Additive-assisted molecular aggregation manipulation towards efficient thick organic solar cells

Developing thickness-insensitive organic solar cells (OSCs) is of vital importance for meeting the requirements of the mass production of solar panels. Herein, the molecular aggregation behaviour of non-fullerene acceptors was manipulated via two different solvent additives, namely, 1-phenylnaphthalene (PN) and 1-chloronaphthalene (CN), to improve the charge transport in thick OSCs. The planar structure of the naphthalene ring coupled with large phenyl steric hindrance allows the PN additive to insert into the adjacent N3 molecules, disturbing their face-to-face pi-pi stacking and enhancing the J-aggregation in the blends. As a result, the PN-treated blend film exhibits red-shifted and broad absorption as well as increased charge carrier mobility, which is crucial for high-performance thick OSCs. In contrast, the CN additive, with a small side group possessing good solubility for N3 and a high boiling point, facilitates the H-type aggregation of acceptors in the spin-coating process. With the incorporation of 0.5 vol% PN, the 120-nm-thick D18-Cl:N3-based devices obtained a power conversion efficiency (PCE) over 18.0%, significantly higher than the 16.22% and 16.08% for the control and CN-treated devices, respectively. Impressively, when the active layer thickness is increased to 300 nm, the resultant device still obtained a PCE of 16.48%. This work provides a simple additive strategy to facilitate the precise control of molecular aggregation during the film formation process for high-performance thick OSCs. The additive 1-phenylnaphthalene (PN) with large steric hindrance is used to promote J-aggregation of N3 molecules, which is conductive to broadening absorption spectra and improving charge transport for high-performance thick OSCs.