Self-assembled monolayer modified copper(I) iodide hole transport layer for efficient polymer solar cells

The morphology of the copper iodide (CuI) film as an inorganic p-type material has an important influence on enhancing the performance of polymer solar cells (PSCs). A self-assembled monolayer of 3-aminopropanoic acid (C₃-SAM) was used on the surface of indium tin oxide (ITO) before depositing the CuI films. Consequently, a well-distributed and smooth CuI film was formed with pinhole free and complete surface coverage. The root mean square of the corresponding CuI film was reduced from 3.63 nm for ITO/CuI to 0.77 nm. As a result, the average power conversion efficiency (PCE) of PSCs with the device structure of ITO/C₃-SAM/CuI/P3HT:PC₆₁BM/ZnO/Al increased significantly from 2.55% (best 2.66%) to 3.04% (best 3.20%) after C₃-SAM treatment. This work provides an effective strategy to control the morphology of CuI films through interfacial modification and promotes its application in efficient PSCs.