Self-Assembled Hole Transport Layer for Improving the Performance of Organic Photovoltaics

In this study, we introduce polymer-based self-assembled molecules as the hole transport layer (HTL) for the fabrication of organic photovoltaics. The poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3HT-COOH) is a wide bandgap conjugated polymer with carboxylic acid anchoring groups on the side chain of each thiophene repeat unit. The carboxylic acid group can bond to the In element of the indium-tin-oxide film and form a monolayer. We have successfully demonstrated that organic photovoltaics fabricated based on this self-assembled monolayer exhibit approximately 10% increase in power conversion efficiency in comparison with those using PEDOT:PSS as HTL. The improvement comes from the improved charge transport of the device. The details of the effect of the self-assembled monolayer on the performance of the devices will be discussed.