Self-assembled monolayer modified copper(I) iodide hole transport layer for efficient polymer solar cells**Project supported by the National Natural Science Foundation of China (Grant Nos. 61377065 and 61574064), the Science and Technology Planning Project of Guangdong Province, China (Grant Nos. 2013CB040402009 and 2015B010132009), and the Science and Technology Project of Guangzhou City, China (Grant No. 2014J4100056).

Abstract

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.