New sensitizers bearing quinoxaline moieties as an auxiliary acceptor for dye-sensitized solar cells

Two organic sensitizers (LI-40 and LI-41) containing 6,7-bis(hexyloxy)-2,3-dimethylquinoxaline unit and thiophene or furan as conjugated bridge were synthesized and utilized for dye-sensitized solar cells (DSSCs). The incorporation of quinoxaline unit brought about impressive changes in absorption spectra and energy levels, thus, enhanced the light-harvesting for photovoltaic conversion and facilitated the electron transfer, resulting in a great improvement in the electron distribution of the whole molecule. The solar cell based on LI-40 exhibited a broad incident photon-to-current conversion efficiency (IPCE) spectrum and high conversion efficiency (η = 6.75%). While under the same measuring conditions, the reference sensitizer PSS, which had similar structure to LI-40 but without the quinoxaline unit in the conjugated bridge, only gave the η value of 4.50%, indicating that the sensitizers are promising candidates to improve the performance of DSSCs.