Oligothiophene-modified silver/silica core–shell nanoparticles for inhibiting open-circuit voltage drop and aggregation in polymer solar cells

Abstract

Metal nanoparticles (NPs) have attracted much attention owing to their particular characteristics such as localized surface plasmon resonance (LSPR) and scattering properties, which can improve the light-harvesting ability of photovoltaic cells. However, modification of the metal NP surface is needed to prevent particle aggregation and photoinduced charge trapping. Surface modification of silica-coated Ag NPs with oligothiophene (OT) provides silver/silica core–shell (Ag@SiO₂–OT) NPs, which are well dispersed in nonpolar organic solvents and miscible with the bulk-heterojunction (BHJ) layer of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) (P3HT:PCBM). Incorporation of the Ag@SiO₂–OT NPs into the P3HT:PCBM layers as the active layer of photovoltaic devices improves the light-harvesting ability and enhances the photo-conversion efficiency (PCE) by about 18%. There is no significant change in the open-circuit voltage (V_oc) value even when up to 30 wt% of Ag@SiO₂–OT NPs are incorporated, confirming that the OT-modified silica layer on silver NPs contributes to improving light absorption and photo-current without causing aggregation and photo-induced charge trapping. Moreover, the deliberately designed transmission electron microscopy (TEM) investigation of the composite films of P3HT:PCBM and Ag@SiO₂–OT NPs reveals that Ag@SiO₂–OT NPs are mainly located in the P3HT domain owing to the favorable interaction between the similar molecular structures of OT and P3HT.