Three benzo[a]phenoxazine based photosensitizers known as 10-Chloro-6-methyl-5H benzo[α]phenoxazin-5-one (BPO-Cl), 6-methyl-5H-benzo[α]phenoxazin-5-one (BPO), and 6-methyl-5H-benzo[α]phenothiazin-5-one (BPT) synthesized from provitamin K3 were used as photosensitizers to fabricate a DSSC device. The inbuilt intra-molecular charge transfer (ICT), favorable π–π interaction, planar shape, and compatible redox nature with appropriate frontier molecular orbitals (HOMO and LUMO) alignment are the significant physicochemical characteristics of benzo[α]phenoxazine moiety that rationalize to become an efficient photosensitizer. Thus, the bare benzo[a]phenoxazine dyes without any efficient anchor and donor group are evaluated here with their intrinsic chemical behavior for efficient precursors in various energy transferring material. The intramolecular charge transfer occurring through aromatic rings bridged by two heteroatoms (O/S and N) is tunable with DFT analysis and single-crystal XRD data. The characteristic solar cell parameters show that chlorine substitution enhances the open-circuit voltage (Voc) from 0.53 V in BPO to 0.56 V in BPO-Cl. A noticeable enhancement in short-circuit current density (Jsc) nearly fivefold is observed for BPO dye compared to its thio-substituted BPT unit. The substitution of chlorine reduces the recombination rate in the device studied from electrochemical impedance spectroscopy. Thus BPO template is an excellent precursor to tailor various D/A groups to produce effective photosensitizer evaluated by physicochemical properties tunable with several optoelectrical, structural, morphological, and electrochemical analyses.