Critical Role of Polystyrene Layer on Plasmonic Silver Nanoplates in Organic Photovoltaics

Abstract

Plasmonic nanoparticles create large local electric field enhancements in organic photovoltaics (OPVs), substantially enhance the absorption of light, and consequently improve the device efficiency. In this report, anisotropic Ag nanoplates (AgNPs) were functionalized by thiol-terminated polystyrene (PS-SH) to yield polystyrene-functionalized Ag nanoplates (PS-AgNPs). The PS-AgNPs were spin-coated directly on the OPV active layer, poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM). A systematic variation of the PS-AgNP solution concentration correlated to different nanoparticle densities on the active layer. The localized surface plasmon resonance (LSPR) of the PS-AgNPs enhanced the light absorption of the active layer, which directly contributed to an increase in exciton yield, demonstrated by the increased photoluminescence emission intensities in P3HT films. In addition, incorporation of the PS-AgNPs decreased the series resistance and increased the photocurrent of the devices. In devices with PS-AgNP at a concentration of 0.57 nM, the power conversion efficiency was 32% higher than the devices without the PS-AgNPs. Without the polystyrene functionalization, however, the AgNPs severely deteriorated the performance of the OPV devices regardless of the nanoparticle concentration.