Particle plasmon‐induced charge trapping at heterointerfaces in PCDTBT:PC₇₀BM blends

Abstract

We investigate the influence of particle plasmons on exciton and charge generation and recombination processes in the blend of poly (9-(1-octylnonyl)-9H-carbazolebenzothiadiazole-4,7-diyl-2,5-thiophenediyl) (PCDTBT) and [6,6]-phenyl-C 70 butyric acid methyl ester (PC 70 BM). The particle plasmons are generated from gold nanoparticles, which are embedded into PCDTBT:PC 70 BM blend. For the blend with gold nanoparticles, we observe enhance light harvesting. Despite the enhanced light collection, we find that the quasi-steady-state charge generation has not been influenced by the particle plasmons. However, the generation and recombination of long-lived (sub-millisecond) polaron paris have been significantly enhanced: from untrapped state in the pristine blend to the trapped state in the gold nanoparticle-embedded blend. This result implies that the plasmon-influenced polarons are trapped at the broadband geminate polaron pair (GPP) state. This state acts as an intermediate state, which either leads to the formation of charge transfer excitons (CTXs) or free charge carriers. In our case, the particle plasmon-influenced polarons are trapped in the GPP state, which leads to the formation of CTXs. For this reason, we do not observe the enhanced charge generation in PCDTBT:PC 70 BM blend with particle plasmon resonance. Finally, we revealed that the long-lived polarons mainly resulted from the localization by particle plasmons. The macroscopic modification in the blend film made negligible contributions to this influence. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 940-947