Thickness dependent red shift of the photocurrent spectrum in bulk heterojunction solar cells

摘要

Photocurrent spectra are measured for two different types of bulk heterojunction organic solar cells having a range of active layer thicknesses. Normalized by the number of incident photons, the photocurrent peak red shifts with respect to the absorption maximum as the sample thickness increases. Comparison to photocurrent measurements made with a chopped light source shows that the shift is due to an increased contribution from long wavelength absorption in the central active region. Fitting the thickness dependent photocurrent to a charge recombination model provides a measure of carrier collection lengths and surface recombination.