Bithiazole-bridged dyes for dye-sensitized solar cells with high open circuit voltage performance

Abstract

Five new metal-free organic dyes (T1–T5) containing bithiazole moieties were synthesized and used for dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical and photovoltaic properties were fully characterized. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the donor moiety. All of these dyes performed as sensitizers for the DSSC test, and the photovoltaic performance data of these bithiazole-bridged dyes showed higher open circuit voltages (745–810 mV). Among the five dyes, T1 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 83.8%, a short-circuit photocurrent density (J_sc) of 11.78 mA cm⁻², an open-circuit photovoltage (V_oc) of 810 mV, and a fill factor (ff) of 0.60, corresponding to an overall conversion efficiency of 5.73% under standard global AM 1.5 solar light condition, which reached 93% with respect to that of an N719-based device fabricated under similar conditions. The result shows that the metal-free dyes based on bithiazole π-conjugation are promising candidates for improvement of the performance of DSSCs.