Charge carrier dynamics in small-molecule- and polymer-based donor-acceptor blends

We present a comparative study of optical absorption, photoluminescence (PL), and photoconductivity in bulk heterojunctions comprising a high performance functionalized anthradithiophene (ADT) derivative or the benchmark polymer P3HT as donor and functionalized pentacene (Pn) derivative or PCBM as acceptor. Of all D/A blends studied, the ADT/PCBM blend exhibited the highest charge photogeneration efficiencies under 532 nm excitation, leading to the highest amplitudes of time-resolved and continuous wave (cw) photocurrents. At nanosecond time scales after photoexcitation, both ADT-TES-F-based blends and the P3HT/Pn-TIPS-F8 blend exhibited photocurrents which were higher by a factor of 2-10, depending on the blend, than that in the P3HT/PCBM blend. However, cw photocurrents showed a different trend, with the ADT-TES-F/PCBM blend exhibiting only a factor of ∼2.5 higher photoresponse than that in the P3HT/PCBM blends, and the ADT-TES-F- and P3HT- based blends with Pn-TIPS-F8 showing a factor of ∼1.5-2.5 lower photoresponse than that in the P3HT/PCBM blend, due to other contributions, such as that of charge trap-limited transport, to cw photoresponse.