Cosensitization of a Tetraethylene Glycol-Substituted Unsymmetrical Zinc Phthalocyanine Sensitized Solar Cells with D131 Auxiliary Dye Exhibited Enhanced Efficiency

Abstract

An asymmetric zinc phthalocyanine dye (ZnPcT₃C), bearing three tetraethylene glycol donor groups and one carboxylic acid anchoring group, was synthesized as a photosensitizer dye for dye-sensitized solar cells (DSSCs). The tetraethylene glycol (TEG), consisting of four ethoxy units, works as an amphiphilic long-chain donor group that greatly helped in reducing the molecular aggregation. Carboxylic acid group, on the other hand, an acceptor, together with TEG in ZnPcT₃C functions as a ‘push–pullʼ system suitable for DSSCs. Absorption spectra of ZnPcT₃C in DMSO showed a strong sharp Q band in the infrared region 600–700 nm with (λ_max = 682 nm) and a less intense soret band appeared in the region 300–400 nm with λ_max = 340 nm. The zinc phthalocyanine (ZnPcT₃C) exhibited molar extinction coefficient (ε) of 72,727 L mol⁻¹cm⁻¹. The emission was observed at λ_em = 695 nm upon excitation at 650 nm and exhibited a fluorescence decay of 2.82 ns. The ZnPcT₃C dye sensitised solar cell (c = 1 mM) exhibited the power conversion efficiency (η) of 3.52% in chloroform in I⁻/I₃ electrolyte under simulated 100% brightness. Cosensitization of ZnPcT₃C with another auxiliary dye D131 in 1:1 ratio in a cocktail-type DSSC attained the power conversion efficiency of twice as high as η = 6.27% in an identical condition. A mixture of D131 (λ_max = 470 nm) dye with the ZnPcT₃C phthalocyanine harvests sunlight across the visible spectra, enabling DSSCs to attain a large photocurrent and photovoltage, enhancing power conversion efficiency.