The role of interfacial donor-acceptor percolation in efficient and stable all-polymer solar cells

Zhen Wang; Yu Guo; Xianzhao Liu; Wenchao Shu; Guangchao Han; Kan Ding; Subhrangsu Mukherjee; Nan Zhang; Hin-Lap Yip; Yuanping Yi; Harald Ade; Philip C Y Chow

doi:10.1038/s41467-024-45455-0

The role of interfacial donor-acceptor percolation in efficient and stable all-polymer solar cells

Nat Commun. 2024 Feb 8;15(1):1212. doi: 10.1038/s41467-024-45455-0.

Authors

Zhen Wang¹, Yu Guo¹, Xianzhao Liu¹, Wenchao Shu², Guangchao Han², Kan Ding³, Subhrangsu Mukherjee³, Nan Zhang⁴, Hin-Lap Yip^{4

5

6}, Yuanping Yi², Harald Ade³, Philip C Y Chow⁷

Affiliations

¹ Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
² CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Haidian, Beijing, 100190, China.
³ Department of Physics and Organic and Carbon Electronics Laboratories (ORaCEL), North Carolina State University, Raleigh, NC, 27695, USA.
⁴ Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong SAR, China.
⁵ School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong SAR, China.
⁶ Hong Kong Institute for Clean Energy, City University of Hong Kong, Kowloon, Hong Kong SAR, China.
⁷ Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China. pcyc@hku.hk.

Abstract

Polymerization of Y6-type acceptor molecules leads to bulk-heterojunction organic solar cells with both high power-conversion efficiency and device stability, but the underlying mechanism remains unclear. Here we show that the exciton recombination dynamics of polymerized Y6-type acceptors (Y6-PAs) strongly depends on the degree of aggregation. While the fast exciton recombination rate in aggregated Y6-PA competes with electron-hole separation at the donor-acceptor (D-A) interface, the much-suppressed exciton recombination rate in dispersed Y6-PA is sufficient to allow efficient free charge generation. Indeed, our experimental results and theoretical simulations reveal that Y6-PAs have larger miscibility with the donor polymer than Y6-type small molecular acceptors, leading to D-A percolation that effectively prevents the formation of Y6-PA aggregates at the interface. Besides enabling high charge generation efficiency, the interfacial D-A percolation also improves the thermodynamic stability of the blend morphology, as evident by the reduced device "burn-in" loss upon solar illumination.