Toward Quantifying the Relation between Exciton Binding Energies and Molecular Packing

Miaofei Huang; Taiping Hu; Guangchao Han; Chao Li; Lingyun Zhu; Jiadong Zhou; Zengqi Xie; Yanming Sun; Yuanping Yi

doi:10.1021/acs.jpclett.2c03043

Toward Quantifying the Relation between Exciton Binding Energies and Molecular Packing

J Phys Chem Lett. 2022 Dec 8;13(48):11065-11070. doi: 10.1021/acs.jpclett.2c03043. Epub 2022 Nov 23.

Authors

Miaofei Huang^{1

2}, Taiping Hu¹, Guangchao Han¹, Chao Li³, Lingyun Zhu⁴, Jiadong Zhou⁵, Zengqi Xie⁵, Yanming Sun³, Yuanping Yi^{1

2}

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, China.
² University of Chinese Academy Sciences, Beijing 100049, China.
³ School of Chemistry, Beihang University, Beijing 100191, China.
⁴ CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China.
⁵ State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and Devices, Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates, South China University of Technology, 510640 Guangzhou, China.

PMID: 36416780
DOI: 10.1021/acs.jpclett.2c03043

Abstract

Reducing the exciton binding energy E_b of organic photoactive materials is critical to minimize the energy loss and improve the photovoltaic efficiency of organic solar cells. However, the relation between the E_b and molecular packing is not well understood. Herein, the E_b in the crystals of a series of A-D-A type nonfullerene acceptors with different lengths of alkyl side chains has been examined by self-consistent quantum mechanics/embedded charge calculations. The variation of molecular packing induced by the different alkyl chains can have an important impact on the polarization effect of charge carriers and thereby the E_b. More interestingly, the E_b values are found to be linearly increased with the ratio of the void fraction vs the packing coefficient of molecular backbones in the solid crystals. Owing to the smallest ratio, a remarkable low E_b of several tens of meV is achieved for the acceptor with an optimal length of alkyl chains.