A structurally simple donor with a low recombination rate for high-performance dye-sensitized solar cells

Abstract

Two dyes with dithieno[3,2-b:20,30-d] pyrrole (DTP) as the donor (An101 and An102) have been synthesized and characterized. An101 and An102 were applied to dye-sensitized solar cells (DSSCs) and power conversion efficiencies (PCEs) of 8.0% and 9.5% were achieved with the I2−/I3− redox couple, which correspond to open voltages (Voc) of 784 and 690 mV, current densities (Jsc) of 15.1 and 20.0 mA cm−2, the fill factors of 67.2% and 68.7%, respectively, under AM1.5G irradiation. It is worth noting that the different connection locations of the donors with the π-bridge result in different PCEs. An102 has a higher Jsc owing to its high molar extinction coefficient and small torsion angle, which increase the light-harvesting ability and coplanarity. An101 has a higher Voc owing to introduction of the alkoxybenzene group, which can effectively suppress recombination with the electrolyte and dye. By scanning with different bias voltages with electrochemical impedance spectroscopy, the reason for the high voltage of the An101 dye is up-shift of the TiO2 conduction-band edge and elongated electron lifetimes. However, the main reason for the relatively high PCE of the An102 dye is the coplanarity, which results in good long-term stability.