New conjugated molecules with two and three dithienyldiketopyrrolopyrrole (DPP) moieties substituted at meta positions of benzene toward p- and n-type organic photovoltaic materials

Two conjugated molecules, TADPP3 and TADPP2-TT, are reported, in which three and two dithienyldiketopyrrolopyrrole (DPP) moieties, respectively, are substituted at the meta positions of benzene. Based on cyclic voltammetry and absorption data, TADPP3 and TADPP2-TT possess similar HOMO and LUMO energies of about -5.2 and -3.4 eV, respectively. Thin films of TADPP3 and TADPP2-TT exhibit p-type semiconducting behavior with hole mobilities of 2.36×10 ^-3 and 3.76×10^-4 cm² V^-1 s^-1 after thermal annealing. Molecules TADPP3 and TADPP2-TT were utilized as p-type photovoltaic materials to fabricate organic solar cells after blending with phenyl C₇₁ butyric acid methyl ester (PC ₇₁BM) and phenyl C₆₁ butyric acid methyl ester (PC ₆₁BM). The relatively low J_SC and fill factor values can be attributed to poor film morphologies based on AFM and XRD studies. A solar cell with a thin film of TADPP3 with PC₇₁BM in a weight ratio of 1:2 exhibits a high open-circuit voltage (V_OC) of 0.99 V and a power conversion efficiency (PCE) of 2.47 %. Interestingly, TADPP3 can also be employed as an n-type photovoltaic material. The blended thin film of TADPP3 with P3HT in a weight ratio of 1:2 gave a high V_OC of 1.11 V and a PCE of 1.08 % after thermal annealing. Star-shaped small molecules: Two conjugated molecules, TADPP3 and TADPP2-TT, have been developed and applied in solution-processed organic solar cells. Molecule TADPP3 can be applied as both a donor and an acceptor. The resulting solar cells have a high open-circuit voltage (>0.9 V) and the power conversion efficiency reaches 2.47 %.