Studies on D-A-π-A structured porphyrin sensitizers with different additional electron-withdrawing unit

The introduction of an additional acceptor to a typical donor-π bridge-acceptor (D-π-A) type porphyrin sensitizer results in a D-A-π-A featured porphyrin. Two porphyrins containing an additional acceptor with different electron-withdrawing abilities such as 2,3-diphenylquinoxaline ( DPQ ) for LP-11 and 2,1,3-benzothiadiazole ( BTD ) for LP-12 between the porphyrin core and the anchoring group have been synthesized for use as sensitizers in dye-sensitized solar cells (DSCs). Compared to LP-11 , LP-12 with the stronger electron-withdrawing additional acceptor BTD possesses better light harvesting properties with regard to red-shifted Q-band absorption and a broader IPCE spectrum, resulting in a greater short circuit photocurrent density ( J sc ) output. Interestingly, the steric hindrance of the DPQ group is favorable for suppressing dye aggregation, leading to a larger open-circuit voltage ( V oc ) value for LP-11 -based cell. However, the loss in V oc of LP-12 is overcompensated by an improvement in J sc . The optimized cell based on LP-12 achieves the better performance with a J sc of 15.51 mA cm −2 , a V oc of 674 mV, a fill factor (FF) of 0.7 and an overall power conversion efficiency (PCE) of 7.37% under standard AM 1.5 G irradiation. The findings provide a guidance for the future molecular design of highly efficient porphyrin sensitizers for use in DSCs.