Efficient Solar Cells Based on Concerted Companion Dyes Containing Two Complementary Components: An Alternative Approach for Cosensitization

Enhanced Efficiency of Dye-Sensitized Solar Cells by Controlled Co-Adsorption Self-Assembly of Dyes

Single dyes typically exhibit limited light absorption in dye-sensitized solar cells (DSSCs). Thus, cosensitization using two or more dyes to enhance light-harvesting efficiency has been explored; however, the aggregation of dyes can adversely affect electron injection capabilities. This study focused on the design and synthesis of three dyes with a common carbazole donor for DSSCs: DZ102, TZ101, and JM102. JM102 broadens the absorption spectrum by replacing the benzoic acid electron acceptor of TZ101 with acetylenic benzoic acid. A cosensitized DSSC device based on CO-1 [DZ102:TZ101 = 1:1 (50 μM:50 μM)] achieved a short-circuit current density of 19.4 mA/cm2 and a power conversion efficiency of 10.9%. For the first time, the molecular interactions between the dyes in the photoanode were demonstrated using cyclic voltammetry, which revealed the presence of intermolecular forces. Adsorption kinetics further indicated that these forces promoted the self-assembly of dyes during adsorption, which resulted in a cosensitization adsorption amount greater than the sum of the individual dye adsorptions. This study provides novel insights into the selection of cosensitizing dyes for DSSCs.

Structural Decoration of Porphyrin/Phthalocyanine Photovoltaic Materials

Porphyrin/phthalocyanine compounds with fascinating molecular structures have attracted widespread attention in the field of solar cells in recent years. In this review, we focus on the pivotal role of porphyrin and phthalocyanine compounds in enhancing the efficiency of solar cells. The review seamlessly integrates the intricate molecular structures of porphyrins and phthalocyanines with their proficiency in absorbing visible light and facilitating electron transfer, key processes in converting sunlight into electricity. By delving into the nuances of intramolecular regulation, aggregated states, and surface/interface structure manipulation, it elucidates how various levels of molecular modifications enhance solar cell efficiency through improved charge transfer, stability, and overall performance. This comprehensive exploration provides a detailed understanding of the complex relationship between molecular design and solar cell performance, discussing current advancements and potential future applications of these molecules in solar energy technology.

Unleashing synergistic co-sensitization of BOA dyes and Ru(ii) complexes for dye-sensitized solar cells: achieving remarkable efficiency exceeding 10% through comprehensive characterization, advanced modeling, and performance analysis

Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative for renewable energy conversion. The synthesis and characterization of the 2-acetonitrile-benzoxazole (BOA) sensitizer MSW-1-4 are presented along with their chemical structures. Four new organic dyes, MSW-1 through MSW-4, were synthesized using BOA as the main building block, with different additional donor groups. The dyes were characterized and their photophysical and electrochemical properties were studied. Computational modeling using density functional theory (DFT) was performed to investigate their potential as sensitizers/co-sensitizers for photovoltaic applications. The modeling showed a distinct charge separation between the donor and acceptor parts of the molecules. For dye-sensitized solar cells, MSW-4 performed the best out of MSW-1-3 and was also better than the reference dye D-5. Moreover, MSW-3 was co-sensitized along with a typical highly efficient bipyridyl Ru(ii) sensitizer, N719, reference dye D-5, and metal-free dye MSW-4, to induce light harvesting over the expanded spectral region and hence improve the efficiency. Co-sensitizer (MSW-3 + N719) showed an improved efficiency of 10.20%. This outperformed a solar cell that used only N719 as the sensitizer, which had an efficiency of 7.50%. The appropriate combined dye loading of MSW-3 + N719 enabled good light harvesting and maximized the photoexcitation. The synergistic effect of using both MSW-3 and N719 as co-sensitizers led to enhanced solar cell performance compared with using N719 alone.

Cascade Radical Pathway-Enabled Nitrogen-Sulfur Coupling: Access to Isothiazolo[3,4-b]-meso-tetraarylporphyrins

A catalyst-free radical-mediated domino strategy for the construction of isothiazolo[3,4-b]-meso-tetraarylporphyrins was developed. During the course of the reaction, 2-benzothioylamino-3-thioformyl-meso-tetraarylporphyrins generated in situ after the addition of Lawesson's reagent to a solution of 2-benzoylamino-3-formyl-meso-tetraarylporphyrins in refluxing toluene underwent a homolytic cleavage to produce nitrogen-sulfur radicals. Subsequently, the formation of a new N-S bond through an intramolecular cascade radical coupling provided direct access to novel β-isothiazole-fused porphyrins.

Panchromatic Light-Harvesting Three-Dimensional Metal Covalent Organic Frameworks for Boosting Photocatalysis

Constructing artificial photocatalysts with panchromatic solar energy utilization remains an appealing challenge. Herein, two complementary photosensitizers, [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) and porphyrin dyes, have been cosensitized in metal covalent organic frameworks (MCOFs), resulting in the MCOFs with strong light absorption covering the full visible spectrum. Under panchromatic light irradiation, the cosensitized MCOFs exhibited remarkable photocatalytic H2 evolution with an optimum rate of up to 33.02 mmol g-1 h-1. Even when exposed to deep-red light (λ = 700 ± 10 nm), a commendable H2 production (0.79 mmol g-1 h-1) was still obtained. Theoretical calculation demonstrated that the [Ru(bpy)3]2+ and porphyrin modules in our MCOFs have a synergistic effect to trigger an interesting dual-channel photosensitization pathway for efficient light-harvesting and energy conversion. This work highlights the potential of combining multiple PSs in MCOFs for panchromatic photocatalysis.

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.

1,1'-Bis-(diphenylphosphino)ferrocene appended d8- and d10-configuration based thiosquarates: the molecular and electronic configurational insights into their sensitization and co-sensitization properties for dye sensitized solar cells

Three new d8- and d10-configuration based 1,1'-bis-(diphenylphosphino)ferrocene (dppf) appended thiosquarates complexes with general composition [M(mtsq)2dppf] (M = Ni2+ (NiL2); Zn2+ (ZnL2) and Cd2+ (CdL2)) (mtsq = 3-ethoxycyclobutenedione-4-thiolate) have been synthesized and characterized spectroscopically as well as in case of NiL2 by single crystal X-ray diffraction technique. The single crystal X-ray analysis reveals square planar geometry around Ni(II) in NiL2, where Ni(II) coordinates with two sulfur centres of two mtsq ligands in monodentate fashion and two phosphorus of a dppf ligand in chelating mode. The supramolecular architecture of NiL2 is sustained by intermolecular C-H⋯O interactions to form one-dimensional chain. Further, the application of these newly synthesized complexes as sensitizers and co-sensitizers/co-absorbents with ruthenium based N719 sensitizer in dye-sensitized solar cells (DSSCs) have been explored. The DSSC set-up based on NiL2 offers best photovoltaic performance with photovoltaic efficiency (η) 5.12%, short-circuit current (Jsc) 11.60 mA cm-2, open circuit potential (Voc) 0.690 V and incident photon to current conversion efficiency (IPCE) 63%. In co-sensitized DSSC set-up, ZnL2 along with state-of-the-art N719 dye displays best photovoltaic performance with η 6.65%, Jsc 14.47 mA cm-2, Voc 0.729 V and IPCE 69%, thereby showing an improvement by 15.25% in photovoltaic efficiency in comparison to the photovoltaic efficiency of N719 sensitized DSSC set-up. Variation in co-sensitization behaviour have been ascribed to the differences in the excited state energy level of co-sensitizers. The ZnL2 and CdL2 have a higher energy level position than N719 dye, allowing efficient electron transfer to N719 during light irradiation, while excited state of NiL2 is lower than N719 dye, preventing photoexcited electron transfer to N719, resulting in its lowest overall efficiency among the three co-sensitized DSSC setups.

Visible-Light-Active Unsymmetrical Squaraine Dyes with Pyridyl Anchoring Groups for Dye-Sensitized Solar Cells

Visible-light-active alkyl group-wrapped unsymmetrical squaraine dyes SD1-SD3 were synthesized, featuring an indoline donor and pyridine and carboxylic acid anchoring groups. Their photophysical, electrochemical, and photovoltaic characteristics were examined by fabricating a dye-sensitized solar cell (DSSC) device. Both carboxylic acid and pyridine anchoring groups containing squaraine dyes SD3 and SD2 possess similar photophysical and electrochemical characteristics. However, their photovoltaic performances were completely different. The SD3 dye with the carboxylic acid anchoring group displayed a DSSC device efficiency of 7.20% (VOC 0.81 V; JSC 12.29 mA/cm2) using iodolyte (I-/I3-) electrolyte, compared to SD1 (VOC 0.659 V; JSC 4.97 mA/cm2; and η - 2.34%) and SD2 (VOC 0.629 V; JSC 1.68 mA/cm2; and η - 0.84%), which were featured with pyridyl anchoring groups. These results were attributed to dye loading on the Lewis and Brønsted acidic sites of TiO2 and the importance of aggregated structures for photocurrent generation. In the incident photon-to-current efficiency (IPCE) analysis, SD1 dye-sensitized devices exhibited photocurrent generation from both monomeric and aggregated dyes on the TiO2 surface. In contrast, SD2 showed photocurrent generation solely from aggregated states. Despite the introduction of long alkyl chains to reduce dye aggregation and charge recombination, the results indicated preferential charge injection from only the aggregated SD2 dye on TiO2. Fluorescence-quenching experiments indicated an efficient charge transfer from the aggregated SD2 dye to TiO2 compared to that of the monomeric dye. Cosensitization, a method to enhance the light-harvesting efficiency and photocurrent generation in DSSCs, was explored by simultaneously cosensitizing pyridyl-based dyes (SD1 and SD2) with a blue-colored carboxylic acid-based squaraine dye SD4. IPCE analysis demonstrated that both SD1 and SD4 contributed to generating a photocurrent of 9.11 mA/cm2. The sequential cosensitization of SD1 and SD4 with the coadsorbent CDCA showed the highest performance, with a VOC of 0.663 V, a JSC of 11.43 mA/cm2, and an efficiency (η) of 5.20%.

A novel central seven-membered BOPYOs: Synthesis, optical properities and optimization of BF2 removal

Many efforts have been made to enrich the variety of BF2 complexes because of their excellent optical properties. However, the investigation on seven-membered ring N, O-chelated BF2 complexes is rare due to their instability with the removal of BF2 unit. Herein, a novel seven-membered ring N, O-chelated BF2 complexes (BOPYOs) with dual-state emission has been synthesized via a facile method. The results of optical properties showed that the fluorescence quantum yield of BOPYO-2 with donor group on 1 and 2-position of 1-indanone unit is much higher than that of BOPYO-1, 3-5 in toluene. The emission spectra of BOPYO-6 or 7 have redshift phenomenon compared with BOPYO-1-5 with weak fluorescence intensity due to their highly distorted structure or intramolecular charge transfer (ICT) effect. BOPYOs show relatively moderate solid emission from orange to deep red color with 596 nm to 686 nm. On the contrary, fluorescence quantum yield of BOPYO-2 in solid is the lowest. The optical properties in solution and solid states are further supported by the single-crystal structure and DFT calculation. Furthermore, the investigation on optimization of BF2 removal shows that the corresponding precursors of BOPYOs could be obtained in protic solvents without adding other catalysts.

β-Pyrrole Functionalized Push or Pull Porphyrins: Excited Charge Transfer Promoted Singlet Oxygen Generation

Singlet oxygen (1O2) producing photosensitizers are highly sought for developing new photodynamic therapy agents and facilitating 1O2-involved chemical reactions. Often singlet oxygen is produced by the reaction of triplet-excited photosensitizers with dioxygen via an energy transfer mechanism. In the present study, we demonstrate a charge transfer mechanism to produce singlet oxygen involving push or pull functionalized porphyrins. For this, 20 β-pyrrole functionalized porphyrins carrying either an electron-rich push or electron-deficient pull group have been newly synthesized. Photoexcitation of these push-pull porphyrins has been shown to produce high-energy MPδ+-Aδ- or MPδ--Dδ+ charge transfer states. Subsequent charge recombination results in populating the triplet excited states of extended lifetimes in the case of the push group containing porphyrins that eventually react with dioxygen to produce the reactive singlet oxygen of relatively higher quantum yields. The effect of the push and pull groups on the porphyrin periphery in governing initial charge transfer, the population of triplet excited states and their lifetimes, and resulting in improved singlet oxygen quantum yields are systematically probed. The improved performance of 1O2 generation by porphyrins carrying push groups is borne out from this study.

Synergistic Effect of Size-Tailored Structural Engineering and Postinterface Modification for Highly Efficient and Stable Dye-Sensitized Solar Cells

Despite significant progress in device performance, dye-sensitized solar cells (DSSCs) continue to fall short of their theoretical potential. Moreover, research in recent years needs to pay more attention to improving the device fabrication process. To achieve the theoretical efficiency limit, it is crucial to optimize the interface between the dye and TiO2 nanoparticles in the entire device stack. Our study indicates that optimizing the structure or size of the coadsorbents and implementing a monolayer adsorption process can be an effective strategy to reduce charge recombination and enhance light-harvesting properties. Our research aims to develop a surface-coating adsorbent plan that controls the TiO2 nanoparticle interface to achieve the radiative limit of power conversion efficiency (PCE). Specifically, we utilized 2-thiophenecarboxylic acid (THCA) or chenodeoxycholic acid (CDCA) as postinterfacial surface-coating adsorbents. Our results demonstrate that this approach effectively achieves the desired PCE limit. Combined with the coadsorbent structure engineering and interface optimization, the device increased the packing area on the TiO2 nanoparticles' surface, reaching an improved PCE of over 13.17% under simulated sunlight (1.5G), which is the highest efficiency of a porphyrin single dye-based DSSC. In particular, this practical approach was also applied to a large-area DSSC with an area of 3 cm2, yielding a remarkable PCE of 9.04%. Furthermore, when applied to a polymer gel electrolyte, this novel approach recorded the highest PCE of 11.16% with a long-term operational stability of up to 1000 h for the quasi-solid-state DSSCs. Our research findings provide a promising avenue for achieving high-performance DSSCs with ease of access and demonstrate practical applications as alternatives to conventional power sources.

Efficient Solar Cells Based on Porphyrin and Concerted Companion Dyes Featuring Benzo 12-Crown-4 for Suppressing Charge Recombination and Enhancing Dye Loading

In recent years, various porphyrin dyes have been designed to develop efficient dye-sensitized solar cells (DSSCs). Based on our previously reported porphyrin dye XW43, which contains a phenothiazine donor with two diethylene glycol (DEG)-derived substituents, we herein report a porphyrin dye XW89 by introducing a benzo 12-crown-4 (BCE) unit onto the N atom of the phenothiazine donor. On this basis, XW90 and XW91 have been synthesized by replacing a DEG chain in XW89 with two DEG chains and a 12-crown-4 unit, respectively. For iodine electrolyte-based DSSCs, dyes XW89-XW91 exhibit VOC values of 765-779 mV, higher than that of XW43 (755 mV), which may be related to the strong capability of the BCE group in binding Li+ and thus suppressing the downward shift of the TiO2 conduction band and interfacial charge recombination. Moreover, the smaller size of 12-crown-4 than the DEG unit enables higher adsorption amounts of the dyes than XW43, contributing to an enhanced JSC value. Due to the presence of two BCE units, dye XW91 exhibits the highest dye loading amount and JSC of 1.86 × 10-7 mol cm-2 and 19.79 mA cm-2, respectively, affording a high PCE of 11.1%. To further enhance the light-harvesting ability, a concerted companion (CC) dye XW92 has been constructed by linking the two subdye units corresponding to the porphyrin dye XW91 and an organic dye. As a result, XW92 affords an enhanced JSC and efficiency. Further coadsorption of XW92 with chenodeoxycholic acid achieved the highest efficiency of 12.1%. This work provides an effective approach for fabricating efficient DSSCs sensitized by porphyrin and CC dyes based on the introduction of crown ether units with smaller sizes and stronger Li+ affinities.

D-π-A Structured Porphyrin and Organic Dyes with Easily Synthesizable Donor Units for Low-Cost and Efficient Dye-Sensitized Solar Cells

This study aimed to develop low-cost D-π-A structured porphyrin and organic dyes with easily synthesizable donor units instead of the conventional complex multistep synthetic donor unit of Hexyloxy-BPFA [bis(7-(2,4-bis(hexyloxy)phenyl)-9,9-dimethyl-9H-fluoren-2-yl)amine] used in SGT-021 and SGT-149 as well-known record cosensitizers with an extremely high power conversion efficiency (PCE). The design strategy concerned the easier synthesis of low-cost donor units with inversion structures in donor groups via donor structural engineering, particularly by changing the position of the fluorene and phenylene units in the donor moiety while keeping the π-bridge and acceptor unit unchanged, leading to the synthesis of two D-π-A structured porphyrins [SGT-021(D0) and SGT-021(D)] and one D-π-A structured organic sensitizer [SGT-149(D)] for dye-sensitized solar cells (DSSCs). Specifically, porphyrin SGT-021(D0) incorporated two hexyl chains into the 9-position of each fluorene, while SGT-021(D) and SGT-149(D) substituted two hexyloxy chain units to the terminal position of each fluorene in the donor groups of porphyrin dyes. The effect of the position of the fluorene and phenylene units in the donor moiety on the photochemical and electrochemical properties, as well as the photovoltaic performance, was compared with the reference dyes of SGT-021 and SGT-149, previously reported by the research group. After optimizing the DSSC devices, SGT-021(D) and SGT-021(D0) achieved a high PCE of 11.6 and 10.5%, respectively, while SGT-149(D) exhibited a little lower PCE of 10.3% under the standard AM 1.5G light intensity. The cell performance of DSSC devices based on SGT-021(D) and SGT-149(D) was inferior to the corresponding reference dyes of SGT-021 and SGT-149 due to their lower donating ability of Hexyloxy-BPFA than Hexyloxy-BFPA.

Advances and prospects of porphyrin derivatives in the energy field

At present, porphyrin is developing rapidly in the fields of medicine, energy, catalysts, etc. More and more reports on its application are being published. This paper mainly takes the ingenious utilization of porphyrin derivatives in perovskite solar cells, dye-sensitized solar cells, and lithium batteries as the background to review the design idea of functional materials based on the porphyrin structural unit in the energy sector. In addition, the modification and improvement strategies of porphyrin are presented by visually showing the molecular structures or the design synthesis routes of its functional materials. Finally, we provide some insights into the development of novel energy storage materials based on porphyrin frameworks.

Sensitizers of Metal Complexes with Sulfur Coordination Achieving a Power Conversion Efficiency of 12.89

In the study to improve the light absorption range and intensity of dye sensitizers in the visible region and promote their photovoltaic performance, five novel polymeric metal complexes with sulfur coordination (BDTT-VBT-Ni, BDTT-VBT-Cu, BDTT-VBT-Zn, BDTT-VBT-Cd, and BDTT-VBT-Hg) to be used as D-A-π-A motif dye sensitizers were designed, synthesized, and characterized. In these polymeric metal complexes with sulfur coordination, the metal complexes with sulfur coordination of benzodithiophene derivatives are used as auxiliary electron acceptors, 8-quinolinol derivatives are used as π-bridge and electron acceptors, and thienylbenzene-[1,2-b:4,5-b'] dithiophene (BDTT) are used as electron donors. The effect of different metal complexes with sulfur coordination on the photovoltaic performance of dye sensitizers has been systematically studied. Under AM 1.5 irradiation (100 mW cm^-2), the devices of dye-sensitized solar cells (DSSCs) based on five polymeric metal complexes with sulfur coordination exhibited a short-circuit current density (J_sc) of 13.43, 15.07, 18.00, 18.99, and 20.78 mA cm^-2, respectively, and their power conversion efficiencies (PCEs) were 7.10, 8.59, 10.68, 11.23, and 12.89%, respectively, and their thermal decomposition temperatures (T_d) were 251, 257, 265, 276, and 277 °C, respectively. The result shows that the J_sc and PCE of five polymeric metal complexes increase by degrees, and the PCE of BDTT-VBT-Hg is up to 12.89%, which is because of the strength of the coordination bonds between Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) and sulfur increases in turn so that the electron-withdrawing ability and electron-transfer ability of auxiliary electron acceptors is enhanced. These results provide a new way to develop stable and efficient metal complexes with sulfur coordination dye sensitizers in the future.

Redox Shuttle-Based Electrolytes for Dye-Sensitized Solar Cells: Comprehensive Guidance, Recent Progress, and Future Perspective

A redox electrolyte is a crucial part of dye-sensitized solar cells (DSSCs), which plays a significant role in the photovoltage and photocurrent of the DSSCs through efficient dye regeneration and minimization of charge recombination. An I^-/I₃ ^- redox shuttle has been mostly utilized, but it limits the open-circuit voltage (V _oc) to 0.7-0.8 V. To improve the V _oc value, an alternative redox shuttle with more positive redox potential is required. Thus, by utilizing cobalt complexes with polypyridyl ligands, a significant power conversion efficiency (PCE) of above 14% with a high V _oc of up to 1 V under 1-sun illumination was achieved. Recently, the V _oc of a DSSC has exceeded 1 V with a PCE of around 15% by using Cu-complex-based redox shuttles. The PCE of over 34% in DSSCs under ambient light by using these Cu-complex-based redox shuttles also proves the potential for the commercialization of DSSCs in indoor applications. However, most of the developed highly efficient porphyrin and organic dyes cannot be used for the Cu-complex-based redox shuttles due to their higher positive redox potentials. Therefore, the replacement of suitable ligands in Cu complexes or an alternative redox shuttle with a redox potential of 0.45-0.65 V has been required to utilize the highly efficient porphyrin and organic dyes. As a consequence, for the first time, the proposed strategy for a PCE enhancement of over 16% in DSSCs with a suitable redox shuttle is made by finding a superior counter electrode to enhance the fill factor and a suitable near-infrared (NIR)-absorbing dye for cosensitization with the existing dyes to further broaden the light absorption and enhance the short-circuit current density (J _sc) value. This review comprehensively analyzes the redox shuttles and redox-shuttle-based liquid electrolytes for DSSCs and gives recent progress and perspectives.

Effect of regio-specific arylamine substitution on novel π-extended zinc salophen complexes: density functional and time-dependent density functional study on DSSC applications

A series of π-extended salophen-type Schiff-base zinc(ii) complexes, e.g., zinc-salophen complexes (ZSC), were investigated toward potential applications for dye-sensitized solar cells. The ZSC dyes adopt linear-, X-, or π-shaped geometries either with the functionalization of 1 donor/1 acceptor or 2 donors/2 acceptors to achieve a push-pull type molecular structure. The frontier molecular orbitals, light-harvesting properties as well as charge transfer characters against regio-specific substitution of donor/acceptor groups were studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results reveal that all ZSC dyes of D-ZnS-π-A geometry (where D, S, and A denote to donor, salophen ligand, and acceptor, respectively) exhibit relatively lower HOMO energy compared to the structurally resembled porphyrin dye YD2-o-C8. Natural transition orbital (NTO) and electron-hole separation (EHS) approaches clearly differentiate the linear type YD-series dyes from CL-, AJ1-, and AJ2-series dyes because of poor charge transfer (CT) properties. In contrast, the π-shaped AJ2-series and X-shaped AJ1-series dyes outperform the others in a manner of stronger CT characteristics, broadened UV-vis absorption as well as tunable bandgap simply via substitution of p-ethynylbenzoic acids (EBAs) and arylamine donors at salophen 7,8- and 2,3,12,13-positions, respectively. Both EHS and calculated exciton binding energies suggest the strength of CT character for ZSC dyes with an amino donor in the trend TPA > AN > DPA. This work has provided clear illustration toward molecular design of efficient dyes featuring a zinc-salophen backbone.

Hydroxamic acid pre-adsorption raises the efficiency of cosensitized solar cells

Dye-sensitized solar cells (DSCs) convert light into electricity by using photosensitizers adsorbed on the surface of nanocrystalline mesoporous titanium dioxide (TiO₂) films along with electrolytes or solid charge-transport materials^1-3. They possess many features including transparency, multicolour and low-cost fabrication, and are being deployed in glass facades, skylights and greenhouses⁴. Recent development of sensitizers^5-10, redox mediators^11-13 and device structures¹⁴ has improved the performance of DSCs, particularly under ambient light conditions^14-17. To further enhance their efficiency, it is pivotal to control the assembly of dye molecules on the surface of TiO₂ to favour charge generation. Here we report a route of pre-adsorbing a monolayer of a hydroxamic acid derivative on the surface of TiO₂ to improve the dye molecular packing and photovoltaic performance of two newly designed co-adsorbed sensitizers that harvest light quantitatively across the entire visible domain. The best performing cosensitized solar cells exhibited a power conversion efficiency of 15.2% (which has been independently confirmed) under a standard air mass of 1.5 global simulated sunlight, and showed long-term operational stability (500 h). Devices with a larger active area of 2.8 cm² exhibited a power conversion efficiency of 28.4% to 30.2% over a wide range of ambient light intensities, along with high stability. Our findings pave the way for facile access to high-performance DSCs and offer promising prospects for applications as power supplies and battery replacements for low-power electronic devices^18-20 that use ambient light as their energy source.

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.

Influence of the π-Bridge-Fused Ring and Acceptor Unit Extension in D-π-A-Structured Organic Dyes for Highly Efficient Dye-Sensitized Solar Cells

Three new D-π-A-structured organic dyes, coded as SGT-138, SGT-150, and SGT-151, with the expansion of π-conjugation in the π-bridge and acceptor parts have been developed to adjust HOMO/LUMO levels and to expand the light absorption range of organic dyes. Referring to the SGT-137 dye, the π-bridge group was extended from the 4-hexyl-4H-thieno[3,2-b]indole (TI) to the 9-hexyl-9H-thieno[2',3':4,5]thieno[3,2-b]indole (TII), and the acceptor group was extended from (E)-3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic acid (BTCA) to (E)-3-(4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)phenyl)-2-cyanoacrylic acid (BTECA), where TII was introduced as a π-bridging unit for the first time. It was determined that both extensions are promising strategies to enhance the light-harvesting ability. They present several features, such as (i) efficiently intensifying the extinction coefficient and expanding the absorption bands; (ii) exhibiting enhanced intramolecular charge transfer in comparison with the SGT-137; and (iii) being favorable to photoelectric current generation of dye-sensitized solar cells (DSSCs) with cobalt electrolytes. In particular, the π-spacer extension from TI to TII was useful for modulating the HOMO energy levels, while the acceptor extension from BTCA to BTECA was useful for modulating the LUMO energy levels. These phenomena could be explained with the aid of density functional theory calculations. Finally, the DSSCs based on new SGT-dyes with an HC-A1 co-adsorbent presented good power conversion efficiencies as high as 11.23, 11.30, 11.05, and 10.80% for SGT-137, SGT-138, SGT-150, and SGT-151, respectively. Furthermore, it was determined that the use of the bulky co-adsorbent, HC-A1, can effectively suppress the structural relaxation of dyes in the excited state, thereby enhancing the charge injection rate of SGT-dyes. The observations in time-resolved photoluminescence were indeed consistent with the variation in the PCE, quantitatively.

An optimal molecule-matching co-sensitization system for the improvement of photovoltaic performances of DSSCs

Three biphenyl co-sensitizers (4OBA, 8OBA and 12OBA) with different terminal oxyalkyl chains were synthesized and co-sensitized respectively with the main dye (NP-1) in co-sensitized solar cells (co-DSSCs). The effects of the terminal oxyalkyl chains on the photophysical, electrochemical and photovoltaic properties of the co-DSSCs were systematically investigated. The optimal molecular matching relationship between the co-sensitizers and the main dye was obtained through density functional theory (DFT) calculations. Consequently, 4OBA has the most appropriate three-dimensional (3D) molecular structure, which could not only fill the gap between the large-size dyes but also plays a partial shielding role, inhibiting dye aggregation and electron recombination, therefore yielding the highest power conversion efficiency (PCE) for the co-DSSCs with NP-1@4OBA. This study suggests that adjusting the terminal oxyalkyl chains of the co-sensitizers can be used to enhance the intramolecular charge transfer efficiency and inhibit electron recombination, ultimately improving the photovoltaic performances of the co-DSSCs.

Efficient Solar Cells Sensitized by Organic Concerted Companion Dyes Suitable for Indoor Lamps

In this work, organic concerted companion (CC) dyes CCOD-1 and CCOD-2 were constructed by covalently linking two organic dye units with complementary absorption spectra. Both CC dyes exhibited intense absorption from 300 to 650 nm with the band edges extended to 700 nm. These CC dyes were used to fabricate dye-sensitized solar cells (DSSCs), and the photovoltaic performance was investigated using different light sources. CCOD-2 possessed bulkier outer shelter than CCOD-1 owing to the longer carbon chains (C₁₂ ) at the donor moiety, and thus it had stronger anti-aggregation and anti-charge-recombination ability. Under simulated sunlight (AM1.5G), CCOD-2 exhibited enhanced photovoltaic behavior with an open-circuit voltage (V_OC ) of 759 mV, short-circuit current density (J_SC ) of 19.23 mA ⋅ cm^-2 , and power conversion efficiency (PCE) of 10.4 %, respectively. Notably, under the illumination of the indoor T5 fluorescent lamp (2500 lux), CCOD-2 afforded an enhanced PCE of 28.0 % with remarkable V_OC and J_SC of 692 mV and 0.424 mA cm^-2 , respectively. Notably, the PCE achieved for CCOD-2 outperformed those of the reference sensitizer N719 and our previously reported CC dyes XW61 and XW70-C8 under the same indoor lamp conditions. In summary, the novel organic CC dyes developed in this work were demonstrated to be promising for fabricating DSSCs to efficiently harvest the energy of indoor lamps.

Peptide Materials in Dye Sensitized Solar Cells

In September 2015, the ONU approved the Global Agenda for Sustainable Development, by which all countries of the world are mobilized to adopt a set of goals to be achieved by 2030. Within these goals, the aim of having a responsible production and consumption, as well as taking climate action, made is necessary to design new eco-friendly materials. Another important UN goal is the possibility for all the countries in the world to access affordable energy. The most promising and renewable energy source is solar energy. Current solar cells use non-biodegradable substrates, which generally contribute to environmental pollution at the end of their life cycles. Therefore, the production of green and biodegradable electronic devices is a great challenge, prompted by the need to find sustainable alternatives to the current materials, particularly in the field of dye-sensitized solar cells. Within the green alternatives, biopolymers extracted from biomass, such as polysaccharides and proteins, represent the most promising materials in view of a circular economy perspective. In particular, peptides, due to their stability, good self-assembly properties, and ease of functionalization, may be good candidates for the creation of dye sensitized solar cell (DSSC) technology. This work shows an overview of the use of peptides in DSSC. Peptides, due to their unique self-assembling properties, have been used both as dyes (mimicking natural photosynthesis) and as templating materials for TiO2 morphology. We are just at the beginning of the exploitation of these promising biomolecules, and a great deal of work remains to be done.

Accurate Determination of Adsorption-Energy Differences of Metalloporphyrins on Rutile TiO2(110) 1 × 1

Understanding the adsorption of organic molecules on surfaces is of essential importance for many applications. Adsorption energies are typically measured using temperature-programmed desorption. However, for large organic molecules, often only desorption of the multilayers is possible, while the bottom monolayer in direct contact to the surface cannot be desorbed without decomposition. Nevertheless, the adsorption energies of these directly adsorbed molecules are the ones of the most interest. We use a layer-exchange process investigated with X-ray photoelectron spectroscopy to compare the relative adsorption energies of several metalated tetraphenylporphyrins on rutile TiO₂(110) 1 × 1. We deposit a mixture of two different molecules, one on top of the other, and slowly anneal above their multilayer desorption temperature. During the slow heating, the molecules begin to diffuse between the layers and the molecules with the stronger interaction with the surface displace the weaker-interacting molecules from the surface and push them into the multilayer. The multilayers eventually desorb, leaving behind a monolayer of strongly interacting molecules. From the ratio of the two different porphyrin molecules in the residual monolayer and the desorbed multilayer, we can calculate the equilibrium constant of the layer-exchange process and thereby the difference in adsorption energy between the two different porphyrin molecules.

Efficient Dye-Sensitized Solar Cells Based on a New Class of Doubly Concerted Companion Dyes

To develop efficient dye-sensitized solar cells (DSSCs), concerted companion (CC) dyes XW60-XW63 constructed from the covalent linkage of a strapped porphyrin dye unit and an organic dye unit have been reported to exhibit panchromatic absorption and excellent photovoltaic performance. However, these CC dyes only afforded moderate VOC values of ca. 763 mV, demonstrating relatively weak antiaggregation ability, which remains an obstacle for further enhancing the photovoltaic behavior. To address this problem, we herein develop porphyrin dyes XW77-XW80 with the macrocycles wrapped with alkoxy chains of various lengths (OC6H13-OC22H45) and the corresponding CC dyes XW81-XW84 containing these porphyrin dye units. Interestingly, the new CC dyes XW81-XW83 exhibit increasing VOC from 745 to 784 mV with the chain lengths extended from C6 to C18, and a lowered VOC of 762 mV was obtained for XW84 when the chain length was further extended to C22. As a result, XW83 afforded the highest PCE of 12.2%, which is, to the best of our knowledge, the record efficiency for the iodine electrolyte-based solar cells sensitized with a single dye. These results can be rationalized by the so-called doubly concerted companion (DCC) effects, that is, the two subdye units exhibit not only complementary absorption but also concerted antiaggregation with the long wrapping chains on the porphyrins unit simultaneously protecting the porphyrin macrocycle and the neighboring organic subdye unit, thus affording panchromatic absorption and strong antiaggregation and anticharge-recombination ability. These results provide a new approach for constructing a class of DCC dyes to achieve high-performance DSSCs without using any antiaggregating coadsorbent or absorption-enhancing cosensitizer.

Synthesis and Spectral Properties of Aggregation-Induced Emission-Active Push-Pull Chromophores Based On Isoindole Scaffolds

A new class of tailor-made push-pull isoindole fluorophores has been synthesized through the combination of Suzuki coupling and Knoevenagel reactions. The efficient synthetic strategy rendered the isoindole scaffold as the π-bridge and the isolation spacer and provided dyes bearing various types of electron donors and electron acceptors for manipulating their energy gaps and tuning their absorptions and emissions. Most of the N-alkylated isoindole dyes showed aggregation-induced emission behaviors suitable for bioimaging and nice solid-state emission with maxima up to 851 nm.

Synthesis, Characterization, DFT and Photocatalytic Studies of a New Pyrazine Cadmium(II) Tetrakis(4-methoxy-phenyl)-porphyrin Compound

This study describes the synthesis, theoretical investigations, and photocatalytic degradational properties of a new (pyrazine)(meso-tetrakis(4-tert-methoxyphenyl)-porphyrinato)-cadmium (II) ([Cd(TMPP)-Pyz]) complex (1). The new penta-coordinated Cd^II porphyrin complex (1) was characterized by various spectroscopic techniques, including FT-IR, NMR, UV-visible absorption, fluorescence emission, and singlet oxygen, while its molecular structure was studied using single crystal X-ray diffraction. The UV–Vis spectroscopic study highlighted the redshift of the absorption bands after the insertion of the Cd(II) metal ion into the TMPP ring. The co-coordination of the pyrazine axial ligand enhanced this effect. A fluorescence emission spectroscopic study showed a significant blueshift in the Q bands, accompanied by a decrease in the fluorescence emission intensity and quantum yields of Φ_f = 0.084, Φ_f = 0.06 and Φ_f = 0.03 for H₂-TMPP free-base porphyrin, [Cd(TMPP)] and [Cd(TMPP)(Pyz)] (1) respectively. Singlet oxygen revealed that the H₂-TMPP porphyrin produced the most efficient singlet oxygen quantum yield of (Φ_Δ = 0.73) compared to [CdTMPP] (Φ_Δ = 0.57) and [Cd(TMPP)(Pyz)] (1) (Φ_Δ = 0.13). In the crystal lattice, the [Cd(TMPP)Pyz] was stabilized through non-covalent intermolecular interactions (NCI), such as the hydrogen bonds C-H···N and C-H···Cg. Additionally, crystal explorer software was then utilized to measure the quantitative analysis of the intermolecular interactions in the unit cell of the crystal structure and established that the C-H···π interaction dominated. The Natural bond orbital (NBO) analysis revealed that each molecule is stabilized by hyperconjugation and charge delocalization. As a photocatalyst, the coordination complex 1 showed excellent photocatalytic activity toward the degradation of Levafix Blue CA reactive dye (i.e., dye photo-degradation of 80%).

Polyimide-Based Covalent Organic Framework as a Photocurrent Enhancer for Efficient Dye-Sensitized Solar Cells

Covalent organic frameworks (COFs) are of great interest in the energy and optoelectronic fields due to their high porosity, superior thermal stability, and highly ordered conjugated architecture, which are beneficial for charge migration, charge separation, and light harvesting. In this study, polyimide COFs (PI-COFs) are synthesized through the condensation reaction of pyromellitic dianhydride (PMDA) with tris(4-aminophenyl) amine (TAPA) and then doped in the TiO₂ photoelectrode of a dye-sensitized solar cell (DSSC) to co-work with N719 dye to explore their functionality. As a benchmark, the pristine DSSC without the doping of PI-COFs exhibits a power conversion efficiency of 9.05% under simulated one sun illumination. The doping of 0.04 wt % PI-COFs contributes an enhanced short-circuit current density (J_SC) from 17.43 to 19.03 mA/cm², and therefore, the cell efficiency is enhanced to 9.93%. The enhancement of J_SC is attributed to the bifunctionality of PI-COFs, which enhances the charge transfer/injection and suppresses the charge recombination through the host (PI-COF)-guest (N719 dye) interaction. In addition, the PI-COFs also function as a cosensitizer and contribute a small quantity of photoinduced electrons upon sunlight illumination. Surface modification of oxygen plasma improves the hydrophilicity of PI-COF particles and reinforces the heterogeneous linkage between PI-COF and TiO₂ nanoparticles, giving rise to more efficient charge injection. As a result, the champion cell exhibits a high power conversion efficiency of 10.46% with an enhanced J_SC of 19.43 mA/cm². This methodology of increasing solar efficiency by modification of the photoelectrode with the doping of PI-COFs in the TiO₂ nanoparticles is promising in the development of DSSCs.

Dye Sensitization Offers a Brighter Afterglow Nanoparticle Future for in vivo Recharged Luminescent Imaging

While concerns about improving recharged afterglow intensity in vivo still motivate further exploration, afterglow nanoparticles (AGNP) offer unique optical merit for autofluorescence-free biological imaging. Apart from efforts enhancing the afterglow emission properties of AGNP, improving afterglow excitation response to visible or near infrared light is important but has lacked success. Dye sensitization has been used to improve the optical response of photovoltaic nanomaterials and to enhance upconversion luminescence efficiency. This concept has recently been expanded and applied to AGNPs. As a new multifunctional nanoprobe, such dye-sensitized AGNP takes advantage of both high spatial resolution fluorescence imaging and sensitive afterglow imaging. This Concept introduces the background, the concept, mechanism, and related imaging application, as well as reviewing existing challenges and proposing future developmental directions for the dye-sensitized AGNPs.

An unprecedented fully reduced {MoV 60} polyoxometalate: from an all-inorganic molecular light-absorber model to improved photoelectronic performance

Fully reduced polyoxometalates are predicted to give rise to a broad and strong absorption spectrum, suitable energy levels, and unparalleled electronic and optical properties. However, they are not available to date. Here, an unprecedented fully reduced polyoxomolybdate cluster, namely Na8[MoV 60O140(OH)28]·19H2O {MoV 60}, was successfully designed and obtained under hydrothermal conditions, which is rare and is the largest fully reduced polyoxometalate reported so far. The MoV 60 molecule describes one Keggin {ε-Mo12} encapsulated in an unprecedented {Mo24} cage, giving rise to a double truncated tetrahedron quasi-nesting architecture, which is further face-capped by another four {Mo6} tripods. Its crystalline stability in air, solvent tolerance, and photosensitivity were all shown. As a cheap and robust molecular light-absorber model possessing wide light absorption, MoV 60 was applied to build a co-sensitized solar cell photoelectronic device along with N719 dyes and the optimal power conversion efficiency was 28% higher than that of single-dye sensitization. These results show that MoV 60 polyoxometalate could serve as an ideal model for the design and synthesis of all-inorganic molecular light-absorbers for other light-driven processes in the future.

Phenothiazine-Embedded Hexaphyrins

Unprecedented nonaromatic stable phenothiazine-embedded porphyrinoids were synthesized by incorporating phenothiazine subunits into the hexaphyrin framework. The crystal structure revealed that the macrocycle adopted a twisted conformation wherein the phenothiazine units maintained their planarity, which was an impediment in π-delocalization throughout the macrocyclic core. The macrocycles exhibited distinct absorption bands in the visible-near-infrared region, and electrochemical studies indicated their electron-rich nature. Theoretical studies were consistent with the experimental observations.

Synthesis, photophysical, electrochemical, and DFT examinations of two new organic dye molecules based on phenothiazine and dibenzofuran

New dyes were developed and produced utilizing distinct electron donors (phenothiazine and dibenzofuran), a π-spacer, and an electron acceptor of cyanoacetohydrazide, and their structures were studied using FT-IR and NMR spectroscopy. Following the synthesis of dye molecules, the photophysical and photovoltaic characteristics were investigated using experimental and theoretical methods. The photosensitizers have been exposed to electrochemical and optical property experiments in order to study their absorption performance and also molecular orbital energies. The monochromatic optical conversion efficiency of (Z)-N-((5-(10H-phenothiazin-2-yl)furan-2-yl)methylene)-2-cyanoacetohydrazide (PFCH) was found higher than that of (Z)-2-cyano-N'-((5-(dibenzo[b,d]furan-4-yl)furan-2-yl)methylene)acetohydrazide (BFCH), with IPCEs of 58 and 64% for BFCH and PFCH, respectively. According to the photosensitizer molecular energy level diagram, the studied dye molecules have strong thermodynamically advantageous ground and excited-state oxidation potentials for electron injection into the conduction band of titanium oxide. It was observed that the ability to attract electrons correlated favorably with molecular orbital energy. While density functional theory calculations were used to examine molecule geometries, vertical electronic excitations, and frontier molecular orbitals, experimental and computed results were consistent. Natural bond orbital and nonlinear optical properties were also calculated and discussed.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.

Effect of Extending the Conjugation of Dye Molecules on the Efficiency and Stability of Dye-Sensitized Solar Cells

We designed and synthesized two organic dyes (A6 and A10) for dye-sensitized solar cells (DSSCs) by extending the molecular conjugation strategy. The sensitizer A10 was constructed by inserting ethene into our previously reported sensitizer AZ6. The sensitizer A6 was obtained by further substituting the hydrogen of ethene with another donor (D) and π-bridge-acceptor (π-A) segment. The UV-vis spectra and J-V curves showed that the dyes A10 and A6 could effectively facilitate the light-harvesting and photocurrent densities with respect to AZ6. Consequently, the A10-based DSSC achieved an enhanced efficiency (8.54%) with a high photocurrent (18.81 mA cm^-2). Desorption experiments of dyes adsorbed on TiO₂ showed that compared with the monoanchoring dyes AZ6 and A10, the dianchoring configuration effectively strengthened the affinity of dye A6 with the photoanode, making it more difficult to leach from the photoanode. The A6-based DSSC shows outstanding stability, and its overall efficiency could remain 98.0% of its initial value after 3000 h of aging time, exceeding that of its monoanalogue AZ6 (remained 78.3% after 3000 h).

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.

Optimizing the Cosensitization Effect of SQ02 Dye on BP-2 Dye-Sensitized Solar Cells: A Computational Quantum Chemical Study

Cosensitization of the semiconducting electrode in dye-sensitized solar cells (DSCs), with two or more light-harvesting dyes, is a chemical fabrication method that aims to achieve a panchromatic absorption spectrum emulating that of the solar emission spectrum. In this paper, SQ02 and BP-2 cosensitizers have been investigated, as isolated monomers/dimer and adsorbed monomers/dimer on the TiO₂ (101) anatase surface, by employing density functional theory (DFT) and time-dependent DFT calculations. Computed results showed that the dominant electron injection pathway is direct injection from each dye into the conduction band of TiO₂. The almost complete spectral overlap between the simulated absorption spectrum of BP-2 and fluorescence emissions of SQ02 implies that excitation energy transfer occurs between cosensitizers via the trivial reabsorption mechanism. However, the results showed very limited unidirectional intermolecular charge transfer (CT) from SQ02 dye to BP-2 dye (0.04 |e^-|). Therefore, this study also presents a stepwise molecular engineering of BP-2 dye, aiming at optimizing the cosensitization functionality. First, 14 redesigned dye candidates are reported to identify dyes with photophysical properties matching the requirements for efficient DSCs. Second, the four most promising dyes are shortlisted for testing as cosensitizers with the SQ02 dye. The molecular design factors of cosensitization that need validation are chemical compatibility, availability of CT between cosensitizers, and complementarity of the absorption spectra. This screening suggests the judicious choice of the modeled difluorenyl amine donor-based dye (BP-D4) as a very promising cosensitizer. In particular, the SQ02/BP-D4 dimer showed 10 times larger (0.53 |e^-|) unidirectional CT than that of SQ02/BP-2 dimer, in addition to the maximum increased electron population of acceptor moieties upon photoexcitation.

Syntheses of thiophene appended N-confused phlorin isomers

A doubly confused thiapentapyrrane NSP-5 was synthesized by acid-catalysed condensation. Subsequent oxidation with DDQ did not afford the expected thiasapphyrin-like product. Instead, two tetrapyrrolic macrocycles, i.e. neo-N-confused phlorin (1) and N-confused phlorin-II (2) were obtained in the yields of 14% and 18%, respectively. The compounds were characterized by NMR, HRMS, and X-ray diffraction analyses. Single crystal structures clearly reveal that the thienyl units are not embedded into the macrocycles, but appended as meso-substituents, and the C[Formula: see text]-N and C[Formula: see text]-C[Formula: see text] cyclization modes can be clearly revealed by the crystal structures of 1 and 2, respectively. The observation that the thienyl unit is not involved in oxidative cyclization may be related to the relatively low reactivity of the thiophene moiety compared with the more electron-rich pyrrole unit. These results indicate that oxidative cyclization of linear thiaoligopyrranes containing terminal thiophene units may be developed as an effective approach for synthesizing nonconjugated macrocycles like phlorin analogues.