First-principles study of efficient phenothiazine-based D-π-A organic sensitizers with various spacers for DSSCs

Design of highly efficient sensitizers is one of the most significant issues for dye-sensitized solar cells (DSSCs). In this work, we designed and screened a series of phenothiazine-derivative dyes with donor-pi spacer-acceptor (D-pi-A) architecture based on a structural configuration with a phenothiazine group as the donor (D) part, a thiophene as the linker (pi), and a 2-cyanoacrylic acid moiety (A) as the electron-acceptor segment, comparing the effects of different pi-spacer groups between the electron donor and acceptor. The effects of different electron-deficient linker units on the absorption/emission spectra and photovoltaic properties were investigated by a combination of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. Based on the ground-and excited-state geometries, the absorption and emission spectra were calculated using the TD-DFT method. Different exchange-correlation functionals were first applied to establish a proper methodology for calculating the excited-state energy of the reference dye, known as TC104. The theoretical results calculated using the TD-CAM-B3LYP/B3LYP method with 6-311++G(d,p)/6-31G(d,p) basis set were found to agree well with the absorption and emission wavelengths for TC104 found experimentally. Overall, dye molecules SP1-SP4 (especially SP2 and SP4) were found to be promising sensitizers for highly efficient organic DSSCs. [GRAPHICS] .