Bibridged bianchoring metal-free dyes based on phenoxazine and triphenyl amine as donors for dye-sensitized solar cell applications

The design and synthesis of two new metal-free bibridged bianchoring ambipolar dyes (D–(π–A)2) by linking electron-donating triphenyl amine or phenoxazine and electron-accepting cyanoacetic acid through a cyanovinyl thiophene π-bridge for fabrication of metal-free, dye-sensitized solar cells (DSSCs). The structures of the synthesized dyes were confirmed by NMR, mass spectrometry and elemental analysis. Experimental and theoretical (DFT) approaches revealed that the phenoxazine (POX-th-CN) dye exhibits a lower band gap (2.03 eV) compared to the triphenyl amine (TPA-th-CN) dye (2.19 eV). Due to this lower band gap, the electronic absorption of the phenoxazine dye becomes red-shifted, and, in addition, the fabricated dye-sensitized solar cell device based on this dye shows higher current conversion efficiencies (η = 1.78%) compared to the TPA-th-CN dye.