Advancing dye sensitized solar cell efficiency and computational insights into porphyrin based dyes

A comparative density functional theory (DFT) and time-dependent DFT (TD-DFT) study was conducted on twelve tetraphenylporphyrin sensitizers ( I–XII ), including five free-base/zinc complex pairs and two novel asymmetric dyes ( XI , XII ) modeled from the benchmark GY50 framework, to evaluate their potential for dye-sensitized solar cells (DSSCs). Electronic structures, vertical excitations, and spatial charge-transfer metrics ( \:qCT , \:dCT ) were evaluated at the CAM-B3LYP/LANL2DZ level using C-PCM solvation, while Multiwfn characterized wavefunction density differences. Interfacial chemisorption on anatase TiO 2 (101) was simulated using GGA/PBE-DNP on a \:(TiO₂)₃₆\: cluster model. For baseline dyes I–X , amino (-NH 2 ) donor substitution reduces the HOMO–LUMO gap (E g ) and alters orbital alignment. Target dyes XI and XII exhibit significantly narrowed HOMO–LUMO gaps \:(Eg=3.68-3.70\:eV in THF), intensified Q-band light-harvesting efficiency (LHE Q = 0.88), enhanced charge transfer \:qCT=0.47-0.480.17eme , \:dCT=3.10-3.17 A^∘ ), and remarkably low internal reorganization energies ( \:λ\:ᵢ=0.319-0.377 eV ), accelerating Marcus interfacial electron injection kinetics. Furthermore, dyes XI and XII demonstrate exothermic bidentate bridging chemisorption ( \:\:Eads=-15.21 to -16.71 kcal/mol ) with strong orbital coupling across the semiconductor interface. These findings establish a predictive computational framework for high-efficiency porphyrin photosensitizers.