A theoretical interpretation and screening of porphyrin sensitizer candidates with anticipated good photo-to-electric conversion performances for dye-sensitized solar cells

Tetraphenylporphyrin zinc complex (ZnTPP) as donor and nine acceptors A-I, which have different combinations of lengths, components of the linkers, and functional groups adjacent to the carboxyl acid group, were designed and calculated at density functional B3LYP level. The molecular orbital energy levels of ZnTPP donor and the acceptors were compared to screen promising combinations to form the sensitizer candidates with anticipated good photo-to-electric conversion performances. Several zinc metalloporphyrins screened were then constructed and studied by DFT/TDDFT calculations. As compared with the experimental results of some porphyrin sensitizers used in dye-sensitized solar cells previously, the molecules with a relatively longer conjugative linker and a strong electron-withdrawing group such as CN adjacent to the carboxyl acid group seem to provide higher photo-to-electric conversion efficiencies. The novel dyes, 2-cyano-3-[4′-(2″-(5″,10″,15″,20″-tetraphenylporphyrinato zinc(II))yl)-phenyl]-acrylic acid (ZnTPPG) and 2-alkynyl-3-[4′-(trans-2″-(2″′-(5″′,10″′,15″′,20″′-tetraphenylporphyrinato zinc(II))yl) ethen-1″-yl)-phenyl]-acrylic acid (ZnTPPI) designed in the current work were found promising to provide good photo-to-electric conversion performance. With further optimization of the manufacturing process, better performances for 2-cyano-5-(2′-(5′,10′,15′,20′-tetraphenylporphyrinato zinc(II))yl)-penta-2,4-dienoic acid (ZnTPPC) and 2-cyano-3-[4′-(trans-2″-(2″′-(5″′,10″′,15″′,20″′-tetraphenylporphyrinato zinc(II)yl) ethen-1″-yl)-phenyl]-acrylic acid (ZnTPPH) may also be obtained.