Diketopyrrolopyrrole-based small molecule for application in solution processed organic solar cells

A novel donor-π bridge - acceptor (A)-π bridge - donor type molecule (PCTDPP20) with planar core based on diketopyrrolopyrrole (DPP) and carbazole is synthesized by the Suzuki coupling reaction. We introduce phenyl rings to extend the π-conjugation length as a π-bridge. The HOMO and LUMO energy levels of PCTDPP20 are -5.13 and -3.57 eV, respectively. From the UV-Vis spectra, we confirm that the maximum absorption wavelgth (λ_max) of the PCTDPP20 annealed film at 100°C is red-shifted about 30 nm and the absorption intensity at 600 ∼ 650 nm increase compared to that of as-spun film. And the OFET based on PCTDPP20 annealed at 100°C exhibits a highest hole mobility of 1.6 × 10^-4 cm²/Vs together with a Ion/Ioff ratio of 1.0 × 104 and a Vth of 14 V. Also, the photovoltaic properties are investigated in the device structure of ITO/PEDOT:PSS/PCTDPP20:PC₆₀BM (with different blend ratios)/Al. Among the OSCs, PCTDPP20:PCBM weight ratio of 1:0.8 and termal annealing process at 100°C for 10 min are optimum belnd ratio and temperature, respectively. This device shows the best performance with a highest PCE of 0.95% a Jsc of -2.69 mA/cm², a Voc of 0.79 V and a fill factor of 44.5%.