D-π-A structured porphyrin sensitizers for dye-sensitized solar cells

Two porphyrin-based D-pi-A structured dyes of SGT-026 and SGT-027 with different acceptor groups were synthesized and characterized for dye-sensitized solar cells. The structure of SGT-027was designed with a very strong acceptor unit of (5-(naphtho[1,2-c:5,6-c]bis[1,2,5]-thiadiazolyl)benzoic acid) (NBTD), resulting in more red-shifted absorption bands and broader NIR absorption ability, but SGT-026 porphyrin with a weak acceptor unit of (2-(thieno[3,4-c]pyrrole-4,6(5H)-dionyl)benzoic acid) (TPD) exhibited a blue-shifted Q band absorption, compared to the reference SGT-021dye with a strong acceptor unit of (4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid) (BTD). The photophysical properties of these D-pi-A structured porphyrin sensitizers depend on the degree of the intramolecular charge transfer character with the electron-withdrawing ability order of NBTD > BTD > TPD. The photovoltaic performances were evaluated using cobalt (II/III)-based redox electrolyte, SGT-027 reached a power conversion efficiency (PCE) of up to 7.5%, which was surprisingly inferior to the benchmark porphyrin sensitizer SGT-021 with a PCE of 10.9%, and a PCE of 5.9% was exhibited by SGT-026, under AM 1.5G sunlight. The optical, and electrochemical properties and DFT calculations were utilized to understand the cell performance difference between SGT-dyes.