Acenaphthene-induced two-step crystallisation achieves record efficiency in binary organic solar cells

Prof. LI Gang, Chair Professor of Energy Conversion Technology and Sir Sze-yuen Chung Endowed Professor in Renewable Energy of the PolyU Department of Electrical and Electronic Engineering, and his research team have published a paper titled “Two-step crystallisation modulated through acenaphthene enabling 21% binary organic solar cells and 83.2% fill factor” in Nature Energy.

The crystallisation dynamics of non-fullerene acceptors influences the morphology and charge dynamics of organic solar cells, ultimately determining device performance.  However, optimising the molecular arrangement of donor and acceptor materials within the active layer remains a considerable challenge.  In this study, the research team controlled the crystallisation kinetics of non-fullerene acceptors with a crystallisation-regulating agent, acenaphthene.  Acenaphthene alters the self-organisation of acceptor molecules by inducing a two-step crystallisation process: it initially fixes the packing motif of the acceptor, and subsequently refines the crystallised framework, resulting in highly oriented acceptors within the active layer.

This approach establishes multiple charge-transport pathways, thereby enhancing the charge-transport properties of the device.  As a result, power conversion efficiencies of 20.9% (20.4% certified) and 21% (20.5% certified) were achieved in D18/L8-BO and PM1/L8-BO-X binary organic solar cells, respectively, with a maximum fill factor of 83.2% (82.2% certified).  These findings represent a significant advancement in the development of high-performance organic solar cells.

This innovative strategy paves the way for further breakthroughs in the efficiency and commercial viability of next-generation organic photovoltaic technologies.

Read the full paper: https://www.nature.com/articles/s41560-025-01862-1