Diffusion photovoltage in poly(p -phenylenevinylene)

Photovoltage phenomena in poly(p-phenylenevinylene) (PPV) are investigated under pulsed laser illumination. The photovoltage transients are strongly retarded in time depending on sample thickness, laser intensity, and bias illumination. It is shown that the photovoltage in PPV originates from separation of excess electrons and holes due to their concentration gradient and different diffusion coefficients (diffusion photovoltage). The diffusion coefficient of excess holes is found to be on the order of ${\text{1×10}}^{\text{−6}} {\mathrm{cm}}^{\mathrm{2}}\mathrm{/s}$ and it increases with increasing excitation intensity and intensity of bias illumination. The diffusion coefficient of excess electrons is about 1–2 orders of magnitude smaller than for excess holes.