Simultaneous enhancement of photocurrent and open circuit voltage in a ZnO based organic solar cell by mixed self-assembled monolayers

In this study, we utilized the carboxylic acid functionalized molecules, namely, benzoic acid (BZA) and C61-dicarboxylic acid (CDCA) as interfacial modifiers to form self-assembled monolayers (SAM) in polymer hybrid solar cell (HSC) consisting of poly (3-hexylthiophene) (P3HT) and zinc oxide (ZnO). We found that the short circuit current density (Jsc) and the open circuit voltage (Voc) of the device could be drastically increased by using CDCA-SAM and BZA-SAM, respectively. On the other hand, the optimized mixture of CDCA-SAM and BZA-SAM showed better improvement in both the Jsc and Voc. The devices modified with mixed SAMs in an optimized ratio showed significant increment in the overall conversion efficiencies compared to unmodified devices consisting of both bi-layer and nanorod (NR) structured HSC. In particular, almost 1.2-fold improvement could be achieved on the NR device with the efficiencies of 0.73%. We attribute the improvement of Jsc and Voc to higher carrier mobility of CDCA-SAM and work function modulation of ZnO by BZA-SAM, respectively.