Efficient tuning of various coumarin based donor dyes with diketopyrrolopyrrole by forming D-A′-π-A structure for high-efficiency solar cells: A DFT/ TD-DFT study

Seven D-A '-pi-A structure of organic molecules with thiophene unit as pi-bridge linked with different donor groups of coumarin-based derivatives (D1-D7) and diketopyrrolopyrrole (DPP) as the auxiliary acceptor (A '), and cyanoacrylic acid as the acceptor (A), have been designed for potential application in dye sensitized solar cells (DSSCs). The effect of the electron donor unit and the auxiliary acceptor on the electronic, optical and photovoltaic properties have been evaluated for the dyes in isolated state and in chloroform solvent before and after binding to TiO2 cluster on the electron injection to the surface ability were investigated. Moreover, the D1-D7 dyes were evaluated and discussed using various parameters such as energy gap (E-gap), absorption spectra, light harvesting efficiency (LHE), open circuit voltage (V-OC), free injection energy (Delta G(inject)) and free regeneration energy (Delta G(reg)). The theoretical result show that all the designed dyes, in particular dyes D6 and D7, showed smaller E-gap, redshift absorption spectra, negative Delta G(inject) and fastest Delta G(reg) values compared to reference (R). Our results reveal that, all dyes provide excellent optoelectronic and photovoltaic properties. Especially D6 and D7 have potential for use as a sensitizer for DSSCs.