Effects of Immersion Solvent on Photovoltaic and Photophysical Properties of Porphyrin-Sensitized Solar Cells

Antenna Effect in Noble Metal-Free Dye-Sensitized Photocatalytic Systems Enhances CO2 -to-CO Conversion

Dye-sensitized photocatalytic systems (DSPs) have been extensively investigated for solar-driven hydrogen (H2 ) evolution. However, their application in carbon dioxide (CO2 ) reduction remains limited. Furthermore, current solar-driven CO2 -to-CO DSPs typically employ rhenium complexes as catalysts. In this study, we have developed DSPs that incorporate noble metal-free components, specifically a zinc-porphyrin as photosensitizer (PS) and a cobalt-quaterpyridine as catalyst (CAT). Taking a significant stride forward, we have achieved an antenna effect for the first time in CO2 -to-CO DSPs by introducing a Bodipy as an additional chromophore to enhance light harvesting efficiency. The energy transfer from Bodipy to zinc porphyrin resulted in remarkable stability (turn over number (TON)=759 vs. CAT), and high CO evolution activity (42 mmol g-1  h-1 vs. CAT).

Solvent-Dependent Functional Aggregates of Unsymmetrical Squaraine Dyes on TiO2 Surface for Dye-Sensitized Solar Cells

Alkyl group wrapped donor-acceptor-donor (D-A-D) based unsymmetrical squaraine dyes SQ1, SQ5, and SQS4 were used to evaluate the effect of sensitizing solvents on dye-sensitized solar cell (DSSC) efficiency. A drastic change in DSSC efficiency was observed when the photo-anodes were sensitized in acetonitrile (bad solvent when considering dye solubility) and chloroform (good solvent) with an Iodolyte (I^-/I₃^-) electrolyte. The DSSC device sensitized with squaraine dyes in acetonitrile showed better photovoltaic performance with enhanced photocurrent generation and photovoltage compared to the device sensitized in chloroform. In a good sensitizing solvent, dyes with long hydrophobic alkyl chains are deleterious forming aggregates on the TiO₂ surface, which results in an incident photon-to-current conversion efficiency (IPCE) response mostly from monomeric and dimeric structures. Meanwhile, a bad sensitizing solvent facilitates the formation of well-packed self-assembled structures on the TiO₂ surface, which are responsible for a broad IPCE response and high device efficiencies. The photoanode sensitized in the bad sensitizing solvent showed enhanced V_OC values of 642, 675, and 699 mV; J_SC values of 6.38, 11.1, and 11.69 mA/cm²; and DSSC device efficiencies of 3.0, 5.63, and 6.13% for the SQ1, SQ5, and SQS4 dyes in the absence of a coadsorbent (chenodeoxycholic acid (CDCA)), respectively, which were further enhanced by CDCA addition. Meanwhile, the photoanode sensitized in the good sensitizing solvent showed relatively low photovoltaic V_OC values of 640, 652, and 650 mV; J_SC values of 5.78, 6.79, and 6.24 mA/cm²; and device efficiencies of 2.73, 3.35, and 3.20% for SQ1, SQ5, and SQS4 in the absence of CDCA, respectively, which were further varied with equivalents of CDCA. The best DSSC device efficiencies of 6.13 and 3.20% were obtained for SQS4 without CDCA, where the dye was sensitized in acetonitrile (bad) and chloroform (good) sensitizing solvents, respectively.

New porphyrin photosensitizers-Synthesis, singlet oxygen yield, photophysical properties and application in PDT

This research on porphyrin-based photosensitizer system has a very important theoretical and practical significance in the photodynamic therapy (PDT) treatment of cancer. Based on this, in this article, a series of porphyrin derivatives were first designed and synthesized, and a "push-pull" porphyrin photosensitizer with two symmetrical ethanethioate groups was finally constructed. Based on the characterization of their chemical structures (¹H and¹³C NMR, MS, IR, and UV-Vis spectroscopy) and the use of the density functional theory (DFT) and time-dependent DFT (TDDFT) to address the nature of the excited states as well as the dark/phototoxicity, the results have indicated the relationship between the porphyrin structure and properties. The experimental and theoretical UV-Vis absorption properties of porphyrins were discussed. The four porphyrin compounds synthesized all demonstrated a high capacity to generate singlet oxygen under long-wavelength (590 nm) light and low dark toxicity. Compared with the conventional porphyrin photosensitizers, P4 with a CT band (from 580 to 750 nm) is beneficial to the penetration of the light, presenting the potential for applications in PDT.

A promising anticancer drug: a photosensitizer based on the porphyrin skeleton

Photodynamic therapy (PDT) is a minimally invasive combination of treatments that treat tumors and other diseases by using photosensitizers, light and oxygen to produce cytotoxic reactive oxygen species (ROS) inducing tumor cell apoptosis. Photosensitizers are the key part of PDT for clinical application and experimental research, and most of them are porphyrin compounds at present. Due to their unique affinity for tumor tissues, porphyrins are not only excellent photosensitizers, but also good carriers to transport other active drugs into tumor tissues, which can exert synergistic anticancer effects of PDT and chemotherapy. This article reviews the clinical development of porphyrin photosensitizers and the research status of porphyrin containing bioactive groups. Finally, future perspectives and the current challenges of photosensitizers based on the porphyrin skeleton are discussed.

Bilayer Adsorption of Porphyrin Molecules Substituted with Carboxylic Acid atop the NN4A Network Revealed by STM and DFT

Bottom-up technology is a bridge connecting a two-dimensional (2D) monolayer structure with a three-dimensional (3D) bulk structure. From 2D to 3D, it helps us to understand the driving force of an organization process to control the molecular arrangement in the 3D phase. Here, we aimed at the fabrication of multilayer nanostructures on solid substrates. Bis(3,5-diacidic)diazobenzene (NN4A) was chosen as one molecule because of its photosensitive azo group and carboxylic group possessing hydrogen bonding effect, while porphyrin molecules composed of different numbers and positions of carboxylic acid groups were used as the other component. It was found that the porphyrin molecules could adopt different adsorption configurations because of the influence of carboxylic groups, leading to different subsequent coassemblies on the solid surface. The NN4A/porphyrin systems underwent structural transformation when NN4A molecules were adsorbed on the highly oriented pyrolytic graphite surface with predeposited porphyrin. This work displayed an efficient method on the construction of multilayer nanostructures in the molecular surface engineering and provided a new way to construct 3D structures based on the molecular design.

Push-Pull Zinc Porphyrins as Light-Harvesters for Efficient Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSSC) has been attractive to scientific community due to its eco-friendliness, ease of fabrication, and vivid colorful property etc. Among various kinds of sensitizers, such as metal-free organic molecules, metal-complex, natural dyes etc., porphyrin is one of the most promising sensitizers for DSSC. The first application of porphyrin for sensitization of nanocrystaline TiO2 can be traced back to 1993 by using [tetrakis(4-carboxyphenyl) porphyrinato] zinc(II) with an overall conversion efficiency of 2.6%. After 10 years efforts, Officer and Grätzel improved this value to 7.1%. Later in 2009, by constructing porphyrin sensitizer with an arylamine as donor and a benzoic acid as acceptor, Diau and Yeh demonstrated that this donor-acceptor framwork porphyrins could attain remarkable photovoltaic performance. Now the highest efficiencies of DSSC are dominated by donor-acceptor porphyrins, reaching remarkable values around 13.0% with cobalt-based electrolytes. This achievement is largely contributed by the structural development of donor and acceptor groups within push-pull framwork. In this review, we summarized and discussed the developement of donor-acceptor porphyrin sensitizers and their applications in DSSC. A dicussion of the correlation between molecular structure and the spectral and photovoltaic properties is the major target of this review. Deeply dicussion of the substitution group, especially on porphyrin's meso-position were presented. Furthermore, the limitations of DSSC for commercialization, such as the long-term stability, sophisticated synthesis procedures for high efficiency dye etc., have also been discussed.

Interplay between π-Bridges and Positions of Branched Alkyl Groups of Unsymmetrical D-A-D-π-A Squaraines in Dye-Sensitized Solar Cells: Mode of Dye Anchoring and the Charge Transfer Process at the TiO2/Dye/Electrolyte Interface

Far-red-absorbing squaraines possessing high molar absorptivity (>10⁵ M^-1 cm^-1) are being attracted as high-efficiency chromophores in dye-sensitized solar cells (DSSCs). A series of donor-acceptor-donor-π spacer-acceptor (D-A-D-π-A) unsymmetrical squaraines, PSQ1-5, with indoline donor and squaric/cyanoacetic acid acceptor units, were designed for sensitized solar cells. For extending the absorption toward the near-infrared region (NIR) and controlling the orientation on the TiO₂ surface, benzene (PSQ1 and PSQ2) and thiophene (PSQ3-5) π-spacers and out-of-plane branched alkyl groups at the indoline that are away (PSQ1, PSQ3, and PSQ5) or near (PSQ2 and PSQ4) the anchoring group, respectively, were introduced. Dynamic aggregation tendency of PSQ1 and PSQ3 than that of their isomers systematically modulates the orientation on the TiO₂ surface, which in turn enhances photovoltaic performance. Absorptance on a thin transparent TiO₂ film shows a visible-to-NIR response with an onset around 800 nm for PSQ3-5. Although there is close resemblance in electrochemical redox levels, their high injection efficiency and recombination resistance differentiated their impact on the way of anchoring and the dihedral angle between D-A-D units and π-spacers. DSSCs sensitized with PSQ5 achieved a PCE of 8.15% under simulated AM 1.5G illumination (100 mW cm^-2), with the current density (J_sc) and open-circuit voltage (V_oc) of 19.73 mA cm^-2 and 630 mV, respectively. A clear comparison of the incident-photon-to-current conversion efficiency versus the light-harvesting efficiency correlates the structure-property relationship with J_sc obtained for PSQ dyes. Electrochemical impedance spectroscopy was carried out to examine the TiO₂/dye/electrolyte interface for further confirmation of the enhanced PCE of top-sp³-alkylated PSQ5 over that of other dyes.

A Hydroxamic Acid Anchoring Group for Durable Dye-Sensitized Solar Cells Incorporating a Cobalt Redox Shuttle

A hydroxamic acid group has been employed for the first time as an anchoring group for cobalt-based dye-sensitized solar cells (DSSCs). The porphyrin dye YD2-o-C8HA including a hydroxamic acid anchoring group exhibited a power conversion efficiency (η) of 6.4 %, which is close to that of YD2-o-C8, a representative porphyrin dye incorporating a conventional carboxylic acid. More importantly, YD2-o-C8HA was found to be superior to YD2-o-C8 in terms of both binding ability to TiO₂ and durability of cobalt-based DSSCs. Notably, YD2-o-C8HA photocells revealed a higher η-value (4.1 %) than YD2-o-C8 (2.8 %) after 500 h illumination. These results suggest that the hydroxamic acid can be used for DSSCs with other transition-metal-based redox shuttle to ensure high cell durability as well as excellent photovoltaic performance.

Synthesis and spectral evaluation of 5,10,15,20-tetrakis(3,4-dibenzyloxyphenyl)porphyrin

Porphyrins are of interest in many applications that involve electron transfer and absorption of light, such as solar energy and photodynamic cancer therapy. The newly synthesized 5,10,15,20-tetrakis(3,4-dibenzyloxyphenyl)porphyrin, TDBOPP, was characterized using 1H NMR, 13C NMR, UV-vis and fluorescence spectroscopy and MALDI-TOF/TOF high resolution mass spectrometry. Standard 1H NMR and 13C NMR experiments coupled with nuclear Overhauser effect (NOE) experiments confirmed the structure of the compound. The expected M+ and [M+H]+ ions are observed in the MALDI-TOF/TOF mass spectrum. The UV-vis absorption spectrum of TDBOPP shows a Soret band at 424 nm and three Q bands at 519 nm, 556 nm, and 650 nm with molar absorptivity 3.6×105 cm−1m−1, 1.6×104 cm−1m−1, 1.0×104 cm−1m−1 and 5.3×103 cm−1m−1, respectively. Excitation at 424 nm gives emission at 650 nm. The quantum yield of the porphyrin is 0.11.

Novel porphyrin-preparation, characterization, and applications in solar energy conversion

Accelerated inner charge transfer in porphyrins promotes a broad light-harvesting ability up to 840 nm and a conversion efficiency of 9.2%.