Molecular engineering of D-A-π-A sensitizers for highly efficient solid-state dye-sensitized solar cells

Two newquinoxaline-based D-A-pi-A organic sensitizers AQ309 and AQ310 have been designed and synthesized employing 3,4-ethylenedioxythiophene (EDOT) and cyclopentadithiophene (CPDT) as plinker units, respectively. The new AQ309 and AQ310 dyes have been applied in all-solid-state dye-sensitized solar cells (ssDSSCs). An impressive record photoelectric conversion efficiency (PCE) of 8.0% for AQ310-based ssDSSCs using Spiro-OMeTAD as the hole transport material (HTM) was obtained under standard AM 1.5 (100 mW cm (2)) solar intensity. This clearly outperforms the PCE of the state-of-theart organic D-pi-A dye LEG4-based devices showing a PCE of 7.3% under the same conditions. Moreover, an excellent high PCE of 8.6% was also recorded for AQ310-based devices under 50% solar intensity. Meanwhile, the AQ310-based ssDSSCs showed a much longer electron lifetime according to the transient photovoltage decay measurement, demonstrating lower charge recombination losses in the devices. Photo-induced absorption spectroscopy (PIA) indicated that AQ310 could be more efficiently regenerated by Spiro-OMeTAD. These results show that molecular engineering is a promising strategy to develop D-A-pi-A organic sensitizers for highly efficient ssDSSCs.