Bimolecular recombination in regioregular and regiorandom poly(3-hexylthiophene):PCBM using photoinduced absorption spectroscopy

We have used photoinduced absorption (PA) spectroscopy and measured the intensity dependence on thin films of 1: 1 blends of regioregular-poly(3-hexylthiophene): PCBM before and after annealing as well as on 1: 1 blends of regiorandom-poly(3-hexylthiophene): PCBM. We have calculated the bimolecular recombination coefficients from the out-of-phase component of the photoinduced absorption. Annealing shows no change in the bimolecular recombination coefficients of rr-P3HT: PCBM, but the increased PA amplitude suggests that the geminate (monomolecular) recombination is reduced. In rra-P3HT: PCBM, the bimolecular recombination coefficient estimated by the same method (disregarding dispersion) is significantly smaller, indicating together with a low PA amplitude that the recombination is primarily geminate. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of the European Material Research Society (E-MRS)