Synthesis, photophysical and photovoltaic properties of star-shaped molecules with triphenylamine as core and phenylethenylthiophene or dithienylethylene as arms

Two solution-processable star-shaped compounds, P and T ,that contain triphenylamine as core and phenylethenylthiophene or dithienylethylene, respectively, as arms were synthesized. They carry also a cyano group on the vinylene bond in the arms. These compounds showed an excellent thermal stability and relatively low (66–72 °C) glass transition temperatures. Their UV–vis spectra showed maximum at 431–459 nm with optical band gaps of 2.22–2.41 eV. They behaved as yellow-orange light emitters with photoluminescence (PL) maximum at 521–610 nm. The PL maximum of T was red shifted relative to P. Photovoltaic devices with active layers based on P (or T) and PCBM were prepared and the thin film composition and the thermal annealing treatment were screened in order to optimize the performance of the devices. The morphology of the blend films and the hole mobilities of P and T were also investigated. Photovoltaic performances of the devices with blend film containing 50 wt%/PCBM in P and T showed highest power conversion efficiencies (PCEs) 0.29% and 0.41%, respectively.