Improved efficiency of solar cells based on BEHP-co-MEH-PPV doped with ZnO nanoparticles

Abstract

Organic photovoltaic cells are made by sandwiching a composite active layer of organic electronic materials conjugated copolymer (BEHP-co-MEH-PPV) mixed with ZnO nanoparticles, between two metallic conductors, typically a layer of indium tin oxide (ITO) with high work function (4.8eV) and a layer of low work function metal (3.7eV) such as aluminium. In this work, the spin coated conjugated copolymer blends (BEHP-co-MEH-PPV): ZnO thin films, deposited on both silicon and glass substrates, have been studied for morphology using atomic force microscopy (AFM). All films examined by AFM, showed a dense structure with average roughness of 20–40nm.Optical properties were explored for films coated onto glass substrates at a spin speed of 1200rpm, using a spectrophotometer for optical absorption in the visible region. The photo luminescence (PL) spectra of the pure and blended BEHP-co-MEH-PPV films were recorded. Ellipsometry were used for refractive index, extinction coefficient and thickness. The current–voltage characteristics (I–V's) of the solar cell showed that incorporation of the ZnO nanoparticles in the copolymer resulted into further increase in the power conversion efficiency compared to that in their absence.All deposited films showed good adhesion to substrates, and good optical properties. The conductivity of the active layer increases with the increment of the ZnO nanoparticles into the nanocomposite thin films. Such characteristics make the copolymer: nanoparticle blended layer (BEHP-co-MEHPPV: ZnO) very favourable to charge injection and conduction for photovoltaic devices.