A robust bicontinuous network for charge transport is a central requirement for efficient bulk heterojunction polymer solar cells. Factors affecting the network morphology include crystallinity and the relative concentration of the constituent materials. These factors are closely followed using a scanning approach which involves monitoring the photocurrent decay from the cathode-periphery in asymmetric device structures. The decay length correlates with the efficiency and the network connectivity of the ensuing microstructure. © 2012 American Institute of Physics.