Triplet Formation by Charge Recombination in Thin Film Blends of Perylene Red and Pyrene: Developing a Target Model for the Photophysics of Organic Photovoltaic Materials

Photoinduced charge separation in a mixture of Perylene Red (N,N′-bis(2,6-di-isopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxylic acid bis-imide) and pyrene, organized in thin solid film on quartz, was studied by means of steady-state absorption and emission spectroscopy and by femtosecond transient absorption spectroscopy. Steady state spectroscopy shows substantial interaction between the two chromophores in the ground and excited states. Luminescence quenching indicates charge transfer interaction. Global and target analysis of the transient absorption data indicates a complex photophysical behavior with the formation of long-lived charges (free charge carriers) and of a triplet excited state species (with rates of ∼10.4 × 109 and 72.1 × 106 s-1) via charge recombination pathways from charged states. A generally applicable target model for the analysis of photophysical data of photovoltaic blends is developed.