Improving voltage and quantum efficiency in blade-coated ITO-free organic solar cells processed with a non-halogenated solvent

Abstract

Developing ITO-free device structures, industrially compatible, and environmentally friendly fabrication processes is crucial for advancing organic solar cells (OSCs) technology toward commercialization. This study investigates the performance differences of ITO-free OSCs based on PM6:Y6, fabricated using three methods: spin-coating with chloroform (CF) solution, spin-coating with o-xylene (OXY) solution, and blade-coating with OXY solution. The findings reveal that the active layer prepared by blade-coating with OXY solution exhibits greater donor–acceptor phase separation and poorer molecular packing compared to the spin-coated CF solution, resulting in reduced exciton dissociation efficiency and inferior charge carrier transport. Additionally, the active layer blade-coated from OXY solution presents a higher density of trap states, leading to increased trap-assisted recombination, lower electroluminescence quantum efficiency (EQE_EL), and higher non-radiative voltage losses, which restrict the open-circuit voltage (V_OC) of the devices. To mitigate these performance losses, we introduce an acceptor side chain modification strategy to improve the morphology and structural order of the active layer, thereby enhancing exciton dissociation efficiency and reducing the density of trap states. This results in significant improvements in both short-circuit current density (J_SC) and V_OC. Using the Y6DT acceptor as an example, the performance of ITO-free OSCs fabricated by blade-coating with OXY solution deliver a power conversion efficiency (PCE) of 13.5%.