Five cost-effective porphyrin based sensitizers with various donor groups (bisthiophene, N,N-dimethylaminophenyl, triphenylamine, carbazole and phenothiazine) and meso-dimesityl as auxiliary groups have been synthesized through the shortest possible synthetic route for the practical commercialization of these dyes. trans-A2BC porphyrin dyes show power conversion efficiencies (η) ranging from 5.3% to 7.11% under 1 sun illumination and highly depend on donor strength of appended moiety. Our molecular design incorporates trans-10,20-dimesityl groups, which prevents the π–π aggregation between the porphyrin units onto the TiO2 surface. The porphyrin dye (RA-200-Zn) bearing phenothiazine as donor unveils the highest photon-to-current conversion efficiency (PCE) of 7.1% and showed butterfly conformation, which can restrict the intermolecular aggregation. Further, this dye shows a broader absorption on TiO2 surface and significantly increased IPCE values in visible region as compared to the other dyes, which assured better light harvesting ability with high short-circuit current density (J sc) of 14.2 mA cm–2.

Organic dyes possessing conjugated π-framework forms closely packed monolayers on photoanode in dye-sensitized solar cell (DSSC), because of the limitation to control the orientation and the extend of intermolecular π-π interaction, self-aggregation of dyes leads to reduced cell performance. In this report, a series of homodimeric (D-D and D-D) and heterodimeric (D-D and D-D) donor/acceptor (D/A) dyes containing spiroBiProDOT π-spacer were designed and synthesized by utilizing Pd-catalyzed direct arylation reaction and correlates the device performance with monomeric dyes (D and D). Both the thiophenes (π-spacer) of spiroBiProDOT were functionalized with same or different donor groups which led to homodimeric and heterodimeric chromophores in a single sensitizer. The homodimeric spiro-dye D-D showed higher power conversion efficiency (PCE), of 7.6% with a V and J of 0.672 V and 16.16 mA/cm, respectively. On the other hand, the monomeric D exhibited a PCE of 3.2% (V of 0.64 V and J of 7.2 mA/cm), which is lower by 2.4 fold compared to dimeric analogue. The spiro-unit provides flexibility between the incorporated chromophores to orient on TiO due to four sp-centers, which arrest the molecular motions after chemisorption. This study shows a new molecular approach to incorporate two chromophores in the dimeric dye possessing complementary absorption characteristics toward panchromatic absorption. The attenuated charge recombination at TiO/Dye/redox couple interface in case of D-D, owing to better passivation of TiO surface, was elucidated through impedance analysis. The FT-IR spectrum of D-D adsorbed on TiO film indicated both the carboxylic units were involved in chemisorption which makes strong coupling between dye and TiO.

Zn(ii) porphyrin dyes have been synthesized in three steps and exhibited power conversion efficiencies of 2.1 to 4.2% which depend on the electron donating ability of the R group.

A series of four unsymmetrical squaraine dyes, XSQ1-4, were synthesized using a fused fluorenylindolenine-based donor unit for dye-sensitized solar cells (DSSCs). The fused structure of fluorenylindolenine helped in moving the absorption toward the near-infrared (NIR) region, and the two sp-C centers available on this donor were utilized to incorporate out-of-plane alkyl chains in opposite directions to control the dye-dye interactions on the TiO surface. High extinction coefficient (ε ≥ 10 M cm) for absorbing NIR photons and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels with respect to the conduction band of TiO and electrolyte for charge injection and dye regeneration processes, respectively, make these dyes potential sensitizers for DSSCs. Introduction of branched alkyl groups in the π-framework helped in controlling dye aggregation to reduce exciton quenching and assisted in TiO surface passivation to avoid the charge recombination process. Furthermore, having a naphthyl group on the indole part of the anchoring group containing segment helped to red-shift the absorption spectrum of dyes 15 nm toward the NIR region (XSQ3-4). Among all of the dyes under investigation, XSQ2 gave the best photovoltaic performance, having a short-circuit current density ( J) of 13.99 mA cm, open-circuit voltage ( V) of 0.66 V, and a fill factor (ff) of 0.71, with a device performance (η) of 6.57%. Electrochemical impedance spectroscopy revealed higher electron lifetime on TiO for XSQ2, which helps to avoid the charge recombination process.