Charge transport in TiO2/MEH-PPV polymer photovoltaics - art. no. 125205

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, an d ITO and Au electrodes. We demonstrate that the conversion efficiency in t hese polymer-based 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/cm(2) and rectification ratios greater than 10(5) under 100 mW/cm(2) white light illumination. In addition, we achieve fill factor s up to 42% at high light intensities and as high as 69% at low light inten sities. We conclude by presenting a model that describes charge transport i n solid-state polymer/TiO2-based photovoltaics and suggest methods for impr oving energy conversion efficiencies in polymer-based photovoltaics.