Iodide/triiodide redox shuttle-based additives for high-performance perovskite solar cells by simultaneously passivating the cation and anion defects

Halide perovskite solar cells (PSCs) have received remarkably increasing interests due to their facile fabrication procedures, use of cost-effective raw materials, and high power conversion efficiencies (PCEs) during the past 10 years. Nevertheless, the state-of-the-art organic-inorganic PSCs suffer from high defect concentration and inferior humid/thermal stability, significantly restricting the widespread applications of PSCs. More specifically, point defects including metallic lead (Pb⁰) and halide iodine (I⁰) are easily generated in Pb/I-based PSCs during fabrication processes and operational conditions due to the inferior interaction between the anions and cations in halide perovskites and promote detrimental carrier recombination and ion migration, leading to inferior PCEs and durability of the PSCs. Herein, to tackle the above-mentioned issues, iodide/triiodide (I^-/I₃^-) redox shuttles as a new additive were introduced to simultaneously passivate the cation and anion defects of methylammonium lead iodide (MAPbI₃)-based PSCs. In particular, I^-/I₃^- redox shuttles play a vital role in regenerating the cation (Pb⁰) and anion (I⁰) defects through the redox cycles of Pb⁰/Pb²⁺ and I⁰/I^-. Consequently, the cell with an optimized amount of I^-/I₃^- additive generated a superior PCE of 20.4%, which was 12% higher than the pristine device (18.2%). Furthermore, the introduction of the I^-/I₃^- additive remarkably improved the humid and thermal stability of MAPbI₃-based PSCs. This work manifests the importance of the design of redox shuttle-based additives to boost the efficiency and durability of organic-inorganic PSCs.

Non-Symmetrical Sterically Challenged Phenanthroline Ligands and Their Homoleptic Copper(I) Complexes with Improved Excited-State Properties

A strategy is presented to improve the excited state reactivity of homoleptic copper-bis(diimine) complexes CuL₂ ⁺ by increasing the steric bulk around Cu^I whereas preserving their stability. Substituting the phenanthroline at the 2-position by a phenyl group allows the implementation of stabilizing intramolecular π stacking within the copper complex, whereas tethering a branched alkyl chain at the 9-position provides enough steric bulk to rise the excited state energy E⁰⁰ . Two novel complexes are studied and compared to symmetrical models. The impact of breaking the symmetry of phenanthroline ligands on the photophysical properties of the complexes is analyzed and rationalized thanks to a combined theoretical and experimental study. The importance of fine-tuning the steric bulk of the N-N chelate in order to stabilize the coordination sphere is demonstrated. Importantly, the excited state reactivity of the newly developed complexes is improved as demonstrated in the frame of a reductive quenching step, evidencing the relevance of our strategy.

Ferrocene Derivatives Functionalized with Donor/Acceptor (Hetero)Aromatic Substituents: Tuning of Redox Properties

A series of functionalized ferrocene derivatives carrying electron-donor and electron-withdrawing (hetero)aromatic substituents has been designed as potential alternative electrolyte redox couples for dye-sensitized solar cells (DSSC). The compounds have been synthesized and fully characterized in their optical and electrochemical properties. A general synthetic approach that implies the use of a microwave assisted Suzuki coupling has been developed to access a significative number of compounds. The presence of different electron-rich and electron-poor substituents provided fine tuning of optical properties and energy levels. HOMO and LUMO energy values showed that the substitution of one or two cyclopentadienyl rings of ferrocene can be successfully exploited to increase the maximum attainable voltage from a standard DSSC device using TiO2 as a semiconductor, opening the way to highly efficient, non-toxic, and cheap redox shuttles to be employed in solar energy technologies.

Thiazolocatechol: Electron-Withdrawing Catechol Anchoring Group for Dye-Sensitized Solar Cells

Anchoring groups adopting a five-membered bidentate chelating are attractive to realize high power conversion efficiency (η) and long-term durability in dye-sensitized solar cells (DSSCs). In this regard, we chose catechol as an anchoring group that can adopt the chelating. However, the DSSCs with catechol-based sensitizers have never exceeded an η-value of 2 %. These poor photovoltaic performances may be associated with the electron-donating ability of the hydroxy groups in catechol. Considering these, we envisioned that fusing an electron-withdrawing thiazole moiety with a catechol anchoring group would improve its photovoltaic performance. Herein, we report a push-pull porphyrin sensitizer ZnPTC with a thiazolocatechol anchoring group. The DSSC with ZnPTC exhibited η=4.87 %. This value is the highest ever reported for catechol-anchor based DSSCs. Meanwhile, the long-term cell durability was not improved, although the robust anchoring properties were attained under harsh conditions.

Renaissance of Fused Porphyrins: Substituted Methylene-Bridged Thiophene-Fused Strategy for High-Performance Dye-Sensitized Solar Cells

Over the last decades, porphyrin sensitizers have made a remarkable contribution to performance improvement in dye-sensitized solar cells (DSSCs). In particular, versatile push-pull-type porphyrin sensitizers have achieved power conversion efficiencies (η) over 10% as a result of their improved light-harvesting abilities. Meanwhile, aromatic ring fusion to a porphyrin core is an attractive option for highly efficient DSSCs because of its expanded π-conjugation and resultant red-shifted absorption. Nevertheless, aromatic-fused porphyrin sensitizers have suffered rather low cell performances due to their mismatch of HOMO-LUMO levels, high aggregation tendency, and short lifetime of the excited states. Bearing these in mind, we envisioned that the fusion of substituted methylene-bridged small aromatic ring to a porphyrin core would overcome these drawbacks, boosting the cell performance. Herein, we report a series of substituted methylene-bridged thiophene-fused porphyrins, AfZnP, DfZnP, and DfZnP- iPr. After optimization, DSSC with the donor-side thiophene-fused DfZnP- iPr achieved an η-value of 10.1%, which is comparable to that of DSSC with GY50 (10.0%), a representative high-performance push-pull-type porphyrin sensitizer. More importantly, cosensitization of DfZnP- iPr with a complementary sensitizer LEG4 further led to an η-value of 10.7%, which is the highest value ever reported for DSSCs with fused porphyrin sensitizers. Therefore, our strategy will reboot the exploration of aromatic-fused porphyrin sensitizers for high-performance DSSCs.

Synthesis, structure, and photophysical and electrochemical properties of Ru(ii) complexes of arylene-vinylene terpyridyl conjugates

A series of arylene-vinylene π-conjugated terpyridyl ruthenium(ii) complexes, [Ru(PPh3)2Cl(tpy-C6H4-CH[double bond, length as m-dash]CH-Ar)][PF6] (1-4; tpy = 2,2':6',2''-terpyridyl, where Ar = phenyl, tolyl, 1-naphthyl and 9-anthracenyl as substituents at the 4' position of tpy), have been synthesized and characterized by multinuclear NMR, IR, HRMS and single crystal X-ray crystallography. The influence of the electronic nature of arylene groups on their photophysical and electrochemical properties has been investigated to understand the electronic interaction between the metal-organic redox centers. Furthermore, a σ-donor phenylacetylide group has been incorporated to accomplish [Ph-C[triple bond, length as m-dash]C-Ru(PPh3)2(tpy-C6H4-CH[double bond, length as m-dash]CH-Ar)][PF6] (5-8) complexes by the substitution of a coordinated chloride ligand and to investigate the change in their redox and photophysical properties. DFT studies have been performed to gain an insight into their electronic properties by determining the HOMO-LUMO energy levels and frontier molecular orbitals of all the synthesized Ru(ii) complexes.

Photovoltaic Properties and Long-Term Durability of Porphyrin-Sensitized Solar Cells with Silicon-Based Anchoring Groups

Anchoring groups for dye-sensitized solar cells (DSSCs) play a decisive role in high-power conversion efficiency (η) and long-term cell durability. To date, a carboxylic acid is the most widely used anchoring group for DSSCs. However, the carboxylic acid tends to dissociate from a TiO₂ surface during the cell operation as well as in the presence of water. Considering that the dye dissociation from TiO₂ leads to a decrease in the cell performance, stable anchoring groups are highly desirable to achieve long-term durability of DSSCs toward their practical application. In this study, we designed and synthesized a series of porphyrin dyes with the triethoxysilyl anchoring groups, ZnPSi1, ZnPSi2, and ZnPSi3, to evaluate the effects of the silicon-based anchoring group on cell durability and photovoltaic properties. The DSSCs based on ZnPSi1, ZnPSi2, and ZnPSi3 exhibited moderate η-values of 2.2, 4.7, and 2.3%, respectively. It is noteworthy that the η-value of the DSSC based on ZnPSi2 (4.7%) is the highest among DSSCs based on porphyrin dyes with silicon-based anchoring groups. The moderate η-values are mainly attributed to the low charge collection efficiency originating from the low surface coverage and plausible tilted geometry of the dyes on TiO₂. More importantly, we demonstrated that the DSSC based on ZnPSi2 revealed higher long-term cell durability under illumination than that based on reference porphyrin YD2 -o -C8 having a conventional carboxylic acid anchoring group.

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

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

Synthesis and Electrochemical and Photophysical Characterization of New 4,4'-π-Conjugated 2,2'-Bipyridines that are End-Capped with Cyanoacrylic Acid/Ester Groups

Two new functionalized 4,4'-disubstituted 2,2'-bipyridines that were end-capped with cyanoacrylic acid or cyanoacrylic acid ester anchoring groups, which might allow their efficient functionalization on TiO2 or other metal-oxide semiconductor surfaces, have been synthesized and characterized by electrochemical, photophysical, and spectroscopic measurements. The electrochemical and photophysical properties of these 4,4'-disubstituted 2,2'-bipyridines with extended π systems, in particular their LUMO energies, make them promising candidates to build up inorganic-organic hybrid photosensitizers for the sensitization of metal-oxide semiconductors (e.g., TiO2 nanoparticles and/or nanotubes).

Predicting Structures of Ru-Centered Dyes: A Computational Screening Tool

Dye-sensitized solar cells (DSCs) represent a means for harvesting solar energy to produce electrical power. Though a number of light harvesting dyes are in use, the search continues for more efficient and effective compounds to make commercially viable DSCs a reality. Computational methods have been increasingly applied to understand the dyes currently in use and to aid in the search for improved light harvesting compounds. Semiempirical quantum chemistry methods have a well-deserved reputation for giving good quality results in a very short amount of computer time. The most recent semiempirical models such as PM6 and PM7 are parametrized for a wide variety of molecule types, including organometallic complexes similar to DSC chromophores. In this article, the performance of PM6 is tested against a set of 20 molecules whose geometries were optimized using a density functional theory (DFT) method. It is found that PM6 gives geometries that are in good agreement with the optimized DFT structures. In order to reduce the differences between geometries optimized using PM6 and geometries optimized using DFT, the PM6 basis set parameters have been optimized for a subset of the molecules. It is found that it is sufficient to optimize the basis set for Ru alone to improve the agreement between the PM6 results and the DFT results. When this optimized Ru basis set is used, the mean unsigned error in Ru-ligand bond lengths is reduced from 0.043 to 0.017 Å in the set of 20 test molecules. Though the magnitude of these differences is small, the effect on the calculated UV/vis spectra is significant. These results clearly demonstrate the value of using PM6 to screen DSC chromophores as well as the value of optimizing PM6 basis set parameters for a specific set of molecules.

Positional isomerism makes a difference: phosphonic acid anchoring ligands with thienyl spacers in copper(i)-based dye-sensitized solar cells

With the aim of improving the photoconversion efficiencies of heteroleptic [Cu(Lanchor)(Lancillary)](+) dyes in n-type dye-sensitized solar cells (DSCs), the previously favoured anchor ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid) (1) has been replaced by analogues 2 and 3 containing 2-thienyl spacers between the 2,2'-bipyridine metal-binding domain and the phosphonic acid anchoring groups. The synthesis and characterization of 2 and 3 (2-thienyl spacer with phosphonic acid in the 5- and 4-positions, respectively) are reported. A stepwise, on-surface method was used to assemble [Cu(Lanchor)(Lancillary)](+) dyes onto FTO/TiO2 electrodes with Lanchor = 1, 2 or 3, and Lancillary = 6,6'-bis(trifluoromethyl)-2,2'-bipyridine (4), 6-trifluoromethyl-2,2'-bipyridine (5), 6,6'-dimethyl-2,2'-bipyridine (6), and 6-methyl-2,2'-bipyridine (7). Changing the solvent in the dye-bath from CH2Cl2 to acetone had only a small effect on the photoconversion efficiencies of [Cu(1)(4)](+), [Cu(1)(5)](+) and [Cu(1)(6)](+); the optimal dye in this series was [Cu(1)(5)](+). Comparable DSC performances were achieved by using either anchor 1 or 2, but there is improved electron injection if the phosphonic acid group is in the 4- rather than 5-position of the thienyl ring (i.e. anchor 3 is superior to 2). Similar open-circuit voltages (VOC) are achieved on going from 1 to 3 with a given Lancillary; although there is typically a gain in short-circuit current denisty (JSC) on going from 1 or 3 to 2, there is an ≈50-60 mV drop in VOC on introducing 2 as the anchor. The best photoconversion efficiencies are obtained for the dye [Cu(3)(5)](+) (η = 2.40% relative to an N719 reference of 5.76%). The conclusions reached from plots of current-density (J) against potential (V), and external quantum efficiency spectra are supported by electrochemical impedance spectroscopic measurements.

Ruthenium bistridentate complexes with non-symmetrical hexahydro-pyrimidopyrimidine ligands: a structural and theoretical investigation of their optical and electrochemical properties

The optical and electronic properties of six Ru complexes with non-symmetrical tridentate ligands have been investigated and, as corroborated by electrochemical data, the presence of the hpp ligand strongly affects the oxidation potential of the metal ion.

Tuning Thiophene-Based Phenothiazines for Stable Photocatalytic Hydrogen Production

Dibranched donor-(π-acceptor)2 dyes, where phenothiazine is the donor core, cyanoacrylic acid is the acceptor/anchoring group, and π is represented by mono- and poly-cyclic simple and fused thiophene derivatives, were tested as photosensitizers in the photocatalytic production of H2 , in combination with a Pt/TiO2 catalyst. The optical and electrochemical properties of the dyes were investigated, showing that careful design of the thiophene-based π spacer afforded enhanced optical properties. In the H2 production over 20 h, the new thiophene-based sensitizers revealed improved stability after longer irradiation times and enhanced performances, in terms of H2 production rates and light-to-fuel efficiencies, after an initial activation period, which were for the first time associated with enhanced stability under photocatalytic production of H2 and the absence of critical dye degradation.

Ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand for dye-sensitized solar cells: synthesis, photo- and electrochemical properties, and adsorption behavior to the TiO2 surface

Two novel ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand (TUS-35 and TUS-36) were synthesized to improve the molar absorptivity of the previously reported ruthenium sensitizer (TBA)[Ru{4'-(3,4-dicarboxyphenyl)-4,4″-dicarboxyterpyridine}(NCS)3], TBA = tetrabutylammonium (TUS-21). A relatively strong absorption appeared at ∼380 nm, and the molar absorption coefficient at the metal-to-ligand charge transfer (MLCT) band decreased in TUS-35 by introducing a 2-hexylthiophene unit to the 5-position of the terpyridine-derived ligand. For comparison, a relatively strong absorption was observed at ∼350 nm without decreasing the molar absorption coefficient at the MLCT band in TUS-36 by introducing a 2-hexylthiophene unit to the 4-position of the terpyridine-derived ligand. On the other hand, the energy levels of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals of these two sensitizers were found to be almost equal to those of TUS-21. The adsorption behavior of TUS-35 and TUS-36 was similar to that of (TBA)[Ru{4'-(3,4-dicarboxyphenyl)terpyridine}(NCS)3] (TUS-20), which binds to the TiO2 surface by using the 3,4-dicarboxyphenly unit, rather than that of TUS-21, which adsorbs to the TiO2 photoelectrode using one of the carboxyl groups at the terminal pyridines of the terpyridine-derived ligand. Therefore, TUS-35 and TUS-36 are considered to bind to the TiO2 surface by using the 3,4-dicarboxyphenly unit just like TUS-20. The dye-sensitized solar cells (DSCs) with TUS-35 and TUS-36 showed a relatively lower conversion efficiency (6.4% and 5.7%, respectively) compared to the DSC with TUS-21 (10.2%). Open-circuit photovoltage decay and electrochemical impedance spectroscopy measurements revealed that the promoted charge recombination and/or charge transfer of the injected electrons in the TiO2 photoelectrode is a main reason for the inferior performances of TUS-35 and TUS-36.

Novel heteroleptic Ru(ii) complexes: synthesis, characterization and application in dye-sensitized solar cells

Photovoltaic efficiencies of 6–8%, comparable with N719, were obtained with six novel Ru(ii) heteroleptic dyes.

Synthesis, photophysics and electrochemical properties of 1,1′-(2,2′-bithiophene-5,5′-diyl)bis(cycloalkeno[c]pyridine) as a result of the Diels–Alder reaction of 3-(2-thienyl)-1,2,4-triazine

Fused pyridine 2,2′-bithiophenes were prepared via [4+2] cycloaddition based on 3-(2-thienyl)-1,2,4-triazine, which was obtained by the Stille coupling reaction.

High extinction coefficient Ru-sensitizers that promote hole transfer on nanocrystalline TiO₂

Two series of Ru(II) polypyridyl compounds with formulas [(bpy)2RuL](PF6)2 and [(deeb)2RuL](PF6)2, where bpy is 2,2'-bipyridine, deeb is 4,4'-diethylester-2,2'-bpy, and L is one of several substituted 9'-(1,3-dithiole-2-ylidene)-4',5'-diazafluorene ligands, were studied as potential photosensitizers for TiO2. These compounds possess notably high extinction coefficients (≥40,000 M(-1) cm(-1) @470 nm) which are shown by time-dependent density functional theory (TD-DFT) calculations to result from overlapping metal-to-ligand charge transfer (MLCT) and ligand-localized transitions. Low-temperature absorption and photoluminescence measurements were suggestive of a short-lived MLCT excited state. When adsorbed onto TiO2 thin films, both the free ligands (L) and their corresponding [(deeb)2RuL](2+) complexes exhibited rapid excited-state electron injection into TiO2; in the case of the complexes, this was followed by rapid (k>10(8) s(-1)) hole transfer from Ru(III) to the 1,3-dithiole ring of the L ligand. Observation of diffusion-limited reductive quenching of the [Ru(bpz)3](2+)* (bpz is 2,2'-bipyrazine) excited state by the L ligands in solution supported the occurrence of intramolecular hole transfer following electron injection by the TiO2-anchored complexes.

Novel ruthenium sensitizers with a dianionic tridentate ligand for dye-sensitized solar cells: the relationship between the solar cell performances and the electron-withdrawing ability of substituents on the ligand

Five novel ruthenium sensitizers (TUS sensitizers) with a dianionic tridentate ligand (pyridine-2,6-dicarboxyamidato and its derivatives) have been synthesized for application to dye-sensitized solar cells (DSCs). These TUS sensitizers have much larger molar absorption coefficients in the wavelength range below 600 nm compared with those of Black dye which is a structural analog and a highly efficient ruthenium sensitizer. The energy levels of HOMOs and LUMOs of TUS sensitizers shifted to the positive direction with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The energy levels of HOMO and LUMO showed linear correlation with respect to the Hammett constant of the substituents. The DSCs with TUS sensitizers showed much lower performances than that of Black dye. Both inferior adsorptivity on the TiO2 surface and unfavorable energy levels of HOMOs and LUMOs for the effective electron transfer reactions in the DSCs are considered to be the main reasons for the much lower performances of TUS sensitizers. The conversion efficiency of the DSC with a TUS sensitizer increased with increasing the electron-withdrawing ability of the substituents on the dianionic tridentate ligand. The observed linear relationship between the conversion efficiency and the driving force of the reduction process of the oxidized form of dyes by I(-) suggests that the dye regeneration process is a rate-determining step in the DSCs with TUS sensitizers.

Ruthenium sensitizers having an ortho-dicarboxyl group as an anchoring unit for dye-sensitized solar cells: synthesis, photo- and electrochemical properties, and adsorption behavior to the TiO2 surface

A novel ruthenium sensitizer with a 3′,4′-dicarboxyterpyridine (TUS-28) has been synthesized as an improved model sensitizer of the dye-sensitized solar cells.

New ruthenium sensitizers featuring bulky ancillary ligands combined with a dual functioned coadsorbent for high efficiency dye-sensitized solar cells

Two ruthenium complexes featuring bulky ancillary ligands, XS48 and XS49, were synthesized and studied as dyes in dye-sensitized solar cells (DSCs). Both dyes exhibit higher solar-to-electrical energy conversion efficiency when compared to a commonly used N3 sensitizer under the same conditions. To examine the influence of the bulky ancillary ligands and alleviate the electron recombination in cells, we have developed a dual functioned truxene-based coadsorbent (MXD1) as an alternative candidate to chenodeoxycholic acid (CDCA). This coadsorbent not only effectively shields the back electron transfer from the TiO(2) to I(3)(-) ions but also enhances the light harvesting ability in the short wavelength regions. The photovoltaic performance of XS48-sensitized DSC was independent of the coadsorbents, while XS49 with large bulky ancillary ligand presented better performance when coadsorbent was employed. Interestingly, the simultaneous adsorption-to-sequential adsorption of XS48/49 and MXD1 has caused a notably improved photovoltage, which can be primarily ascribed to the enhanced dye adsorption and retardation of charge recombination. These results not only provide a new vision on how ancillary ligands affect the performance of ruthenium complexes but also open up a new way to achieve further efficiency enhancement of ruthenium complexes.

A bis(terpyridine)ruthenium complex with three redox-active amine sites: electrochemical, optical, and computational studies

Two ruthenium complexes, [Ru(NN)(ttpy)](2+) and [Ru(NN)(daatpy)](2+), have been designed and prepared, where NN is bis(amine) ligand 4'-tolyl-5,5"-bis(di-p-anisylamino)-2,2':6',2"-terpyridine, ttpy is 4'-tolyl-2,2':6',2"-terpyridine, and daatpy is 4'-di-p-anisylamino-2,2':6',2"-terpyridine. Complex [Ru(NN)(daatpy)](2+) contains three redox-active amine groups and has been characterized by single-crystal X-ray analysis. These two complexes display much-enhanced light absorption capabilities with respect to the prototype compound [Ru(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine), which has been rationalized on the basis of time-dependent density functional theory calculations. Electrochemical and optical studies showed that there was little electronic coupling between two amine sites in complex [Ru(NN)(ttpy)](2+). On the other hand, a ligand-to-ligand (N → N'(•+)) charge-transfer band has been observed at 1430 nm for singly and doubly oxidized forms of [Ru(NN)(daatpy)](2+), and an electronic coupling parameter of 1000 cm(-1) was derived using the Hush formula. This band is interpreted as a charge transfer from the neutral amine of the daatpy ligand to oxidized aminium units in the NN ligand.

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Molecular engineering of sensitizers for dye-sensitized solar cell applications

Dye-sensitized solar cells (DSSCs) have attracted considerable attention in recent years as they offer the possibility of low-cost conversion of photovoltaic energy. This account focuses on recent advances in molecular design and technological aspects of sensitizers based on metal complexes, metal-free organics and tetrapyrrolic compounds which include porphyrins, phthalocyanines as well as corroles. Special attention has been paid to the design principles of these dyes, and co-sensitization, an emerging technique to extend the absorption range, is also discussed as a way to improve the performance of the device. This account also focuses on recent advances of efficient ruthenium sensitizers as well as other metal complexes and their applications in DSSCs. Recent developments in the area of metal-free organic and tetrapyrrolic sensitizers are also discussed.