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Exciton Diffusion Lengths and Dissociation Rates in CsPbBr 3 Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures
Author(s) -
Yao EnPing,
Bohn Bernhard J.,
Tong Yu,
Huang He,
Polavarapu Lakshminarayana,
Feldmann Jochen
Publication year - 2019
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201801776
Subject(s) - materials science , photoactive layer , exciton , fullerene , femtosecond , heterojunction , nanocrystal , perovskite (structure) , optoelectronics , chemical physics , solar cell , chemical engineering , nanotechnology , polymer solar cell , optics , organic chemistry , laser , chemistry , physics , engineering , quantum mechanics
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 of the NC layer on top of the PCBM in the layer‐by‐layer heterostructure, an exciton diffusion length of 290 ± 28 nm for CsPbBr 3 NC is extracted. The diffusion process is followed by an ultrafast exciton dissociation (within 200 fs) at the CsPbBr 3 NC/PCBM interface. In blend structures an overall faster charge transfer process is observed. Furthermore, photoconductivity measurements on a blend structure‐based photodetector reveal an effective charge extraction from the active layer resulting in a high photosensitivity. DT measurements on this blend structure including adjacent electron‐ or hole‐transport layers give insight into the extraction process and suggest a certain degree of phase segregation, which assists the charge collection.