Long-range exciton transport and slow annihilation in two-dimensional hybrid perovskites

Abstract

Two-dimensional hybrid organic-inorganic perovskites with strongly bound excitons and tunable structures are desirable for optoelectronic applications. Exciton transport and annihilation are two key processes in determining device efficiencies; however, a thorough understanding of these processes is hindered by that annihilation rates are often convoluted with exciton diffusion constants. Here we employ transient absorption microscopy to disentangle quantum-well-thickness-dependent exciton diffusion and annihilation in twodimensional perovskites, unraveling the key role of electron-hole interactions and dielectric screening. The exciton diffusion constant is found to increase with quantum-well thickness, ranging from 0.06 ± 0.03 to 0.34 ± 0.03 cm 2 s −1 , which leads to long-range exciton diffusion over hundreds of nanometers. The exciton annihilation rates are more than one order of magnitude lower than those found in the monolayers of transition metal dichalcogenides. The combination of long-range exciton transport and slow annihilation highlights the unique attributes of two-dimensional perovskites as an exciting class of optoelectronic materials.

Ultrafast Exciton Transport with a Long Diffusion Length in Layered Perovskites with Organic Cation Functionalization

“…The initial exciton population should follow the Gaussian distribution of the excitation beam. [24] At Figure 1. Transient photoluminescence mapping for in-plane exciton diffusion study.…”

“…[25][26][27][28] The corresponding in-plane exciton diffusion lengths were derived to be around 160 nm, which was much smaller than the film thickness (≈400-500 nm) to absorb most of sun light within absorption spectral range. [20,24] Soon Layered perovskites have been employed for various optoelectronic devices including solar cells and light-emitting diodes for improved stability, which need exciton transport along both the in-plane and the out-of-plane directions. However, it is not clear yet what determines the exciton transport along the in-plane direction, which is important to understand its impact toward electronic devices.…”

“…The excitation intensities were kept at 2.7 × 10 12 cm −2 , corresponding to an average bulk density of 5.2 × 10 16 cm −3 within the absorption length, below the estimated Mott density of 10 14 cm −2 and in the linear regime, to ensure PL signal proportional to the exciton density. [24,28,30] The diffusion mappings of BA-N1, BA-N2, and BA-N3 in Figure 2a-c show the broadening of PL distribution along the x-axis after excitation. For BA-N1 and BA-N2, the PL emission spots maintain a near constant size in the given time range, indicating a very limited number of excitons could diffuse out of the excitation spot.…”

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

“…The faster PL decay maybe not due to self‐annihilation of excitons, given the low annihilation rates found in RR‐2D perovskites. [ 37 ] In the adopted exciton configuration (front side), excitons should be primarily generated near the upper surface of perovskite films and the probed PL can either originate from the excitons generated directly in the 3D phase or those transferred from lower n ‐value species. To this end, the faster PL decay in the aqueous precursor processed perovskite could imply the promotion of exciton dissociation at the interface between different n ‐value species (acting as a p‐n junction), [ 35 ] which is in line with the enhanced EQE shown in Figure 1d.…”

Фотоэлектрические свойства композитных пленок на основе металлоорганического перовскита CH-=SUB=-3-=/SUB=-NH-=SUB=-3-=/SUB=-PbBr-=SUB=-3-=/SUB=- модифицированного смешанным эфиром целлюлозы

“…Это приводит к появлению свободных носителей заряда в образце под воздействием света. Из-за низкой подвижности экситонов в органических полупроводниках, длина их диффузии, как правило, ограничена ∼ 10 nm [27][28][29], однако известно, что в пленках металлоорганических перовскитов длина диффузии на порядок больше -до 100−120 nm в темноте и до 360 nm под воздействием света [30,31]. Вклад в фототок вносят только фотоны, поглощенные на характерной длине диффузии экситонов, что обеспечивает их транспорт к границе раздела и генерацию свободных носителей заряда.…”