Optoelectronic Characterisation and Theoretical Insight into the Binding Mechanism of D-π-A Triphenylamine-Organic Dyes for Dye Sensitized Solar Cells

There has been a notable surge of interest in the field of dye sensitized solar cells (DSSCs) in recent years due to their remarkable performance in indoor/ambient and diffused light conditions. A significant portion of these highly efficient indoor DSSCs employs organic dyes based on triphenylamine. In this study, we present the findings of our investigation on two metal-free D-pi-A organic dyes, namely triphenylamine (YK 10) and hexyloxy-substituted triphenylamine (YK 11), serving as electron donors. These dyes feature a 3,3 ''-dioctyl-2,2 ':5 ',2 ''-terthiophene pi-spacer and cyanoacetic acid as the anchoring group. In order to comprehensively assess the relationship between the molecular structure, physical properties, and solar cell performance, we conducted in-depth analysis involving photophysical, electrochemical, and theoretical studies. Our results indicate that these dyes possess the ability to effectively capture light within the visible spectrum and exhibit suitable energetic characteristics for efficient electron injection and dye regeneration. Through the utilization of density functional theory (DFT) modeling, we explored the interfacial adsorption configuration of the dyes on the TiO2 semiconductor, revealing the involvement of the cyano group in the anchoring mechanism for both sensitizers. Moreover, the intramolecular S horizontal ellipsis CN interaction in these dyes was verified through topological quantum-theory-of-atom-in-molecule (QTAIM) analysis, which facilitates additional intramolecular charge transfer pathways. The DSSCs incorporating YK 10 and YK 11 demonstrated power conversion efficiencies (PCEs) of 6.42 % and 6.22 %, respectively, under full sun illumination (100 mW/cm2). Remarkably, under both standard 1000 lux CFL and LED illumination conditions, YK 11 exhibited superior performance with PCEs of 8.29 % and 5.89 %, respectively, surpassing the efficiencies of YK 10, which achieved 7.50 % and 5.09 % efficiencies under the same conditions. Detailed investigation of structure-property relationship contributing towards photovoltaic performance in D-pi-A triphenylamine-organic dye based dye-sensitized solar cells under outdoor and indoor illumination conditions.image