Size effects of metal nanoparticles embedded in a buffer layer of organic photovoltaics on plasmonic absorption enhancement

Abstract

The effects of Au or Ag nanoparticles on optical absorption enhancement of organic photovoltaics based on blended poly(3-hexylthiophene) : phyenyl-C61-butyric acid methyl ester (P3HT : PCBM) were investigated using a finite-difference-time-domain method. The spherical metal nanoparticles were embedded in a buffer layer of thickness 20 nm and their size was varied from 10 to 50 nm. The metal nanoparticles with diameter 10–20 nm offered negligible absorption enhancement in the active layer. Unlike those short metal nanoparticles, the incorporation of metal nanoparticles taller than the buffer layer led to a significant absorption enhancement by plasmonic resonance especially in the case of Ag nanoparticles. Ag nanoparticles gave broader and stronger absorption enhancement in the active layer than Au nanoparticles. An enhancement of 34% in the optical absorption of the active layer was observed with Ag nanoparticles of 50 nm diameter at 10% coverage. The electric field distributions around metal nanoparticles, their self-absorption and the active layer thickness dependence on the absorption enhancement were studied.