Issue 1, 2024

Molecularly induced order promotes charge separation through delocalized charge-transfer states at donor–acceptor heterojunctions

Abstract

The energetic landscape at the interface between electron donating and accepting molecular materials favors efficient conversion of intermolecular charge-transfer (CT) states into free charge carriers (FCC) in high-performance organic solar cells. Here, we elucidate how interfacial energetics, charge generation and radiative recombination are affected by molecular arrangement. We experimentally determine the CT dissociation properties of a series of model, small molecule donor–acceptor blends, where the used acceptors (B2PYMPM, B3PYMPM and B4PYMPM) differ only in the nitrogen position of their lateral pyridine rings. We find that the formation of an ordered, face-on molecular packing in B4PYMPM is beneficial to efficient, field-independent charge separation, leading to fill factors above 70% in photovoltaic devices. This is rationalized by a comprehensive computational protocol showing that, compared to the more amorphous and isotropically oriented B2PYMPM, the higher structural order of B4PYMPM molecules leads to more delocalized CT states. Furthermore, we find no correlation between the quantum efficiency of FCC radiative recombination and the bound or unbound nature of the CT states. This work highlights the importance of structural ordering at donor–acceptor interfaces for efficient FCC generation and shows that less bound CT states do not preclude efficient radiative recombination.

Graphical abstract: Molecularly induced order promotes charge separation through delocalized charge-transfer states at donor–acceptor heterojunctions

Supplementary files

Article information

Article type
Communication
Submitted
06 Apr 2023
Accepted
09 Oct 2023
First published
25 Oct 2023

Mater. Horiz., 2024,11, 173-183

Molecularly induced order promotes charge separation through delocalized charge-transfer states at donor–acceptor heterojunctions

X. Jia, L. Soprani, G. Londi, S. M. Hosseini, F. Talnack, S. Mannsfeld, S. Shoaee, D. Neher, S. Reineke, L. Muccioli, G. D’Avino, K. Vandewal, D. Beljonne and D. Spoltore, Mater. Horiz., 2024, 11, 173 DOI: 10.1039/D3MH00526G

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