Computational Insight into the Optoelectronic and Chemical Reactivity Properties of Metal-Free Phenothiazine Based D-π-A Dye-Sensitizers for Solar Cells Application: DFT and TD-DFT Methods

The molecular and electronic tuneability of organic dye-sensitizers coupled with low cost compared to Silicon-Germanium solar cells have made dye-sensitized solar cells prominent alternative renewable source of energy to meet the growing in energy demand to power the economic, industrial and technological development of the world. Nevertheless, considerable improvement in power to energy conversion is still needed, thus design various tuneable dyes are still ongoing in this direction. In this work, eight organic dyes consisting of four 2-[3-(10H-phenothiazin-3-yl)furan-2-yl]-10H-phenothiazine based (PZ) and four 2-[3-(10H-phenoxazin-3-yl)furan-2-yl]-10H-phenoxazine based (PO) in form of D-pi-A architecture were computationally designed and studied for possible utilization as dye-sensitizers in dye-sensitized solar cells (DSSCs). DFT/TD-DFT (B3LYP/6-31G**) method was to calculate and evaluate the effects of geometry, frontier orbital energies and optoelectronic properties on performance characteristics of the dyes. The results showed that PZ dyes have longer absorption lambda max than corresponding PO series, which in agreement with reorganization energy (lambda total\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\lambda }_{total}$$\end{document}). Chemical reactivity descriptors showed that electrophilicity (omega) and electron accepting power (omega+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }<^>{+}$$\end{document}) and electron donating power (omega-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }<^>{-}$$\end{document}) of the dyes favoured PZ-1, PO-1 and PZ-3 dyes. All the dyes would have good injection drive force (Delta Ginject\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta G}<^>{inject}$$\end{document}), but only PO-2 and PO-1 would have considerably larger driving force for regeneration. The exciting lifetime (tau) revealed that PZ-1 (27.42 ns), PO-1 (17.14 ns), PZ-3 (16.17 ns) and PO-3 (13.45 ns) would delay in charge recombination, which could increase the DSSCs' efficiency.