Charge Carrier Transport, Recombination, and Trapping in Organic Solar Cells Studied by Double Injection Technique

In this paper, we demonstrate the possibilities of the double injection (DoI) current transient technique for the study of charge carriers´ transport, recombination, and trapping in thin organic solar cells (OSC). Numerically calculated DoI current transients were compared with the experimentally obtained current transients in regioregular poly(3-hexylthiophene) (RR-P3HT) and its blends with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). From coefficient of reduced Langevin recombination dependence on the density of charge carriers in the annealed PCBM/RR-P3HT bulk heterojunction, 2-D Langevin recombination was experimentally confirmed. Trapping of the electrons was observed in the samples of TiO₂/RR-P3HT and degraded blends of PCBM/RR-P3HT. The two injecting voltage pulses with delay between them have been used for determination of deep trapping states´ influence on charge carrier´s transport.