Advances in phenothiazine and phenoxazine-based electron donors for organic dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) as an elegant environmental solution for renewable energy production at a lower cost than conventional silicon solar cells have been of great interest, and this review is mainly concentrated on organic dye-sensitized solar cells. It is known that the dye chromophore is a heart component in the DSSC device. Two crucial characteristics in the dye design are the electron donor moiety and its geometry. Phenothiazine (PTZ) and phenoxazine (POZ) are electron donors with a butterfly-like geometry favouring a better dye design with less dye aggregation. On the other hand, skills in the synthesis of dyes suitable for DSSCs are needed. Therefore, this review focuses on the importance of choosing the right synthetic strategies to produce efficient dye chromophores using PTZ and POZ electron donors. The impact of the auxiliary donor, auxiliary acceptor, and the presence of di or multi anchoring groups in the dye molecule on its photovoltaic performance are discussed. In addition, the review presents the possibility of spectral coverage using a mixture of PTZ-based dyes with other dyes in terms of co-sensitization, the porphyrin-PTZ and POZ panchromatic dyes, the structural dependents HOMO-LUMO energies, the stability issue, and some granted patents in DSSCs using these electron donors.