Double-injection current transients as a way of measuring transport in insulating organic films

We propose a double-injection current transient technique for the study of charge-carrier transport in thin insulating films of low-mobility materials with reduced carrier bimolecular recombination compared to the Langevin type. This experimentally simple technique, allows us to estimate the sum of the faster carrier and the slower carrier mobility's (μf + μs) and the slower carrier mobility (μs). Furthermore, in thin films when the RC current overlaps the injection current transients we propose to estimate these transport parameters using the extracted charge as a function of injection pulse duration. The method is applied on bulk-heterojunction solar cells made from blends of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]- methanofullerene. We have experimentally verified the technique by measuring the charge carrier mobility's and compared them with results obtained using standard time-of-flight and carrier extraction using linearly increasing voltage techniques.