Design and theoretical study of phenothiazine-based low bandgap dye derivatives as sensitizers in molecular photovoltaics

Modulation of metal free organic (MFO) molecules become imperative to researchers to obtain low-cost sensitizer for dye sensitized solar cells (DSSCs) purposes. A series of metal free phenothiazine-based (PTZ) organic dyes are designed and optimized as sensitizers for DSSCs application. Their electronic and optical properties were probed using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) approaches. Effects of additional donor unit, pi -conjugation bridges, and benzothiadiazole (BTDA) were investigated. Introducing BTDA in the acceptor unit leads to the tailoring of the energy band gap and promotion of charge transfer within donor and anchor groups with increased effective parameters in DSSC efficiency. The addition of diphenylamine, triphenylamine, or hexyloxyphenyl to the PTZ unit increased electron delocalization and enhanced intramolecular charge transfer. Changing pi -spacer from phenyl to thiophene has a great effect on the electronic properties and absorption spectra of the dyes. The relationship between light harvesting efficiency (LHE) and chemical hardness (?) shows that structural design that consists of BTDA and thiophene as pi -spacer tends most towards excellent performance as dye sensitizers in DSSCs.