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(C_3-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/C_3-SAM/CuⅠ/P3 HT:PC_(61)BM/ZnO/Al increased significantly from 2.55%(best 2.66%) to 3.04%(best 3.20%) after C_3-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.