Photochemistry of P3HT and PC60BM in toluene solution: Evidence of T–T energy transfer

•Photochemistry of P3HT/PC60BM mixture in toluene was studied by laser flash photolysis.•Excitation of the mixture leads to energy transfer from polymer triplet state to fullerene.•Quantum yields of polymer and fullerene triplet state formation were estimated.•No evidence of electron transfer from P3HT triplet state to PC60BM was observed.

Photochemical properties of regioregular poly(3-hexylthiophene) (P3HT), fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) and their 1:1 mixture in argon-saturated toluene solution were studied by optical spectroscopy and nanosecond laser flash photolysis (λex = 532 nm). Separate excitation of components leads to formation of corresponding triplet state of fullerene (3PC60BM*, λmax = 710 nm, ϵmax = 22400 M−1 cm−1, φT = 0.29) and polymer (3P3HT*, λmax = 850 nm, ϵ750 nm ≤ 105 M−1 cm−1, φT ≥ 0.19). Excitation of P3HT/PC60BM mixture leads to effective energy transfer from 3P3HT* to the ground state of fullerene with a formation of 3PC60BM*. No evidence of ion-radical P3HT+ and PC60BM− formation was obtained though electron transfer between 3P3HT* and 1PC60BM is energetically favorable in studied system. Presumably ultrafast back electron transfer takes place in geminate P3HT+/PC60BM− pair with regeneration of the ground states of P3HT and PC60BM.

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