Ultrafast Photoinduced Charge Separation Dynamics in Polythiophene/SnO2 Nanocomposites

Abstract

We present a study of photoinduced interfacial electron transfer (ET) dynamics of SnO₂ nanocrystalline thin films sensitized by polythiophene derivatives (regioregular poly(3-hexylthiophene) (P3HT) and regiorandom poly(3-undecyl-2,2‘-bithiophene) (P3UBT)). ET dynamics were measured by following the dynamics of injected electrons in SnO₂ and polarons in the conjugated polymer using ultrafast mid-IR transient absorption spectroscopy. The rate of electron transfer from P3HT and P3UBT to SnO₂ films was determined to occur on sub-picosecond time scale (120 ± 20 fs). In P3HT/SnO₂ composite, interchain charge transfer was found to compete with and reduce the quantum efficiency of interfacial electron transfer at high polymer loading. This interchain charge separation processes can be reduced in non-regioregular polymer or at low polymer loading levels.