High-performance all-small-molecule organic solar cells without interlayers

In this work, we report a two-step solvent treatment (TSST) strategy to construct high-performance all-small-molecule solar cells (all-SMSCs) without interfacial layers (IFLs), which only consist of an active layer (AL) sandwiched between two electrodes. The chlorinated ITO (ITO-Cl) anode exhibits down-shifted work functions and improved surface energy enabled by the presence of a large density of chloride ions caused by the surface chlorination of ITO. Moreover, the Al cathode shows elevated vacuum level and reduced interfacial trap density enabled by surface treatment of the active layer with polar methanol. The ITO-Cl/AL/Al-based devices form Ohmic contacts and boost the efficiency of the B1:BTP-eC9 system to 14.86%, which is higher than that of the control device (13.92%) with two IFLs. The use of this TSST strategy in the other two all-small-molecule systems is also confirmed, demonstrating its good generality. This strategy can significantly improve device stabilities, extend the life cycles of ITO substrates, and reduce modules' production costs.