Enhanced charge transport in hybrid polymer/ZnO-nanorod solar cells assisted by conductive small molecules
Control of interface properties is one of the important issues in optimizing the performance of hybrid polymer–metal-oxide solar cells. We select a soluble conductive small molecule, 2-naphthalenethiol (2-NT), to modulate the surface properties of the oriented ZnO-nanorod arrays before contacting with the polymer blend in an inverted hybrid solar cell configuration. This conductive molecule enhances the compatibility between polymer blend and metal-oxide, enlarges the exciton separation efficiency and subsequent charge transfer rate into the bulk of nanorods by the bond dipole field, reduces interfacial recombination and improves the ordering of charge transport network. As a result, there is a substantial improvement in photocurrent, open circuit voltage and fill factor leading to double the power conversion efficiency of the unmodified device from 1.86% to 3.71%. This value sets the record for the highest efficiency reported to date based on ITO/ZnO-nanorod/poly(3-hexythiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM)/Ag configuration.