Highly efficient organic solar cells enabled by ultraviolet-ozone treated molybdenum oxide hole transport layers

Abstract

The application of ultraviolet ozone (UV-Ozone) treatment of thermally evaporated molybdenum oxide (MoOx) as a hole transport layer (HTL) in non-fullerene acceptor (NFA)-organic solar cells (OSCs) has markedly improved the charge carrier transport. As a result, we report the power conversion efficiency (PCE) of PM6:Y6-based OSCs has been improved from 14.26% for pristine to 15.06% for UV-Ozone-treated devices. This PCE enhancement is attributed to increased hole mobility, more balanced mobilities ratio and higher direct current (DC) conductivity. Additionally, the formation of a more favourable interface between MoOx and the PM6:Y6 due to the UV-Ozone exposure, resulted in longer charge carrier lifetimes. Light soaking experiments at 55 °C in a nitrogen environment demonstrated superior operational stability with pristine and UV-Ozone-treated MoOx, retaining 58% and 65% of their initial PCE after 100 hours, respectively. This stands in contrast to devices based on PEDOT:PSS that deteriorated to 23% of their initial PCE after half the time period. This strategy is an enabler towards simultaneous improvement in performance and stability compared to the control PEDOT:PSS-based cells, presenting high efficiency but significantly lower lifetime stability. The broad applicability of UV-Ozone treatment of thermally evaporated MoOx HTLs was further validated through the fabrication of OSCs with a PM6:L8-BO photoactive layer, achieving a peak PCE value of 16.85%. These findings indicate significant advancements in the use of transition metal oxides in NFA-based OSCs and highlight the potential for new device architectures for organic electronics.