Analytical model for the photocurrent-voltage characteristics of bilayer MEH-PPV/TiO 2 photovoltaic devices

The photocurrent in bilayer polymer photovoltaic cells is dominated by the exciton dissociation efficiency at donor/acceptor interface. An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO 2 photovoltaic cells. The model gives an analytical expression for the exciton dissociation efficiency at the interface, and explains the dependence of the photocurrent of the devices on the internal electric field, the polymer and TiO 2 layer thicknesses. Bilayer polymer/TiO 2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO 2 , with different thicknesses of the polymer and TiO 2 films, were prepared for experimental purposes. The experimental results for the prepared bilayer MEH-PPV/TiO 2 cells under different conditions are satisfactorily fitted to the model. Results show that increasing TiO 2 or the polymer layer in thickness will reduce the exciton dissociation efficiency in the device and further the photocurrent. It is found that the photocurrent is determined by the competition between the exciton dissociation and charge recombination at the donor/acceptor interface, and the increase in photocurrent under a higher incident light intensity is due to the increased exciton density rather than the increase in the exciton dissociation efficiency.