Charge transport in hybrid nanorod-polymer composite photovoltaic cells

Charge transport in composites of inorganic nanorods and aconjugated polymer is investigated using a photovoltaic device structure.We show that the current-voltage (I-V) curves in the dark can be modelledusing the Shockley equation modified to include series and shuntresistance at low current levels, and using an improved model thatincorporates both the Shockley equation and the presence of a spacecharge limited region at high currents. Under illumination, theefficiency of photocurrent generation is found to be dependent on appliedbias. Furthermore, the photocurrent-light intensity dependence was foundto be sublinear. An analysis of the shunt resistance as a function oflight intensity suggests that the photocurrent as well as the fill factoris diminished as a result of increased photoconductivity of the activelayer at high light intensity. By studying the intensity dependence ofthe open circuit voltage for nanocrystals with different diameters andthus ! band gaps, it was inferred that Fermi-level pinning occurs at theinterface between the aluminum electrode and the nanocrystal.