Charge transport in TiO₂/MEH-PPV polymer photovoltaics

Abstract

We study the effect of polymer thickness, hole mobility, and morphology on the device properties of polymer-based photovoltaics consisting of MEH-PPV as the optically active layer, TiO2 as the exciton dissociation surface, and ITO and Au electrodes. We demonstrate that the conversion efficiency in these polymerbased photovoltaics is primarily limited by the short exciton diffusion length combined with a low carrier mobility. For MEH-PPV devices with optimal device geometry, we achieve quantum efficiencies of 6% at the maximum absorption of the polymer, open circuit voltages of 1.1 V, current densities of 0.4 mA/cm2 and rectification ratios greater than 105 under 100 mW/cm2 white light illumination. In addition, we achieve fill factors up to 42% at high light intensities and as high as 69% at low light intensities. We conclude by presenting a model that describes charge transport in solid-state polymer/TiO2-based photovoltaics and suggest methods for improving energy conversion efficiencies in polymer-based photovoltaics.