Two-step crystallization modulated through acenaphthene enabling 21% binary organic solar cells and 83.2% fill factor

Abstract

The crystallization dynamics of non-fullerene acceptors influences the morphology and charge dynamics of the resulting organic solar cells, ultimately determining device performance. However, optimizing the molecular arrangement of donor and acceptor materials within the active layer remains challenging. Here we control the crystallization kinetics of non-fullerene acceptors with a crystallization-regulating agent, acenaphthene. Acenaphthene changes the self-organization of acceptor molecules by inducing a two-step crystallization: it first fixes the packing motif of the acceptor and then refines the crystallized framework, leading to highly oriented acceptors in the active layer. This forms several charge-transport pathways that improve the charge-transport properties of the device. As a result, efficiencies of 20.9% (20.4% certified) and 21% (20.5% certified) are 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). The result is a step forward in the development of organic solar cells. Optimizing the crystallization of the active materials in organic solar cells is challenging. Fu et al. use an acenaphthene additive to induce a two-step crystallization of the non-fullerene acceptor, achieving a certified 20.5% power conversion efficiency.