Photoinduced Carrier Generation and Recombination Dynamics of a Trilayer Cascade Heterojunction Composed of Poly(3-hexylthiophene), Titanyl Phthalocyanine, and C60

We use flash-photolysis time-resolved microwave conductivity experiments (FP-TRMC) and femtosecond-nanosecond pump-probe transient absorption spectroscopy to investigate photoinduced carrier generation and recombination dynamics of a trilayer cascade heterojunction composed of poly(3-hexylthiophene) (P3HT), titanyl phthalocyanine (TiOPc), and fullerene (C₆₀). Carrier generation following selective photoexcitation of TiOPc is independently observed at both the P3HT/TiOPc and TiOPc/C₆₀ interfaces. The transient absorption results indicate that following initial charge generation processes to produce P3HT^•+/TiOPc^•- and TiOPc^•+/C₆₀^•- at each interface from (P3HT/TiOPc/C₆₀), the final charge-separated product of (P3HT^•+/TiOPc/C₆₀^•-) is responsible for the long-lived photoconductance signals in FP-TRMC. At the P3HT/TiOPc interface in both P3HT/TiOPc and P3HT/TiOPc/C₆₀ samples, the electron transfer appears to occur only with the crystalline (weakly coupled H-aggregate) phase of the P3HT.