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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. [ABSTRACT FROM AUTHOR]

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 (VOC) of 759 mV, short‐circuit current density (JSC) 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 VOC and JSC 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. [ABSTRACT FROM AUTHOR]

To develop cosensitizers for fabricating dye-sensitized solar cells (DSSCs) based on porphyrin dyes, C2 and C3 have been synthesized using a diphenylamine donor, an anthracene based π-spacer and a benzoic acid acceptor on the basis of our previously reported cosensitizer C1. Thus, two hexyloxy chains have been introduced in the diphenylamine donor to synthesize C2 with the purpose of extending the absorption wavelength range and suppressing the charge recombination, and C3 has been synthesized by introducing two bulky 2,4-bis(hexyloxy)phenyl groups in the diphenylamine donor to effectively suppress dye aggregation and charge recombination between the injected electrons and the electrolyte. On this basis, DSSCs have been fabricated by using C1–C3 based on the cobalt electrolyte. As expected, an obviously higher Jsc of 13.03 mA cm−2 has been obtained for C2 relative to that of 11.92 mA cm−2 obtained for C1. As a result, C2 shows a slightly improved efficiency of 7.59%. On the other hand, the molecular structure of C3 has been further optimized with two bulky dihexyloxyphenyl units, and thus the suppressed interfacial back electron transfer improves the Jsc to 13.23 mA cm−2 and the superior anti-aggregation ability enhances the Voc to 857 mV. Finally, the highest PCE value of 8.95% is achieved for C3. On this basis, cosensitization with XW66 affords remarkable efficiencies of 9.06%, 9.89% and 10.22% for C1–C3, respectively. These results provide an effective approach for developing efficient cosensitizers for porphyrins by introducing suitable substituents into the donor unit. [ABSTRACT FROM AUTHOR]

A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face‐to‐face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells (DSSCs) have attracted intensive attention in developing photovoltaic devices for employing solar energy. For developing panchromatic and efficient porphyrin sensitizers, it has been demonstrated to be an effective approach to introduce an electron-withdrawing benzothiadiazole unit as an extra electron acceptor. In contrast, the structurally similar benzotriazole moiety remains relatively unknown in this respect. In this work, we have synthesized a novel porphyrin dye containing an extra electron acceptor of benzotriazole. Photophysical and electrochemical investigations revealed red-shifted absorption and a narrower band gap induced by the benzotriazole unit. Thus, a reasonable efficiency of 8.39% has been achieved with a J sc of 17.00 mA cm −2 and a V oc of 712 mV. On this basis, to investigate the effect of the dihedral angle between the benzotriazole and the adjacent phenylene ring, one or two methyl groups were attached to the ortho -positions of the phenylene ring. As a result, the enlarged torsion angles induce poor electronic coupling between the LUMO of the dyes and TiO 2 , resulting in lower efficiencies of 6.61% and 3.62%, respectively. With the purpose to further improve the efficiencies, coadsorption and cosensitization approaches were employed. And the efficiencies have been successfully elevated to 9.32%, 8.49% and 7.34%, respectively. These results demonstrate the effectiveness of incorporating an auxiliary benzotriazole acceptor into porphyrin dyes on achieving extended light-harvesting wavelength ranges and illustrate the importance of avoiding severe torsion within the acceptor part of the porphyrin dyes. In contrast to the commonly used cosensitizers with absorption peaks lying in the absorption valley between the Soret band and the Q bands of porphyrin dyes (500–600 nm), the utilization of an organic dye with broad absorption in this work has been demonstrated to be effective for improving the efficiencies despite the fact that its absorption peak at 450 nm largely overlaps with the Soret band of the porphyrin dyes. These results provide an alternative approach for developing cosensitizers for porphyrin dyes. [ABSTRACT FROM AUTHOR]

With the purpose to develop efficient dye-sensitized solar cells (DSSCs), a series of push-pull porphyrin dyes have been designed and optimized by introducing additional electron-donating diphenylamino and electron-withdrawing benzothiadiazole moieties. Electrochemical, photophysical and photovoltaic investigations indicate that the introduction of additional donors and acceptors can effectively extend the absorption spectra, resulting in better sunlight harvesting. However, the HOMO levels of the dyes are elevated by the additional donors, resulting in decreased driving forces for dye regeneration and decreased cell efficiencies. Upon coadsorption with 5 mM chenodeoxycholic acid (CDCA), the cell efficiencies can be elevated from 1.37% - 5.01% to 1.70% - 6.97%. Furthermore, based on the subtle absorption characteristics of the porphyrin dyes, we delicately designed a cocktail co-sensitization strategy using the solutions containing two of the porphyrin dyes as well as CDCA. Finally, a high photovoltaic efficiency of 8.6% was successfully achieved at an optimized molar ratio of 10:1 for the two porphyrin dyes. [ABSTRACT FROM AUTHOR]

Four alkoxy-wrapped push-pull porphyrin dyes containing the phenothiazine derived donor and the ethynylbenzoic acid acceptor have been designed, synthesized and used as sensitizers for fabricating efficient dye-sensitized solar cells (DSSCs). Branched or linear alkoxy chains were introduced to the ortho -positions of the meso- phenyl moieties to suppress the dye aggregation and charge recombination. The effect of alkoxy chains were investigated in the absence and presence of an additional electron-withdrawing benzothiadiazole unit. In the former cases, almost identical photovoltaic efficiencies of ∼8.3% were achieved for both the branched and the linear alkoxy chains, while in the latter cases, the planar benzothiadiazole unit induces serious dye aggregation and charge recombination, resulting in lower efficiencies of 6.46% and 7.50% for the linear and branched chains, respectively, even though broader absorption was achieved. The relatively higher efficiency achieved for the dyes with branched chains may be related to the better effect of suppressing the dye aggregation and charge recombination. Furthermore, the coadsorption approach was employed, and a highest efficiency of 9.62% was achieved for the dye that features branched chains and the benzothiadiazole unit. These results compose a novel approach for developing efficient DSSCs by combining the coadsorbent with a porphyrin dye containing both the additional benzothiadiazole acceptor and branched alkoxy chains. [ABSTRACT FROM AUTHOR]

Abstract: Four novel naphthalimide-based dyes (D-1, D-2, D-3 and D-4) were synthesized and utilized as sensitizers in dye-sensitized solar cells (DSCs), in which the triphenylamine (TPA) or indoline groups, naphthalimide unit and carboxylic group were functionalized as electron donor, acceptor and anchoring group, respectively. The naphthalimide unit was employed as the π-conjugation ring and electron acceptor for effectively realizing intramolecular charge separation in the oxidized states. In the series of dyes, the LUMO orbital is delocalized mainly on naphthalimide moieties, especially on the carbonyl group. Consequently, the LUMO electrons are isolated from the carboxyl anchoring group (-CH2CO2H) due to the presence of the methylene group, which could suppress the electron injection efficiency from the excited dyes to the TiO2 conduction band, thus leading to the inferior efficiencies of 1.10, 1.18, 2.27 and 2.70%, respectively, even though they exhibit broad spectral response and high extinction coefficients. [Copyright &y& Elsevier]

To fabricate efficient dye-sensitized solar cells (DSSCs), three porphyrin dyes XW65 − XW67 have been designed and synthesized using a bulky triphenylamine donor. Based on our previously reported dyes with a carbazole donor, a bulky triphenylamine unit was employed as the donor to synthesize XW65 with the aim to enhance the electron donating ability and suppress dye aggregation. As a result, XW65 shows enhanced photocurrent density (J sc) and open circuit voltage (V oc), affording a high efficiency of 9.02%. On this basis, XW66 was synthesized with a methyl group introduced into the carboxyphenyl acceptor to further suppress dye aggregation and improve the V oc , achieving an enhanced efficiency of 9.23% with improved V oc of 849 mV and J sc of 14.87 mA cm−2, which can be ascribed to the further suppressed dye aggregation and enhanced adsorption amount on the TiO 2 film induced by the additional methyl group. To further improve the J sc , a benzothiadiazole (BTD) unit has been introduced as the auxiliary acceptor to afford XW67 , which exhibits a strikingly red-shifted monochromatic photon-to-electron conversion efficiency (IPCE) onset wavelength of 830 nm, obtaining the highest J sc value of 15.83 mA cm−2 among the three dyes. Consequently, despite the sacrifice of V oc caused by the severe dye aggregation associated the extended conjugation framework, XW67 exhibits the highest efficiency of 9.43%. On this basis, cosensitization with WS-5 afforded elevated efficiencies of 10.07%, 10.38% and 10.13% for XW65 − XW67 , respectively, owing to the simultaneously enhanced J sc and V oc. These results indicate that it is effective to develop efficient DSSCs based on cosensitization of optimized porphyrin dyes containing a bulky triphenylamine donor, a methyl group on the carboxyphenyl acceptor, and an auxiliary electron acceptor. Image 1 • A strikingly red-shifted monochromatic incident photon to current conversion efficiency (IPCE) onset wavelength of 830 nm. • Better suppression of dye-aggregation and by bulky substituents on the donor and a methyl group on the carboxyphenyl acceptor. • The absorption drawbacks of the porphyrin dyes compensated by a broad band of the cosensitizer. • An efficiency 10.38% achieved with synergetically enhanced V oc and J sc. [ABSTRACT FROM AUTHOR]

Three porphyrin sensitizers XW54 – XW56 containing a carbazole donor have been designed and synthesized by introducing a benzothiadiazole (BTD) unit as the auxiliary electron acceptor to extend the absorption spectra and/or bulky dihexyloxyphenyl groups into the carbazole unit to suppress dye aggregation and improve the photovoltage (V oc). The BTD unit incorporated in XW54 obviously broadens and red-shifts the absorption threshold to ca. 700 nm, as compared with that of 650 nm observed for XW1. Thus, XW54 exhibits a much broader monochromatic photon-to-electron conversion efficiency (IPCE) spectrum with an extremely red-shifted onset wavelength of 780 nm, resulting in a photocurrent density (J sc) of 11.60 mA cm−2, higher than that of XW1. Unfortunately, the V oc value was decreased owing to the more severe dye aggregation caused by the large conjugation framework induced by the presence of the BTD unit. As a result, XW54 shows an efficiency of 6.26%, slightly higher than that of 6.11% obtained for XW1. On the other hand, with the bulky dihexyloxyphenyl donor groups introduced to XW55 , a highest V oc of 860 mV was achieved, which can be ascribed to the efficient prevention of charge recombination and suppression of dye aggregation. Thus, XW55 -based cells exhibit an improved efficiency of 6.60%. On the basis of XW54 and XW55 , two bulky dihexyloxyphenyl groups and a BTD unit were simultaneously introduced to XW56 , affording a highest efficiency of 7.03%, with the J sc and V oc values of 12.5 mA cm−2 and 785 mV, respectively. These results compose a novel approach for developing efficient dye-sensitized solar cells (DSSCs) by simultaneously introducing bulky dihexyloxyphenyl groups and a benzothiadiazole unit, which may synergistically broaden the absorption spectra and suppress the dye aggregation, resulting in improved photocurrent and photovoltage. Image 1 • Absorption of porphyrins extended by introducing an auxiliary benzothiadiazole acceptor. • Better suppression of dye-aggregation and charge recombination by bulky substituents. • With synergetically enhanced V oc and J sc , an improved efficiency 7.03% was achieved. [ABSTRACT FROM AUTHOR]