Improved solubility of asymmetric tetraethynylporphyrin derivatives for solution-processed organic solar cells

Abstract Asymmetric magnesium tetraethynylporphyrin derivatives bearing two diketopyrrolopyrrole (DPP) units and two different aryl units were synthesized by multistage Sonogashira coupling reactions. According to saturated UV–Vis–NIR spectra, the solubility of the asymmetric porphyrin derivatives was superior to that of symmetric porphyrin derivatives. Frontier orbital energies were investigated in the solution state by differential pulse voltammetry and in the solid state by photoelectron yield spectroscopy and UV–Vis–NIR spectroscopy. Time-dependent density functional theory calculations were carried out to simulate the UV–Vis–NIR absorption spectra and revealed splitting of the Q band into two bands at 712 nm and 650 nm. The thickness of active layers in solution-processed organic solar cells was influenced by the solubility of the porphyrin derivatives. When the compound with the highest solubility was used ( 2d ), the film thickness was 215 nm, which is larger than-the thickness of ∼120 nm reported for symmetric porphyrin derivatives. Also, the short-circuit current density (J SC ) was influenced by solubility, especially for compound 2d , compared with other asymmetric compounds 2a–c . The optimized device conditions using 2d and PC 61 BM gave J SC of 14.86 mA/cm 2 , open-circuit voltage of 0.69 V, fill factor of 0.47, and power conversion efficiency of 4.84%.