Significant improvement of phenothiazine organic dye-sensitized solar cell performance using dithiafulvenyl unit as additional donor

The simple D-it-A phenothiazine organic dye (C(6)PTZ) was modified by introducing excellent electron donor dithiafulvenyl unit with alkyl chains as additional donor to form novel D-D-it-A organic dyes WD14 and WD15 for the first time. These organic dyes were successfully applied in dye-sensitized solar cells and the photovoltaic properties were investigated. Compared with the reference dye C6PTZ, the power conversion efficiencies increased significantly from 4.16% to 5.87% (WD14) and 6.63% (WD15). The performance improvement is due to the following advantages of the introduction of dithiafulvenyl unit with alkyl chains. Firstly, the light-harvesting capability is improved by increasing electron-donating ability. Secondly, it leads to more efficient inhibition of aggregation between dye molecules. Thirdly, the charge recombination between photoelectrons injected into the conduction band of TiO2 and the oxidized form (I-3(-)) of the redox couple is restricted due to the double blocking effect originating from the long hexyl chains of the dithiafulvenyl unit and hexyl side chain attached to phenothiazine unit. This work indicates that the incorporation of dithiafulvenyl unit into the simple phenothiazine organic dye greatly improves the solar cell performance, and it will be an effective approach to develop high-performance metal-free organic dyes. (C) 2015 Elsevier B.V. All rights reserved.