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Abstract Four novel dyes featuring new semi-rigid triphenylamine donor groups have been synthesized and successfully employed as sensitizers in dye-sensitized solar cells (DSSCs). Opting for the new semi-rigid triphenylamine (tPA) electron-donating unit yielded a better V oc and J sc resulting to a power conversion efficiency (PCE) which is 16% higher compared to a reference dye whose electron-donating group is a conventional tPA unit. Density functional theory (DFT) and time-dependent DFT calculations revealed the more favorable charge-transport properties of the dye based on the new semi-rigid donor unit. Among the synthesized dyes, the DSSC device based on Dhkx-4 dye in conjunction with iodine-based electrolyte achieved a PCE of 6.23%, with V oc of 0.661 V, J sc of 13.31 mAcm−2, and FF of 0.71 under simulated AM 1.5 G condition. Therefore, the novel semi-rigid tPA donor unit presented in this work is a promising donor group for a sensitizer in DSSCs and systematic structural engineering of the presented designs could offer valuable contributions for the development of the photovoltaic devices. Graphical abstract Image 1 Highlights • D-π-A dyes based on a new semi-rigid triphenylamine donor were synthesized for DSSCs. • The new Dhkx-1 dye attained a PCE that is 16% higher than the L1 reference dye. • The experimental data are interpreted well by the results of DFT/TD-DFT calculation. • The solar cell device based on a simple Dhkx-4 dye attained the highest PCE of 6.23%. [ABSTRACT FROM AUTHOR]

The use of theoretical techniques in the structural development of dye-sensitized solar cells helps in the efficient screening of the dyes. To properly rationalize the dye’s design process, benchmark calculations were conducted using long-range corrected exchange–correlation (xc) functionals with varying separation parameters to be able to predict the excited-state energies of triphenylamine-based dyes, namely: PPS, PSP, and PSS, wherein they differ at the π-conjugated bridge using thiophene and/or phenyl moieties. The results show that LC- ω PBE xc functional with an optimized parameter provided better correlation with the experimental results compared to the other functionals. The relative shifts of the absorption spectra, light harvesting efficiency, normal dipole moments, as well as the ionization potentials and electron affinities of the dyes were well-correlated with the experimental data. A new set of dyes was designed in an effort to increase its solar cell efficiency that was patterned after PSS with an additional donor moiety such as fluorene, cyclopentaindole, and pyrene attached asymmetrically at the triphenylamine ring. Among the newly designed dyes, analogs that contain 4-phenyl-1,2,3,4-tetrahydrocyclopenta[ b ]indole (I) and pyrido[2,3,4-5- imn ]phenanthridine-5,10(4 H ,9 H )-dione (P2) as the additional donor moiety produced the best photophysical properties and charge-transfer characteristics for a promising dye for solar cell applications. [ABSTRACT FROM AUTHOR]