Ferrocene as a highly volatile solid additive in non-fullerene organic solar cells with enhanced photovoltaic performance

At present, most of the top-performing organic solar cells (OSCs) are processed with high boiling point solvent additives, which usually have a negative effect on the device stability. To overcome this conundrum, we herein introduce a commercially available organic transition metal compound, ferrocene, as a highly volatile solid additive in OSCs. The utilization of ferrocene led to enhanced power conversion efficiency (PCE) and photostability of PM6:Y6 based OSCs in comparison with the devices processed with a traditional solvent additive. Systematic analysis revealed that the treatment with ferrocene can effectively increase the molecular crystallinity and thus leads to improved charge transport, which accounts for the achieved higher photovoltaic performance in the corresponding OSCs. Moreover, ferrocene was found to exhibit general applicability in five other bulk-heterojunction systems. This work not only demonstrates a cost effective and highly volatile solid additive, but also opens a new possibility toward further improvement of the PCE and stability of OSCs.