Enhanced Photogeneration of Triplet Excitons in an Oligothiophene–Fullerene Blend

Abstract

Photoinduced and transient absorption spectroscopy is used to study triplet exciton dynamics in thin films of a new thiophene‐based oligomer (DCV3T) and blends of DCV3T and fullerene C₆₀. We find enhanced DCV3T triplet exciton generation in the blend layer, which is explained as an excitonic ping–pong effect: singlet energy transfer from DCV3T to C₆₀, followed by immediate intersystem crossing to C₆₀, and triplet exciton back‐transfer. Estimations of the rate constants involved show that the ping–pong effect has an overall efficiency close to unity. The singlet–singlet energy transfer from DCV3T to C₆₀ is demonstrated by efficient quenching of DCV3T luminescence in the blend, leading to sensitized emission of C₆₀. We discuss a promising new concept of solar cells with an enlarged active‐layer thickness based on potentially long‐ranged triplet exciton diffusion in combination with efficient intersystem crossing.