Trap-limited bimolecular recombination in poly(3-hexylthiophene): Fullerene blend films

Trap-limited bimolecular recombination in poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blend films has been investigated by using photo-induced charge extraction by linearly increasing voltage (photo-CELIV) method. The bimolecular recombination rate is strongly dependent on the photoexcitation density, the PC61BM composition and the thermal annealing process, but it slightly depends on the thickness of the blend film. The results show that the trap-limited bimolecular recombination is strongly affected by the distribution of the density of trap state (trap DOS). The higher trap-limited bimolecular recombination rate means the trap DOS centered at lower energy which is beneficial to charge carriers transportation, due to the lower activation energy and faster release rate. On the other hand, the trap-limited bimolecular recombination rate is mainly controlled by the slower species of charge carriers in the blend film when the transport of electrons and holes are strongly unbalanced, and the recombination rate will increase when the transport of electrons and holes becomes more balanced. (C) 2016 Elsevier B.V. All rights reserved.