Two new heteroleptic ruthenium complexes, coded as KW1 and KW2, featuring triphenylamine electron-donating antennas, have been synthesized and used in dye-sensitized solar cells (DSSCs). Compared to the reference dye Z907, these new dyes exhibit broad absorption and efficient light harvesting properties. Particularly the KW2 dye exhibits a low-energy metal–ligand charge transfer band centred at 554 nm with a high molar extinction coefficient of 2.43 × 104 M−1 cm−1 arising from an extended conjugation in the donor antenna ligand. Photovoltaic devices using these sensitizers in conjunction with a volatile electrolyte show high photovoltaic conversion efficiencies of ∼10.7% under full sunlight irradiation (AM 1.5G, 100 mW cm−2). This efficiency is nearly 20% higher than that of the Z907-based reference device, which is attributed to a largely improved short circuit current. The distinct effects of different donor antennas incorporated in the ancillary ligands on the primary photovoltaic parameters in these devices are investigated with transient photoelectrical decays and impedance spectroscopy measurements. The devices utilizing these highly efficient light harvesting ruthenium sensitizers featuring triphenylamine donor antennas in combination with low volatility electrolytes exhibit good durability during the accelerated tests (60 °C for 1000 h in a solar simulator, 100 mW cm−2).

With a view to broadening the porphyrin light-harvesting cross section and improving mesoporous solar cell power conversion efficiency, pyrene-conjugated porphyrin dyes with various π-spacers between the porphyrin chromophore and carboxylic acid have been designed and synthesized in this study, including tailoring with phenyl (LW17), thiophene (LW18), and 2-phenylthiophene (LW19). These porphyrins show stepwise red-shifted absorption spectra and consistently decreased oxidation potential when the spacer changes from phenyl to an electron-rich unit of thiophene, and to an elongated spacer of 2-phenylthiophene, respectively, for LW17, LW18, and LW19 dyes. A mesoporous solar cell based on LW18 dye can achieve an overall power conversion efficiency of 8.7% under full sunlight (AM 1.5G, 100 mW cm−2) irradiation. The result reveals that both photocurrent and photovoltage can be effectively tuned by changing the spacers. Detailed investigation with transient photovoltage decay measurements provides general information on factors affecting the principal photovoltaic parameters.

This work introduces cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) as a spacer between the porphyrin chromophore and cyanoacetic acid to obtain a porphyrin dye (coded as LW9). The resultant novel porphyrin dye exhibits extended absorption spectra and a split B band at 520 nm. Therefore, a full spectrum light harvesting characterization of sensitized TiO2 mesoporous film can be achieved. To conduct a thorough investigation of the influence of the spacer unit, new sensitizers conjugated with biphenyl (LW7) and bithiophene (LW8) have been synthesized. As the electron-donating ability of the spacer varies from biphenyl to bithiophene and cyclopenta[1,2-b:5,4-b′]dithiophene, stepwise red-shifted electronic absorption spectra and the consistently decreasing energy gap of the dye are presented. These novel porphyrins have been evaluated in dye-sensitized solar cells, achieving a power efficiency of 6.5% employing a [Co(bpy)3]2+/3+ redox couple for the LW9 device under reporting conditions. Detailed investigation, including time-resolved photoluminescence, transient photovoltage decay, and scanning electrochemical spectroscopy measurements, provides important information on the factors affecting the principal photovoltaic parameters. The present report highlights the potential of D–π–D–A porphyrin for the development of efficient sensitizers with broad light absorption properties.

Recently, p-type dye-sensitized solar cells (p-DSSCs) have attracted increasing attention. The widely used carboxylic acid groups for TiO2 based sensitizers may not be the optimal choice for p-DSSCs. Herein new donor-π-acceptor organic sensitizers with pyridine ring as anchoring group are designed and synthesized for p-DSSCs. The detailed investigation demonstrates that carboxylic acid groups may have an effect on the negative shift of the valence band edge of NiO induced by surface protonation, which lowers the hole-injection process and the device photovoltage, while the pyridine ring works effectively without this problem. The p-DSSC based on the new sensitizer shows an overall conversion efficiency of ∼0.16% under full sunlight (AM 1.5G, 100 mW cm–2) irradiation.

Two new D−π–A porphyrin sensitizers (coded as LW5 and LW6) with extended conjugation units at π moiety are designed and synthesized for mesoscopic solar cells. While keeping the same donor moiety to the well-investigated porphyrin LD14, introduction of various linker units in the two new sensitizers with electron rich property can red-shift the absorption spectra to 710 nm, such as thiophene for the LW5 dye between porphyrin macrocycle and 4-ethynylbenzoic acid (i.e., the acceptor). The excited singlet state lifetime and charge regeneration rate constants have been examined to be ∼140 ps and 1 × 10–3 cm s–1 with time-resolved photoluminescence and scanning electrochemical microscopy measurements, respectively, indicating fast electron injection from the excited dyes to the TiO2 conduction band followed by quick charge regeneration of dye cations by electrolytes containing a [Co(bpy)3]2+/3+ redox couple. LW5 and LW6 dyes have been evaluated in dye-sensitized solar cells, showing efficiencies of 7.8% and 6.1% with [Co(bpy)3]2+/3+ based electrolytes (measured under standard test conditions), respectively. A detailed investigation with transient photovoltage decay measurement provides important information on factors affecting the principal photovoltaic parameters.

Two new heteroleptic ruthenium complexes, coded as KW1 and KW2, featuring triphenylamine electron-donating antennas, have been synthesized and used in dye-sensitized solar cells (DSSCs). Compared to the reference dye Z907, these new dyes exhibit broad absorption and efficient light harvesting properties. Particularly the KW2 dye exhibits a low-energy metal–ligand charge transfer band centred at 554 nm with a high molar extinction coefficient of 2.43 × 104 M−1 cm−1 arising from an extended conjugation in the donor antenna ligand. Photovoltaic devices using these sensitizers in conjunction with a volatile electrolyte show high photovoltaic conversion efficiencies of ∼10.7% under full sunlight irradiation (AM 1.5G, 100 mW cm−2). This efficiency is nearly 20% higher than that of the Z907-based reference device, which is attributed to a largely improved short circuit current. The distinct effects of different donor antennas incorporated in the ancillary ligands on the primary photovoltaic parameters in these devices are investigated with transient photoelectrical decays and impedance spectroscopy measurements. The devices utilizing these highly efficient light harvesting ruthenium sensitizers featuring triphenylamine donor antennas in combination with low volatility electrolytes exhibit good durability during the accelerated tests (60 °C for 1000 h in a solar simulator, 100 mW cm−2).

This work introduces cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) as a spacer between the porphyrin chromophore and cyanoacetic acid to obtain a porphyrin dye (coded as LW9). The resultant novel porphyrin dye exhibits extended absorption spectra and a split B band at 520 nm. Therefore, a full spectrum light harvesting characterization of sensitized TiO2 mesoporous film can be achieved. To conduct a thorough investigation of the influence of the spacer unit, new sensitizers conjugated with biphenyl (LW7) and bithiophene (LW8) have been synthesized. As the electron-donating ability of the spacer varies from biphenyl to bithiophene and cyclopenta[1,2-b:5,4-b′]dithiophene, stepwise red-shifted electronic absorption spectra and the consistently decreasing energy gap of the dye are presented. These novel porphyrins have been evaluated in dye-sensitized solar cells, achieving a power efficiency of 6.5% employing a [Co(bpy)3]2+/3+ redox couple for the LW9 device under reporting conditions. Detailed investigation, including time-resolved photoluminescence, transient photovoltage decay, and scanning electrochemical spectroscopy measurements, provides important information on the factors affecting the principal photovoltaic parameters. The present report highlights the potential of D–π–D–A porphyrin for the development of efficient sensitizers with broad light absorption properties.

With a view to broadening the porphyrin light-harvesting cross section and improving mesoporous solar cell power conversion efficiency, pyrene-conjugated porphyrin dyes with various π-spacers between the porphyrin chromophore and carboxylic acid have been designed and synthesized in this study, including tailoring with phenyl (LW17), thiophene (LW18), and 2-phenylthiophene (LW19). These porphyrins show stepwise red-shifted absorption spectra and consistently decreased oxidation potential when the spacer changes from phenyl to an electron-rich unit of thiophene, and to an elongated spacer of 2-phenylthiophene, respectively, for LW17, LW18, and LW19 dyes. A mesoporous solar cell based on LW18 dye can achieve an overall power conversion efficiency of 8.7% under full sunlight (AM 1.5G, 100 mW cm−2) irradiation. The result reveals that both photocurrent and photovoltage can be effectively tuned by changing the spacers. Detailed investigation with transient photovoltage decay measurements provides general information on factors affecting the principal photovoltaic parameters.