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

Abstract

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 (lambda(ex) = 532 nm). Separate excitation of components leads to formation of corresponding triplet state of fullerene ((PC60BM)-P-3*, lambda(max) = 710 nm, epsilon(max) = 22400 M-1 cm(-1), phi(T) = 0.29) and polymer ((3)P3HT*, lambda(max) = 850 nm, epsilon(750 nm) <= 10(5) M-1 cm(-1), phi(T) >= 0.19). Excitation of P3HT/PC60BM mixture leads to effective energy transfer from (3)P3HT* to the ground state of fullerene with a formation of (PC60BM)-P-3*. No evidence of ion-radical P3HT(+center dot) and PC60BM-center dot formation was obtained though electron transfer between (3)P3HT* and (PC60BM)-P-1 is energetically favorable in studied system. Presumably ultrafast back electron transfer takes place in geminate P3HT(+center dot)/PC60BM-center dot pair with regeneration of the ground states of P3HT and PC60BM. (C) 2015 Elsevier B.V. All rights reserved.