Systematic Investigations on the Roles of the Electron Acceptor and Neighboring Ethynylene Moiety in Porphyrins for Dye-Sensitized Solar Cells

Recent advances in the approaches for improving the photovoltaic performance of porphyrin-based DSSCs

Among other photovoltaic techniques including perovskite solar cells and organic solar cells, dye-sensitized solar cells (DSSCs) are considered to be a potential alternative to conventional silicon solar cells. Porphyrins are promising dyes with the properties of easy modification and superior light-harvesting capability. However, porphyrin dyes still suffer from a number of unfavorable aspects, which need to be addressed in order to improve the photovoltaic performance. This feature article briefly summarizes the recent progress in improving the Voc and Jsc of porphyrin-based DSSCs in terms of molecular engineering by modifying the porphyrin macrocycle, donor and acceptor moieties of the porphyrin dyes, coadsorption of the porphrin dyes with bulky coadsorbents like chenodeoxycholic acid (CDCA), and cosensitization of the porphyrin dyes with metal-free organic dyes. Notably, concerted companion (CC) dyes are described in detail, which have been constructed by linking a porphyrin dye subunit and a metal-free organic dye subunit with flexible alkoxy chains to achieve panchromatic absorption and concerted enhancement of Voc and Jsc. In one sentence, this article is expected to provide further insights into the development of high performance DSSCs through the design and syntheses of efficient porphyrin dyes and CC dyes in combination with device optimization to achieve simultaneously elevated Voc and Jsc, which may inspire and promote further progress in the commercialization of the DSSCs.

Nanostructured Aluminum Oxyhydroxide-A Prospective Support for Functional Porphyrin-Based Materials

A method for the grafting of unsymmetrical A2BC-type 5,15-bis(4-butoxyphenyl)-10-(4-carboxyphenyl)-20-(phenanthrenoimidazolyl)-porphyrin onto the surface of nanostructured aluminum oxyhydroxide modified with a single SiO2 layer (NAOM) was successfully developed. A straightforward procedure towards surface modification of NAOM allowed us to prepare a new porphyrin-containing hybrid material. The obtained 3D heterostructure was extensively characterized using XPS, TEM and diffuse reflectance spectroscopy. Structural and morphological peculiarities of the inorganic support before and after the immobilization procedure were studied and discussed in detail. The stability of the material against leaching and the porphyrin immobilization ratio ca. 14% by weight were also revealed.

Fluorenyl Indoline as an Efficient Electron Donor for Concerted Companion Dyes: Enhanced Light-Harvesting and Photocurrent

Concerted companion dyes (CC dyes) like XW61 have been demonstrated to be an effective platform for developing efficient DSSCs. However, the moderated phenothiazine-based electron donor in XW61 results in unsatisfactory J_sc. To address this problem, a stronger fluorenyl indoline-based electron donor has been used to construct porphyrin dye XW68 and organic dyes Y1-Y2. The stronger electron-donating character of the fluorenyl indoline unit leads to an enhanced J_sc value (20.48 mA·cm^-2) for the individual dye XW68. On this basis, CC dyes XW69-XW70-C8 have been designed and synthesized by combining the frameworks of Y1 and Y2 with XW68. The complementary absorption characters of the porphyrin and the organic dye moieties lead to panchromatic absorption with a strong light-harvesting capability from 350 to 700 nm and the onset wavelength extended to ca. 840 nm in the IPCE curves. As a result, excellent J_sc values have been achieved (>22 mA·cm^-2). In addition to the advantages of high J_sc, bulky octyl groups have been introduced into the donor of XW70-C8 to reduce dye aggregation and suppress charge recombination. Finally, a highest PCE of 11.1% with a satisfactory J_sc (22.25 mA·cm^-2) and an enhanced V_oc (750 mV) has been achieved upon coadsorption of XW70-C8 with CDCA. In addition, the CC dye XW70-C8-based solar cells exhibit excellent long-term photostability. These results provide an effective method for rationally improving the photovoltaic behavior, especially the J_sc of CC dyes, by introducing strong electron donor moieties with suitable substituents.

Novel anthracene-based organic dyes as co-sensitizers of porphyrins for developing efficient dye-sensitized solar cells

A high efficiency of 10.22% has been achieved through the cosensitization of anthracene-based organic dyes with a porphyrin dye.

Light-Absorbing Pyridine Derivative as a New Electrolyte Additive for Developing Efficient Porphyrin Dye-Sensitized Solar Cells

To fabricate efficient dye-sensitized solar cells (DSSCs), 4-tert-butylpyridine (TBP) is commonly used as an additive in the electrolytes for improving the photovoltages (V_OC). However, TBP cannot play a positive role in improving the photocurrent (J_SC) because of the lack of absorption in the visible-wavelength range. We herein report a light-absorbing pyridine derivative N1 as an additive for the axial coordination with porphyrin dyes. N1 was synthesized by introducing a (bis(4-methoxyphenyl)amino)anthryl moiety into the para-position of pyridine via an acetylene bridge, and porphyrin dye XW64 containing meso-3,5-disubstituted phenyl groups was synthesized considering that the meta-substituted phenyl groups may induce weaker steric hindrance with the axial pyridyl ligand, as compared with wrapped and strapped porphyrin dyes. Thus, N1 was used as an electrolyte additive together with TBP. When optimized concentrations of 6 mM N1 and 0.5 M TBP were used for fabricating DSSCs based on XW64, enhanced photovoltaic performance was achieved, with J_SC, V_OC, and efficiency of 15.65 mA·cm^-2, 0.701 V, and 7.35%, respectively, superior to those of the corresponding DSSCs without using the additives (J_SC = 14.86 mA·cm^-2, V_OC = 0.599 V, and efficiency = 5.94%). The enhancement of J_SC can be ascribed to the improved light-harvesting ability induced by the axially coordinated N1. Furthermore, the two additives also can be used to fabricate efficient solar cells based on the wrapped porphyrin dye XW42, achieving high efficiency of 10.3%, indicative of their general applicability in fabricating high-performance DSSCs. These results indicate that the simultaneous employment of the traditional TBP additive and a pyridyl ligand with light-harvesting ability in the electrolyte for the axial coordination to a porphyrin dye is a promising approach for developing efficient DSSCs.

Theoretical Study of the Effect of π-Bridge on Optical and Electronic Properties of Carbazole-Based Sensitizers for DSSCs

Eight novel metal-free organic sensitizers were proposed for dye-sensitized solar cells (DSSCs), theoretically calculated and studied via density functional theory with D-π-A structure. These proposals were formed to study the effect of novel π-bridges, using carbazole as the donor group and cyanoacrylic acid as the anchorage group. Through the M06/6-31G(d) level of theory, ground state geometry optimization, vibrational frequencies, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, and their energy levels were calculated. Further, chemical reactivity parameters were obtained and analyzed, such as chemical hardness (η), electrophilicity index (ω), electroaccepting power (ω+) and electrodonating power (ω-). Free energy of electron injection (ΔGinj) and light-harvesting efficiency (LHE) also were calculated and discussed. On the other hand, absorption wavelengths, oscillator strengths, and electron transitions were calculated through time-dependent density functional theory with the M06-2X/6-31G(d) level of theory. In conclusion, the inclusion of thiophene groups and the Si heteroatom in the π-bridge improved charge transfer, chemical stability, and other optoelectronic properties of carbazole-based dyes.

A new type of multibenzyloxy-wrapped porphyrin sensitizers for developing efficient dye-sensitized solar cells

Porphyrin dyes have been widely used for the fabrication of efficient dye-sensitized solar cells (DSSCs). However, dye aggregation and charge recombination still exert negative effects on photovoltaic performance, resulting in unsatisfactory power conversion efficiencies (PCEs). Herein, we report a new class of porphyrin sensitizers, XW52 and XW53 employing four benzyloxy groups to wrap the porphyrin cores. As a result, an efficiency of 7.6% was obtained for XW52, with [Formula: see text] and [Formula: see text] of 668 mV and 16.63 mA cm[Formula: see text], respectively. Compared with XW52, an additional 2,6-dialkoxyphenyl group has been introduced to the N-atom of the phenothiazine donor to furnish XW53 with the aim to further improve the anti-aggregation character and the solubility, and thus the [Formula: see text] was improved to 674 mV, and a higher efficiency of 7.9% was achieved for XW53. Upon cosensitization with PT-C6, the[Formula: see text] and [Formula: see text] were synergistically enhanced to 727 mV and 18.67 mA cm[Formula: see text], respectively. As a result, a high efficiency of 9.6% was successfully achieved for the cosensitization system of XW53 + PT-C6. These results provide an effective novel strategy for designing efficient porphyrin dyes by introducing multiple benzyloxy groups to the meso-phenyl groups.

Solar Cells Sensitized with Porphyrin Dyes Containing Oligo(Ethylene Glycol) Units: A High Efficiency Beyond 12

A series of new porphyrin dyes (XW42-XW44) containing oligo(ethylene glycol) units have been designed and synthesized. Two triethylene glycol units were introduced into the phenothiazine moiety of XW42, whereas diethylene glycol (DEG) and ethylene glycol chains were introduced to afford XW43 and XW44, respectively. Interestingly, the efficiencies of the DSSCs were clearly dependent on the chain lengths. Among the three dyes, XW42 and XW43 exhibited relatively high open-circuit voltages of 751 and 750 mV, respectively, and XW43 exhibited the highest efficiency of 10.32 % owing to the presence of the DEG chains with suitable lengths and excellent ability to trap Li⁺ . Furthermore, through a combined coadsorption and cosensitization approach, the efficiencies were dramatically enhanced. As a result, a highest efficiency of 12.10 % was obtained for the XW43+chenodeoxycholic acid+PT-C6 (a metal-free organic dye) system, which ranks among the highest efficiencies of cells based on the traditional iodine electrolyte.

Multiply Wrapped Porphyrin Dyes with a Phenothiazine Donor: A High Efficiency of 11.7% Achieved through a Synergetic Coadsorption and Cosensitization Approach

Photocurrent ( J_sc) and photovoltage ( V_oc) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel porphyrin dyes, XW36-XW39, using an N-phenyl-substituted phenothiazine donor to pursue higher PCE. For XW36 and XW37, the N-phenyl group is wrapped with two ortho-alkoxy chains. In contrast, it is substituted with a para-alkoxy group in XW38 and XW39. The phenothiazine wrapping in XW36 and XW37 induces more serious distortion, which is beneficial for anti-aggregation but unfavorable for the electron transfer from donor to a porphyrin framework. Thus, individual porphyrin dyes XW36 and XW37 exhibit efficiencies of 9.05 and 9.58%, respectively, lower than those of 9.51 and 10.0% achieved for XW38 and XW39, respectively. Besides, the introduction of a methyl group into a benzoic acid acceptor unit is conducive to anti-aggregation and thus improves the V_oc and efficiencies. Therefore, higher efficiencies were achieved for XW37 and XW39, compared with XW36 and XW38, respectively. Interestingly, although the individual XW36 dye shows a lowest efficiency among the four dyes, a highest efficiency of 11.7% was obtained for XW36 on the basis of synergetic adsorption with chenodeoxycholic acid and PT-C6 because of simultaneously improved J_sc and V_oc, which may be ascribed to the lowest dye-loading amount of XW36 among all of these porphyrin dyes, with the largest vacancy area left on the TiO₂ surface available for cosensitizer PT-C6, resulting in a highest J_sc. The high efficiency of 11.7% is one of the highest efficiencies using I^-/I₃^- electrolytes in DSSCs. These results provide an effective strategy for developing efficient DSSCs by the targeted coadsorption and cosensitization of porphyrin sensitizers optimized through introducing a bis( ortho-alkoxy)-wrapped phenyl group into the phenothiazine donor and/or methyl groups into the benzoic acid acceptor unit.

Organic Sensitizers with Extended Conjugation Frameworks as Cosensitizers of Porphyrins for Developing Efficient Dye-Sensitized Solar Cells

Relatively high efficiencies have been achieved for porphyrin-based dye-sensitized solar cells. For the purpose of designing efficient cosensitizers, we herein report systematically optimized dyes XC1-XC5 employing a triphenylamine donor, a benzothiadiazole moiety as the auxiliary acceptor, and a benzoic acid acceptor. One hexyl and four hexyloxy groups were introduced, and an ethynylene moiety was introduced between the donor and the auxiliary acceptor to afford XC1. To further extend the absorption wavelength, a second ethynylene moiety was introduced between the acceptor and the auxiliary acceptor to afford XC2. XC3 and XC4 were designed by introducing one and two methyl substituents, respectively, into the meta-positions of the anchoring carboxyl group. XC5 was further synthesized by inserting a cyano substituent into one of the ortho-positions of the carboxyl group with the purpose to strengthen the intramolecular charge-transfer effect and thus broaden the absorption wavelength. As expected, compared with the J_sc (14.29 mA·cm^-2) of XC1, the corresponding J_sc values for XC2-XC5 were enhanced to 16.50, 16.95, 16.73, and 17.74 mA·cm^-2, respectively. Moreover, XC4 exhibits the highest V_oc of 770 mV owing to the presence of a maximum of seven chains, which can effectively suppress dye aggregation. As a result, compared with XC1, XC2-XC5 exhibit improved efficiencies of 8.67, 9.05, 8.78, and 9.30%, respectively. In addition, the efficiencies of XC3 and XC5 were further enhanced by cosensitizing them with our previously reported porphyrin dye XW28 under various conditions. Finally, a remarkable efficiency of 10.50% was achieved for the cells cosensitized with XC5 and XW28. These results indicate that the combination of good planarity of the extended D-π-A framework with multiple alkoxy/alkyl chains may compose an effective optimizing strategy for designing and synthesizing excellent cosensitizers for porphyrins.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Porphyrin-sensitized solar cells: systematic molecular optimization, coadsorption and cosensitization

As a promising low-cost solar energy conversion technique, dye-sensitized solar cells have undergone spectacular development since 1991. For practical applications, improvement of power conversion efficiency has always been one of the major research topics. Porphyrins are outstanding sensitizers endowed with strong sunlight harvesting ability in the visible region and multiple reaction sites available for functionalization. However, judicious molecular design in consideration of light-harvest, energy levels, operational dynamics, adsorption geometry and suppression of back reactions is specifically required for achieving excellent photovoltaic performance. This feature article highlights some of the recently developed porphyrin sensitizers, especially focusing on the systematic dye structure optimization approach in combination with coadsorption and cosensitization methods in pursuing higher efficiencies. Herein, we expect to provide more insights into the structure-performance correlation and molecular engineering strategies in a stepwise manner.

Synthesis and characterization of zinc carboxy–porphyrin complexes for dye sensitized solar cells

DOTA-like porphyrin Zn complexes 8 afford new perspectives in DSSCs compared to mono-porphyrin counterpart 2, by displaying a PCE (%) of 7.13.

Theoretical design of porphyrin sensitizers with different acceptors for application in dye-sensitized solar cells

Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, three porphyrin dyes with different acceptors, such as carboxylic acid, cyanoacrylic acid, and 2-cyano-N-hydroxyacrylamide, have been designed. Compared to the best sensitizer (YD2-o-C8) so far, these designed dyes have small highest occupied orbital to lowest unoccupied orbital (HOMO–LUMO) band gaps, and wide absorptions with large oscillator strength at porphyrin Q bands. And the designed Dye1 is similar to YD2-o-C8 in electronic coupling with TiO₂, while improved Dye2 and Dye3 are better than YD2-o-C8, thus, Dye2 and Dye3 will be much faster for electron injection in dye-sensitized solar cell systems based on their long-term stable and efficient anchor groups. All these features show that our designed dyes, especially Dye2 and Dye3, have better absorption performance and faster electron injection. In addition, our results point out that 2-cyano-N-hydroxyacrylamide is a new promising acceptor. This study is expected to assist the molecular design of new efficient dyes for the advancement of dye-sensitized solar cells.

Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, three porphyrin dyes with different acceptors, such as carboxylic acid, cyanoacrylic acid, and 2-cyano-N-hydroxyacrylamide, have been designed.

Efficient Solar Cells Based on Porphyrin Dyes with Flexible Chains Attached to the Auxiliary Benzothiadiazole Acceptor: Suppression of Dye Aggregation and the Effect of Distortion

Donor-π-acceptor-type porphyrin dyes have been widely used for the fabrication of efficient dye-sensitized solar cells (DSSCs) owing to their strong absorption in the visible region and the ease of modifying their chemical structures and photovoltaic behavior. On the basis of our previously reported efficient porphyrin dye XW11, which contains a phenothiazine-based electron donor, a π-extending ethynylene unit, and an auxiliary benzothiadiazole acceptor, we herein report the syntheses of novel porphyrin dyes XW26-XW28 by introducing one or two alkyl/alkoxy chains into the auxiliary acceptor. The introduced chains can effectively suppress dye aggregation. As a result, XW26-XW28 show excellent photovoltages of 700, 701, and 711 mV, respectively, obviously higher than 645 mV obtained for XW11. Nevertheless, the optimized structures of XW26 and XW27 exhibit severe distortion, showing large dihedral angles of 57.2° and 44.0°, respectively, between the benzothiadiazole and benzoic acid units, resulting from the steric hindrance between the benzoic acid unit and the neighboring alkyl/alkoxy chain on the benzothiadiazole unit, and thus blue-shifted absorption, decreased photocurrents. and low efficiencies of 5.19% and 6.42% were observed for XW26 and XW27, respectively. Interestingly, XW26 exhibits a more blue-shifted absorption spectrum relative to XW27, indicating that the steric hindrance of the alkyl/alkoxy chains has a more pronounced effect than the electronic effect. Different from XW26 and XW27, XW28 contains only one alkyl chain neighboring the ethynylene unit, which does not induce obvious steric hindrance with the benzoic acid unit, and thus distortion of the molecule is not seriously aggravated compared with XW11. Hence, its absorption spectrum and photocurrent are similar to those of XW11. As a result, a higher efficiency of 9.12% was achieved for XW28 because of its suppressed dye aggregation and higher photovoltage. It is worth noting that a high efficiency of 10.14% was successfully achieved for XW28 upon coadsorption with CDCA, which is also higher than the corresponding efficiency obtained for XW11. These results provide a novel approach for developing efficient porphyrin dyes by introducing chains into the suitable position of the auxiliary benzothiadiazolyl moiety to suppress dye aggregation, without seriously aggravating distortion of the dye molecules.

Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A[Formula: see text]B and A[Formula: see text] free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies ([Formula: see text] of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4[Formula: see text]-pyridyl)-20-(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]TriPyMCPP), 5,10,15,20-tetrakis(4[Formula: see text]-aminophenyl)porphyrin (H[Formula: see text]TAPP) and 5-(4[Formula: see text]-pyridyl)-10,15,20-tris(4[Formula: see text]-carboxyphenyl)porphyrin (H[Formula: see text]MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are shown to be superior sensitizers as compared to carboxyphenylporphyrins. The investigation of effect of functional group and position of functional group of porphyrin dye on DSSC can serve as an important tool to guide further selection and synthesis of potential candidates as sensitizers.

Novel self-assembly with zinc porphyrin via axial coordination for dye-sensitized solar cells

Two zinc porphyrins substituted at the meso-positions with different donor units (denoted as ZnP1 and ZnP2) have been designed and synthesized to construct new self-assemblies (denoted as ZnPx-ZnPA) with anchor porphyrin (ZnPA) dyads formed by the coordination bonds of Zn-to-ligand approach. Then these assemblies were absorbed on the semiconducting TiO2 electrode surfaces by the carboxylic groups of anchor porphyrin (ZnPA) to build dye sensitized solar cells. Their spectral properties, electrochemical, theoretical calculations and photovoltaic properties were systematically investigated. Interestingly, these self-assemblies devices compared to monomer anchoring porphyrin device showed higher [Formula: see text] and [Formula: see text]. Especially, the dyad of ester-based zinc porphyrin (ZnP2) assembly device has the highest photoelectric conversion efficiency. The assembled modes of the assemblies immobilized on TiO2 electrode surfaces were also verified by transmission electron microscopy (TEM).

A detailed experimental and theoretical investigation of the role of cyano groups in the π-bridged acceptor of sensitizers for use in dye-sensitized solar cells (DSCs)

Porphyrin sensitizers LX1, LX2 and LX3 were synthesized for use in DSCs and their electronic properties with TiO₂ were investigated in detail using theoretical calculations.

Significant enhancement in the performance of porphyrin for dye-sensitized solar cells: aggregation control using chenodeoxycholic acid

CDCA co-sensitizers prevent aggregation of the dyes on the TiO₂ surface.

Novel Blue Organic Dye for Dye-Sensitized Solar Cells Achieving High Efficiency in Cobalt-Based Electrolytes and by Co-Sensitization

Blue and green dyes as well as NIR-absorbing dyes have attracted great interest because of their excellent ability of absorbing the incident photons in the red and near-infrared range region. A novel blue D-π-A dye (Dyenamo Blue), based on the diketopyrrolopyrrole (DPP)-core, has been designed and synthesized. Assembled with the cobalt bipyridine-based electrolytes, the device with Dyenamo Blue achieved a satisfying efficiency of 7.3% under one sun (AM1.5 G). The co-sensitization strategy was further applied on this blue organic dye together with a red D-π-A dye (D35). The successful co-sensitization outperformed a panchromatic light absorption and improved the photocurrent density; this in addition to the open-circuit potential result in an efficiency of 8.7%. The extended absorption of the sensitization and the slower recombination reaction between the blue dye and TiO₂ surface inhibited by the additional red sensitizer could be the two main reasons for the higher performance. In conclusion, from the results, the highly efficient cobalt-based DSSCs could be achieved with the co-sensitization between red and blue D-π-A organic dyes with a proper design, which showed us the possibility of applying this strategy for future high-performance solar cells.

Influence of Phenylethynylene of Push-Pull Zinc Porphyrins on the Photovoltaic Performance

A series of zinc porphyrin dyes YD22-YD28 were synthesized and used for dye-sensitized solar cells. Dyes YD26-YD28 consist of zinc porphyrin (ZnP) as core unit, arylamine (Am) as electron-donating group, and p-ethynylbenzoic acid (EBA) as an electron-withdrawing/-anchoring group. The dyes YD22-YD25 contain additional phenylethynylene group (PE) bridged between Am and ZnP units. The influence of the PE unit on molecular properties as well as photovoltaic performances were investigated via photophysical and electrochemical studies and density functional calculations. With the insertion of PE unit, the dyes YD22-YD25 possess better light-harvesting properties in terms of significantly red-shifted Q-band absorption. The conversion efficiencies for dyes YD22-YD25 are better than those of dyes YD26-YD28 owing to larger J(SC) output. Natural transition orbitals and Mulliken charge analysis were used to analyze the electron injection efficiency for porphyrin dyes upon time-dependent DFT calculations. The results indicated that insertion of additional PE unit is beneficial to higher J(SC) by means of improved light-harvesting property due to broadened and red-shifted absorption.

Synthesis and characterization of simple cost-effective trans-A2BC porphyrins with various donor groups for dye-sensitized solar cells

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.

Shifting UV-vis absorption spectrum through rational structural modifications of zinc porphyrin photoactive compounds

Metalloporphyrin assemblies such as Zn–porphyrins are significant photoactive compounds with a number of applications including molecular devices and dye-sensitized solar cells (DSSC).

Synthesis of porphyrin sensitizers with a thiazole group as an efficient π-spacer: potential application in dye-sensitized solar cells

CNU-OC8 exhibits better photovoltaic performance than the benchmark YD2-OC8 sensitizer in a liquid I⁻/I₃⁻ redox electrolyte.

Bilayer structured supramolecular light harvesting arrays based on zinc porphyrin coordination polymers for enhanced photocurrent generation in dye sensitized solar cells

Coordination polymers based on an acylhydrazone zinc porphyrin were synthesized and applied in dye sensitized solar cells for enhanced photocurrent generation.

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%.

Porphyrins Containing a Triphenylamine Donor and up to Eight Alkoxy Chains for Dye-Sensitized Solar Cells: A High Efficiency of 10.9%

Porphyrins are promising DSSC sensitizers due to their structural similarity to chlorophylls as well as their tunable strong absorption. Herein, a novel D-π-A porphyrin dye XW14 containing a strongly electron-donating triphenylamine moiety as the electron donor was designed and synthesized. To avoid undesirably decreased Voc caused by dye aggregation effect, two methoxy or hexyloxy chains were introduced to the para positions of the triphenylamine moiety to afford XW15 and XW16, respectively. To further extend the absorption to a longer wavelength, a benzothiadiazole unit was introduced as an auxiliary acceptor to furnish XW17. Compared with XW14, the introduction of additional methoxy or hexyloxy groups in XW15 and XW16 red-shift the onset wavelengths from 760 to 780 and 790 nm, respectively. More impressively, XW17 has a more extended π-conjugation framework, and thus, it exhibits a much broader IPCE spectrum with an extremely red-shifted onset wavelength of 830 nm, resulting in the highest Jsc (18.79 mA cm(-2)). On the other hand, the hexyloxy chains are favorable for suppressing the dye aggregation effect, and thus XW16 shows the highest Voc of 734 mV. As a result, XW16 and XW17 demonstrate photovoltaic efficiencies of 9.1 and 9.5%, respectively, higher than those of XW14 (8.6%) and XW15 (8.7%), and obviously higher than that of 7.94% for our previously reported dye, XW4. On the basis of optimized porphyrin dye XW17, we used a nonporphyrin dye with a high Voc and strong absorption around 500 nm (WS-5) as the cosensitizer to improve the Voc from 700 to 748 mV, with synergistical Jsc enhancement from 18.79 to 20.30 mA cm(-2). Thus, the efficiency was dramatically enhanced to 10.9%, which is among the highest efficiencies obtained for the DSSCs based on traditional iodine electrolyte. In addition, the DSSCs based on XW17 + WS-5 exhibit good photostability, which is beneficial for practical applications.

Application-oriented computational studies on a series of D-π-A structured porphyrin sensitizers with different electron-donor groups

A series of D-π-A zinc porphyrin sensitizers bearing a substituted iminodibenzyl group at the porphyrin meso position, which is expected to have different electron-donating abilities, were designed. Theoretical studies were performed to examine the photovoltaic properties of these molecules in dye-sensitized solar cells (DSSCs). In particular, the important concepts, the Fukui function and the extended condensed Fukui function, are employed to describe the electron-donating abilities accurately at the quantitative level. Tangui Le Bahers model was adopted to analyze charge transfer (CT) during electron transition. A correlation between the electron donating abilities of the derived iminodibenzyl group and CT was built to evaluate the cell performance based on sensitizers . The theoretical studies showed that porphyrins bearing an extremely strong electron-donating group (EDG) would fail in the generation of photocurrent in the closed circuit when applied in DSSCs due to the higher level of the HOMO energy than the redox potential of the redox couple (I(-)/I3(-)). The one with a weaker EDG () is expected to show better photovoltaic performance than porphyrin with an unsubstituted iminodibenzyl group. This study demonstrates a reliable method involving the employment of the Fukui function, the extended condensed Fukui function and the Tangui Le Bahers model for the evaluation of newly designed D-π-A type porphyrin sensitizers for use in DSSCs, and as guidance for future molecular design.