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

• Published in: Advanced materials (Weinheim) Vol. 32; no. 46; pp. e2004080 - n/a
• Main Authors: Xiao, Xun, Wu, Marvin, Ni, Zhenyi, Xu, Shuang, Chen, Shangshang, Hu, Jun, Rudd, Peter Neil, You, Wei, Huang, Jinsong
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2020; Wiley Blackwell (John Wiley & Sons)
• Subjects: Cations; Density functional theory; Diffusion layers; Diffusion length; Distortion; Electronic devices; exciton transport; Excitons; Fluorine; layered perovskites; Luminous intensity; Materials science; Optoelectronic devices; organic cations; Perovskites; Photoluminescence; Photovoltaic cells; Solar cells; Temperature dependence; transient photoluminescence mapping
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202004080

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. Here, by employing both steady‐state and transient photoluminescence mapping, it is found that in‐plane exciton diffusivities in layered perovskites are sensitive to both the number of layers and organic cations. Apart from exciton–phonon coupling, the octahedral distortion is revealed to significantly affect the exciton diffusion process, determined by temperature‐dependent photoluminescence, light‐intensity‐dependent time‐resolved photoluminescence, and density function theory calculations. A simple fluorine substitution to phenethylammonium for the organic cations to tune the structural rigidity and octahedral distortion yields a record exciton diffusivity of 1.91 cm2 s−1 and a diffusion length of 405 nm along the in‐plane direction. This study provides guidance to manipulate exciton diffusion by modifying organic cations in layered perovskites. Apart from exciton–phonon coupling, octahedral distortion is revealed to significantly affect the exciton diffusion process. A simple fluorine substitution to phenethylammonium for the organic cations to tune the structural rigidity and octahedral distortion yields a record exciton diffusivity of 1.91 cm2 s−1 and a diffusion length of 405 nm along the in‐plane direction.