Highly efficient novel unsymmetrical Zn and TiO naphthalenephthalocyanine and YD2 porphyrin dyes as co-sensitizers for DSSCs

Novel unsymmetrical zinc and oxotitanium phthalocyanine (NPcs) dyes containing 4-tert-butylsulfanyl group and carboxylic acid anchor group (ZnNSPPc and TiONSPPc) were synthesized and employed as sensitizing agents for dye-sensitized solar cells (DSSCs). Synthesized NPc dyes were characterized by FTIR, UV–Vis, ¹H and ¹³C NMR techniques. Also, density functional theory (DFT) studies were utilized to investigate molecular structures and electronic parameters such as the highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) values. The DSSCs were characterized with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Furthermore, cocktails of synthesized NPc dyes with YD2 porphyrin at different ratios were prepared to acquire high-efficiency solar cells. DSSCs that were sensitized with only ZnNSPPc and TiONSPPc have photon conversion efficiency (PCE) values of 5.59 % and 6.23 %, respectively. For DSSCs sensitized with cocktail dyes, the highest efficiency belongs to the YD2-ZnNSPPc mixture (3:1), with a value of 11.64 % due to the panchromatic effect.