Enhanced photovoltaic performance of inverted polymer solar cells by incorporating graphene nanosheet/AgNPs nanohybrids

Abstract

A linear-dendritic block copolymer (LDBC) functionalized exfoliated graphene nanosheets (XGS)/silver nanoparticles (AgNPs) was prepared for using as the interfacial layer between the zinc oxide (ZnO) based electron-selective layer and poly(3-hexylthiophene) (P3HT)/fullerene derivative (PC₆₁BM) blend based photoactive layer in an inverted polymer solar cell (PSC). The LDBCs were prepared by the respective addition reaction of a hydrophilic poly(oxyalkylene)amine with hydrophobic dendrons of various generations based on 4-isocyanate-4′-(3,3-dimethyl-2,4-dioxo-azetidine)-diphenylmethane (IDD). The dendrons having polyurea/malonamide functionalities were synthesized by using IDD as a building block. Moreover, the dendrons comprised not only hydrogen bond-rich malonamide linkages, but long alkyl chains at the peripheries as well. XGS were respectively grafted with these amphiphilic LDBCs to afford XGS-dendritic derivatives (XGS-G0.5, XGS-G1.5, and XGS-G2.5). Subsequently, a nanohybrid, XGS-G2.5/AgNPs was obtained through the reduction of Ag⁺ on the surface of LDBC modified XGS. The dendrons would serve as the effective templates for hosting AgNPs. By the incorporation of XGS-G2.5/AgNPs nanohybrid, it rendered the PSC an increased power conversion efficient (PCE) to 4.04%, a 19.5% improvement over a PCE of 3.38% for the bare inverted PSC, due to the localized surface plasmon resonance of AgNPs, and the improvement of compatibility and charge transfer capacity between ZnO based cathode and photoactive layer.