Exciton Diffusion Lengths and Dissociation Rates in CsPbBr₃ Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures

Abstract

These properties have led to an enormous progress in various optoelectronic applications, especially to the impressive advances in the efficiency of photovoltaics that surged from 3.8% to 22% during the past few years. [5][6][7][8][9] Although most early research studies were focused on bulk thin film perovskites, very recently there has been a growing interest in exploring perovskite nanocrystals (NCs) for various applications due to their enhanced stability in the presence of ligands. [10][11][12][13] Several studies have already shown that perovskite NCs possess great potential for solution-processable photovoltaic devices under ambient atmosphere due to their high environmental and thermodynamic stabilities. [14][15][16] Other studies demonstrate the charge transfer dynamics for perovskite NCs in heterojunctions showing great potential for charge extraction in further applications. [17][18][19][20] Most reported perovskite photovoltaic devices are generally fabricated in a layer-by-layer configuration in which the exciton dissociation occurs at the interface of the perovskite NC layer and the respective electron or hole-transport layer. Therefore, the device performance relies on the diffusion of excitons or free carriers in the perovskite NC layer, which is reported as a fatal issue for ligand-capped colloidal NCs. [21][22][23][24] It is worth mentioning that organic semiconductor-based photovoltaic devices also suffer from similar problems. In order to enrich the donor-acceptor interfaces as well as to shrink the exciton diffusion path length, blend structures (donor and acceptor materials are mixed in one layer) have often been employed for achieving highly efficient organic photovoltaic devices. [25][26][27][28] However, it is difficult to fabricate such blend structures based on bulk thin film perovskites which are grown using precursors dissolved in polar solvents such as dimethylformamide and dimethyl sulfoxide. [5][6][7][8][9] In contrast, perovskite NCs fortunately are commonly dispersed in organic solvents in which organic electron-acceptor materials such as the fullerene derivative phenyl-C 61 -butyric acid methyl ester (PCBM) can be dissolved as well. This enables the fabrication of perovskite NC/PCBM blend structures similar to bulk heterojunction configurations in organic photovoltaic devices. Recently, Shen et al. have shown the fabrication of Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr 3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness ...

Highly Efficient Photoluminescence and Lasing from Hydroxide Coated Fully Inorganic Perovskite Micro/Nano‐Rods

“…On the other hand, the blue emission exhibits a very long diffusion length. As the diffusion length of the CsPbBr 3 nanocrystals were widely reported from 290 nm to 9.2 μm, [40,41] our values are quite valid. A time resolved PL (TRPL) comparison of the two peaks is shown (Figure 6b).…”

State of the Art and Prospects for Halide Perovskite Nanocrystals

“…The electron transfer from CsPbBr 3 to 2D NPls is found to be faster as compared to the QDs due to larger surface area and greater density of states in 2D materials. There are also a few studies on charge-transfer dynamics between photoexcited non-perovskite semiconductors and perovskite NCs. − Yao et al studied the charge transfer and exciton diffusion process in bilayer and blend structures of CsPbBr 3 /PCBM interfaces . By varying the thickness of the CsPbBr 3 NC film on top of the PCBM layer in the bilayer heterostructure, they determined an exciton diffusion length of 290 ± 28 nm for CsPbBr 3 assembly.…”

Molecular engineering for high-performance fullerene broadband photodetectors

“…The results of fullerene-based broadband photodetectors are compared in Table 2. Our device shows higher responsivity [55][56][57][58] and faster response time 24, 56 than most of fullerene heterojunction devices.…”