Structural and Photophysical Studies of Triphenylamine-Based Organic Dyes for Applications in DSSCs: Experimental and DFT Analysis

In order to study the connection between structure of the molecular and sensitizing performance in dye-sensitized solar cells, four new organic sensitizers with donor-pi spacer-acceptor structures were designed and synthesized. The structural characterization of all dye sensitizers was investigated using FT-IR, ¹³C and ¹H NMR, CHN and UV–visible analyses. The electronic orbital transitions and optical properties were determined and discussed. (E)-2-cyano-3-(5-(3-(di-p-tolylamino)phenyl)furan-2-yl)acrylic acid (TPCA), (Z)-2-cyano-N′-((5-(3-(di-p-tolylamino)phenyl)furan-2-yl)acetohydrazide (TPCH), (E)-3-(5-(4-(bis(4-methoxyphenyl)amino)phenyl)furan-2-yl)-2-cyanoacrylic acid (MTPCA), and (Z)-N′-((5-(4-(bis(4-methoxyphenyl)amino)phenyl)furan-2-yl)methylene)-2-cyanoacetohydrazide exhibited band gaps (E_gap) in the range from 1.51 to 1.78 eV with λ_abs in the range of 486–589 nm. The dyes’ energy levels were investigated using the cyclic voltammetry technique and DFT calculations. To complement the comprehensive optical, electrochemical, and photovoltaic properties, density functional theory studies were conducted. Besides, important parameters such as open-circuit voltage, light harvesting efficiency, and band gap energy of the dye sensitizers were calculated and discussed. The theoretically calculated open-circuit voltage (V_oc) values ranged from 1.28 to 2.04 eV, while the light-harvesting efficiency (LHE) values varied from 0.11 to 0.22. Indeed, this theoretical research could guide chemists to synthesize effective dyes for DSSCs.