-2D perovskites are generally associated with a large exciton binding energy (hundreds of meV) due to the insulating nature of bulky organic ligands and the specific layered arrangement. [11,12] As a result, charge transport and extraction are hindered in quasi-2D PSCs. To date, the highest reported PCEs of quasi-2D PSCs (n ≤ 5) remain around 18%, [13-15] showing considerable performance gaps with regard to 3D-PSCs. The PCE (η) of photovoltaic cells is determined by the general relation, J V P FF sc oc light η = × × (V oc is the open-circuit voltage, FF is the fill factor, and P light is the illumination intensity). In quasi-2D PSCs, the relatively low J sc is more restrictive for Organic-inorganic hybrid quasi-2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi-2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water-controlled crystal growth of quasi-2D perovskites are presented to achieve high-efficiency solar cells. It is demonstrated that the (BA) 2 MA 4 Pb 5 I 16-based PSCs (n = 5) processed with water-containing precursors display an increased short-circuit current density (J sc) of 19.01 mA cm −2 and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI•H 2 O), leading to modulations on the crystal orientation and phase distribution of various n-value components, which facilitate interphase charge tr...

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“…As a consequence, their chemical formulae were systematically changed according to the number of layers and crystal orientation plane. In specific, the chemical formula of (100), (110), and (111) oriented HP family are A′ 2 A n −1 B n X 3 n +1 , A′ 2 A m B m X 3 m +2 , and A′ 2 A q −1 B q X 3 q +3 , accordingly …”

Section: Structures and Propertiesmentioning

confidence: 99%

2D and Quasi‐2D Halide Perovskites: Applications and Progress

Kim

Huynh

Kim

et al. 2019

Physica Rapid Research Ltrs

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Two-dimensional (2D) and quasi-2D (q-2D) halide perovskites (HPs) offer a number of advantages compared with their three-dimensional (3D) counterparts for electronic and optoelectronic applications due to their tunable properties and superior stability. This mini-Review, at first is focused on the atomic structure and the optical and electrical properties of 2D and q-2D HPs. The unique properties of 2D HPs are addressed in comparison with 3D HPs. Recent progress in applications using 2D and q-2D HPs is summarized, such as in solar cells, lightemitting diodes, photodetectors, resistive random access memories, and artificial synapses. The main parameters that regulate the device performance and strategies for improving materials properties and device performance for each application are addressed. Finally, the perspective for the future development of 2D and q-2D HPs is discussed.

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Two‐Dimensional Halide Perovskites in Solar Cells: 2D or not 2D?

Cited by 214 publications

References 119 publications

Exciton diffusion in two-dimensional metal-halide perovskites

Exciton diffusion in two-dimensional metal-halide perovskites

Water‐Assisted Crystal Growth in Quasi‐2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

2D and Quasi‐2D Halide Perovskites: Applications and Progress

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