We describe the synthesis and preliminary photovoltaic performance of a solution-processable organic small-molecule electron donor DT-DPP(TVT)2 that consists of dithienyldiketopyrrolopyrrole (DT-DPP) as the core and thienylvinylthiophene (TVT) as the endgroups. The new compound is a crystalline solid with a Tm of approximately 216°C. Cyclic voltammetry indicates that DT-DPP(TVT)2 exhibits two quasi-reversible one-electron oxidation waves at ca. 0.68 and 0.90 V versus an Ag/AgCl reference electrode, respectively, leading to an estimated highest occupied molecular orbital (HOMO) level of about −5.08 eV. Introducing the branched 2-hexyldecyl side chain provides DT-DPP(TVT)2 with a high solubility in chloroform up to ca. 36 mg mL−1 at room temperature. Thermal annealing increases the crystallinity of the as-cast film from chloroform solution, thereby rendering slightly red-shifted charge-transfer absorption maxima. Fitting the space-charge-limited current characteristics of the thermally annealed thin film yields an improved hole mobility of ∼2.14×10−4 cm2 V−1 s−1 at low voltages versus ∼1.46×10−4 cm2 V−1 s−1 of the as-cast film. A first characterization of the solar cell [ITO/PEDOT: PSS/DT-DPP(TVT)2: PC61BM/Al] produces a power conversion efficiency of ∼3% with VOC≈0.78 V, JSC≈7.91 mA cm−2, and FF≈48.7%, under simulated AM1.5G with an illumination intensity of 100 mW cm−2. It should be noted that the thermal effect on the thin film absorption of DT-DPP(TVT)2 does not seem to be completely similar to the molecular donor DPP(TFNa)2 reported earlier, which bears 6-fluoronaphthyl endgroups.
The synthesis of new small-molecule amine compounds is presented. The triamino derivative with ethyl substituents
possesses better processability in alcoholic solvent and was utilized as an electron-injection layer in organic light-emitting diodes (OLEDs) in order to avoid interlayer mixing. The performance of the resulting OLEDs that consisted of
an Al cathode and a solution-processed molecular green-emitting layer is shown to depend on the thickness of the small-molecule electron-injection interlayer and is preliminarily discussed.