Synthesis and characterization of new fused benzimidazole quinazoline derivatives as photosensitizers for dye-sensitized solar cells

Despite advancements in DSSCs, photosensitizer efficiency remains a challenge. Traditional nitrogen-based compounds like benzimidazole-quinazoline derivatives show promise but face limitations in absorption and charge transfer. This study explores BIQ derivatives as innovative photosensitizers, leveraging enhanced photophysical properties through design, synthesis, characterization, and device fabrication to improve DSSC performance. Twenty (20) novel metal-free organic dyes, categorized into First Series (F1–F10) and Second Series (S1–S10), were designed using a Donor-π-Acceptor (D-π-A) architecture. The BIQ moiety was employed as the donor, phenyl-azomethine-(phenyl or thiophen-phenyl) as the π-spacer, and carboxyl or nitro groups as acceptors. Firstly, all BIQs were drawn using Avogadro 1.2.0 program. The ground state geometries of all the dyes are fully optimized using Gaussian09 program having B3LYP functional with standard 6-311G(d, p) basis set. The structural parameters and electronic properties, in particular the frontier molecular orbitals (FMOs) of the successfully optimized structures, were evaluated to conduct a more thorough examination. The computational results predicted a good charge separation from the donor unit (BIQ) to the acceptor unit as well as the values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) required for the operation of the DSSC, showing a good agreement with the values obtained by cyclic voltammetry (CV). In addition, the Second Series displayed a significant improvement in electronic, optical and photovoltaic properties due to the increase in bridge length. Secondly, Twenty BIQ-based compounds were synthesized in two series. The First Series (F1–F10) was obtained by condensing 2-(2- aminophenyl)-1H-benzimidazole [K2], derived from 1,2-diaminobenzene and o- nitrobenzaldehyde, with ten aromatic aldehydes. For the Second Series (S1–S10), compound F1 was oxidized and reduced to produce 4-(benzo[4,5]imidazo[1,2- c]quinazolin-6-yl)aniline [R2], which was then condensed with the same aldehydes to extend the π-bridge. Both series were thoroughly characterized using FTIR, NMR (1H and 13C), mass spectrometry, and elemental analysis, confirming their chemical structures. In order to evaluate the photophysical and electrochemical, ultraviolet– visible (UV-Vis) and cyclic voltammetry (CV) were carried out to obtain important information about the absorption and redox potential for BIQs. Among BIQs, S1, S8, and S10 displayed the smallest bandgaps at 2.40, 2.39 and 2.29 eV as well as broader absorption spectra at 475, 437 and 513 nm respectively. These properties allow the S1, S8, and S10 to absorb lower-energy photons from sunlight, thereby capturing a broader range of the solar spectrum leading to better light-harvesting efficiency. This increases the number of electrons excited to the conduction band, enhancing the photocurrent generation. as better candidates for DSSC device. Finally, the DSSC devices were fabricated using S1, S8, and S10. The results indicated that S10 that contained thiophene unit as extra π-spacer, exhibited higher power conversion efficiency (PCE) at 1.36% than S1 (0.62%) and S8 (0.73%). In addition, all compounds demonstrated high electron lifetime (τeff ) value, S1 (11.54), S8 (15.89), and S10 (22.14). In conclusion, BIQ-based dyes, particularly S1, S8 and S10, show promise as efficient, metal-free photosensitizers for next-generation DSSCs and exhibit improved electronic, optical and photovoltaic properties.

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