The measured photocurrent ofa solar cell may be considered the sum ofa photo-generated current due solely to the influx of photons, and a photovoltage-induced current that is injected at the electrodes. Correcting the measured photocurrent for the dark current yields the voltage dependence of the photogenerated current alone. This corrected photocurrent can provide important insight into the processes governing the behaviour of a solar cell, yet is seldom measured or discussed within the community. In this dissertation, an original experimental technique designed specifically for the reliable measurement of the corrected photocurrent is described, with the intent of applying it to the study of solar cells based on thin films ofblended donor and acceptor molecular semiconductor pairs otherwise known as organic bulk-heterojunction solar cells. Solar cells based on a number of donor-acceptor combinations were investigated. Using the experimental technique developed here, corrected photocurrent-voltage responses exhibiting remarkably anti-symmetric profiles were obtained and subsequently rationalised with a simple physical model presented in this thesis. From the perspective of this model, the nature of charge extraction at the electrodes - and how this was affected by thermally annealing the device - was examined. Finally, a new low band gap, small-molecule acceptor material was used in bulkheterojunction solar cells, which showed promising photovoltaic performance. However, these devices exhibited anomalous behaviour that was observed in their current-voltage characteristics, which on closer examination, could be explained by electric field dependence in the photogeneration rate. Throughout this work, particular attention was given to the impact of these findings on how device efficiencies may be improved.