Panchromatic Absorption Research Articles

The mercurial rise in research of halide perovskites: what´s next

AbstractPerovskites are of high potential in the ongoing academic research, due to their distinctive electrical properties and crystalline structures. Halide perovskites show high light emissive properties and panchromatic light absorption across the visible spectrum. The exceptional electrical characteristics, such as their long carrier lifespan, high diffusion length, and charge carrier mobility, allow the electric charges to be transported and collected effectively. Furthermore, by tuning the cations and anions composition, perovskite’s opto-electrical properties can be altered. Moreover, dimension reduction affects their band gap and intrinsic features to induce higher structural stability but at the cost of the quantum confinement effect. Owing to their exceptional properties, halide perovskites are being researched in energy-related and semiconducting applications, hold high promise and the future looks bright. But challenges remain, and the larger question is what needs to be done to make them more stable.

Enhanced performance of dye-sensitized solar cells via anthocyanin, chlorophyll, benzothiadiazole and diphenylacridine co-sensitizers and amine-based co-adsorbents

Anthocyanin (ANT) and chlorophyll (CHL) natural dyes extracted from blue butterfly pea flowers and spinach leaves and two synthetic metal-free dyes (BIM33 and C1) were evaluated as sensitizers/co-sensitizers in dye-sensitized solar cells (DSSCs). To suppress the possible dye aggregation, triethylamine (TEA) and diethylenetriamine (DETA) were utilized as alternative co-adsorbents to the commonly used chenodeoxycholic acid (CDCA). Furthermore, CHL, BIM33, and C1 were co-sensitized with ANT to achieve panchromatic light absorption and, hence, enhance the photovoltaic performance. Therefore, the power conversion efficiencies (PCEs) of DSSCs based on the dyes were significantly improved from 1.19–5.01 % to 2.39–6.31 % by the co-sensitization and utilization of co-adsorbents. Meanwhile, the efficiencies of DSSCs based on TEA or DETA were superior to those based on CDCA under the same conditions. This study provides effective strategies for improving the performance of DSSCs based on environment-friendly dyes.

Platinum-Centered Oligoynes Capped by Boron Difluoride Formazanate Dyes and Their Thin-Film Properties.

Since the Nobel prize winning discovery that polyacetylene could act as a semiconductor, there has been tremendous efforts dedicated to understanding and harnessing the unusual properties of 𝜋-conjugated polymers. Much of this research has focused on the preparation of oligoynes and polyynes with well-defined numbers of repeating alkyne units as models for carbyne. These studies are usually hampered by a structure-property relationship where the stability of the resulting materials decrease with the incorporation of additional alkyne units. Here, we describe a series of oligoynes, with up to 12 alkyne units, where electron-rich [Pt(PBu3)2]2+ units are incorporated into the center of oligoyne backbones which are capped by electron-poor BF2 formazanate dyes. These compounds exhibit excellent stability and solubility, panchromatic absorption, and redox activity characteristic of their structural components. These traits facilitated thin-film studies of extended oligoyne materials, where it is shown that incorporating [Pt(PBu3)2]2+ units leads to smoother films, decreased conductivity on the microscale, and increased conductivity on the nanoscale when compared to metal-free analogs. Remarkably, our oligoynes have superior conductivity compared to the ubiquitous poly(3-hexylthiophene) semiconductor.

Synthesis, Structural, Electrochemical, and DFT Studies of Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent Third-Order Nonlinear Optical Properties.

We designed and successfully synthesized highly substituted electron-deficient nonplanar Ni(II) porphyrins and their derivatives (1-7) in moderate to good yields. These derivatives were comprehensively characterized by various spectroscopic techniques and single-crystal X-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures of compounds 2, 4, and 7, adopting saddle-shape geometry. These nonplanar porphyrins demonstrated significant bathochromic shifts in their absorption spectra compared to parent NiTPP, attributed to the influence of bulky β-substituents and/or peripheral fusion. π-Extended porphyrins 6 and 7 displayed panchromatic absorption spectra extending into the NIR region. Porphyrins 6 and 7 demonstrated a profound anodic shift (∼400 mV) in their first reduction peak potentials compared to precursor NiTPP(NO2)Br6. The experimental absorption spectral pattern matches the simulated absorption spectra obtained from TD-DFT studies. The femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that NiDFP(VCN)2Br6 (6) and NiDFP(VCN)2(PE)6 (7) displayed giant optical nonlinearities compared to the other porphyrins. Among all, NiDFP(VCN)2Br6 (6) possessed the highest two-photon absorption coefficient (β) and cross-section (σTPA) values in the range of 22-33 × 10-10 m/W and 3.77-6.95 × 106 GM, respectively. These findings suggest that the investigated nonplanar π-extended porphyrins are promising candidates for future optoelectronic applications.

Ultrafast Near‐Infrared Luminescence from Cyclometalated Iridium(III) Complexes with Indirubin as Ancillary Ligand

AbstractBeing a constitutional isomer of the indigo dye, indirubin has been known as a purple colourant for a long time. On the other hand, its structural and photophysical properties as ligand in metal complexes are virtually unexplored. Herein, for the first time, we utilized indirubin as ancillary chelator to develop two new heteroleptic iridium(III) complexes equipped with two 2‐phenylpyridine units as archetypical cyclometalating ligands. These new complexes display fully reversible oxidation and reduction processes, and show a panchromatic absorption extending up to 900 nm in acetonitrile solution at 298 K. Moreover, an unexpected broad and unstructured emission band is detected for both complexes in the near‐infrared region, peaking at approx. 1100 nm and having a lifetime of approx. 60 ps; such an emission is attributed to a ligand‐centred triplet excited state (3LC) located on the indirubin ligand itself, as proved by DFT calculations. These findings may pave the way for further exploration of the indirubin dye as a ligand for different types of metal centres to create efficient near‐infrared triplet emitters without the need for difficult synthetic procedures.

Rational Design and Engineering of Terminal Functional Groups in Dibenzothiophene‐Diphenylamine Small Molecular Electron Donors for Enhanced Photovoltaic Efficiency in All‐Small‐Molecule Organic Solar Cells

AbstractAll‐small‐molecule organic solar cells (ASM‐OSCs) offer advantages like well‐defined molecular structures and excellent reproducibility. However, lower photovoltaic efficiencies hinder their adoption due to limitations in designing small molecular electron donors (SMEDs) with optimal energy levels, light absorption, and optoelectronic properties. The present study addresses this gap by rationally designing a series of SMEDs (DBT‐2FA1 to DBT‐2FA6) through terminal acceptors engineering into dibenzothiophene core with diphenylamine side donors for potential applications in ASM‐OSCs. Density functional theory simulations are carried‐out to establish structure‐property relationships based on structural, electrochemical, photophysical, and charge transfer (CT) properties. Results show that the SMEDs exhibit low‐lying HOMOs for suitable energy level alignment with benchmark Y6 acceptor, promoting open‐circuit voltage and charge separation. The panchromatic absorption spectra covering Vis‐NIR region and maximum light harvesting efficiency are beneficial for high current‐density in ASM‐OSCs. Notably, the push‐pull mechanism within SMEDs results in dominant intramolecular CT with above 70% CT excitations. Whereas, a moderate variation in dipole moments and electrostatic potential differences with acceptor material led to 99.9% intermolecular CT, thus ensuring robust exciton dissociation and efficient photocurrent generation. Overall, this work provides a molecular‐level understanding of designing novel SMEDs and their compatibility with acceptor materials for developing future high‐performance ASM‐OSCs.

Ultrafast and Quantitative FRET Sensitization of Singlet Fission in Solution‐Processable Para‐Azaquinodimethane Films

AbstractIn this work, a green protocol for the synthesis of new para‐Azaquinodimethane (pAQM) small molecules, functionalized with anisole (An) or bithiophene (TT) moieties on the central unit and with different alkoxy groups as lateral substituents is developed and reported. The alkoxy lateral substituents are found to strongly impact the solubility and processability of the chromophores. On the other hand, the steady–state and time‐resolved spectroscopic results show completely different spectral and photophysical features for the An‐ and TT‐ derivatives. Only for the TT‐compounds, the nanosecond and femtosecond transient absorption experiments reveal low efficiency of triplet production in solution as well as ultrafast (≈1 ps) and efficient (≈200%) singlet fission (SF) in thin film. The yellow An‐containing molecules are instead used to sensitize the purple SF‐active TT‐compounds via quantitative FRET in mixed thin films, which interestingly exhibit panchromatic absorption extending in the entire visible spectral range. With this study, the synergy between FRET and SF is exploited at the intermolecular level in the solid‐state for the first time by considering unconventional and stable SF chromophores, opening intriguing new possibilities for solar energy harvesting.

Photothermal Conversion Perylene-Based Metal-Organic Framework with Panchromatic Absorption Bandwidth across the Visible to Near-Infrared.

Recently, facilely designable metal-organic frameworks have gained attention in the construction of photothermal conversion materials. Nonetheless, most of the previously reported photothermal conversion metal-organic frameworks exhibit limited light absorption capabilities. In this work, a distinctive metal-organic framework with heterogeneous periodic alternate spatial arrangements of metal-oxygen clusters and perylene-based derivative molecules was prepared by in situ synthesis. The building blocks in this inimitable structure behave as both electron donors and electron acceptors, giving rise to the significant inherent charge transfer in this crystalline material, resulting in a narrow band gap with excellent panchromatic absorption, with the ground state being the charge transfer state. Moreover, it can retain excellent air-, photo-, and water-stability in the solid state. The excellent stability and broad light absorption characteristics enable the effective realization of near-infrared (NIR) photothermal conversion, including infrequent NIR-II photothermal conversion, in this perylene-based metal-organic framework.

Mixed‐Tetravalent Cs2RumPt1−mX6 (X = Cl−, Br−)‐Based Vacancy‐Ordered Halide Double Perovskites for Enhanced Solar Water Oxidation

Vacancy‐ordered halide double perovskites (VOPs) are reported to be suitable for photoelectrochemical (PEC) water splitting, due to their panchromatic visible absorption and stability in electrolyte. In this work, ruthenium‐based VOP, Cs2RuX6 (X = Cl−, Br−), is reported for PEC water splitting, and the material is found to be extremely stable in harsh pH media, between pH1 and pH11. The PEC devices made with these materials show good photogenerated hole transport to electrolyte; however, the photovoltage remains low due to high recombination. To enhance the performance, Ru4+ is partially substituted with Pt4+ tetravalent cation, where the latter is shown to possess better photovoltage. The mixed‐tetravalent compound, Cs2RumPt1−mX6, leads to high PEC water oxidation current at m = 0.5, compared to their end members. The mixed‐tetravalent compounds show a synergic effect of reduced charge‐transfer resistance from the material to the electrolyte and increased photovoltage leading to increased PEC performance.

The effects of alkyl substitution on the aggregation of π-conjugated dyes: spectroscopic study and modelling.

A family of dithienosilole-based dyes with alternating donor and acceptor conjugated groups, decorated with linear or branched alkyl chains at different positions on the backbone, have been obtained and investigated in different aggregation states. These dyes are characterized by almost panchromatic absorption and by near-IR emission, with good quantum yields in a variety of solvents with different polarity. We demonstrate that the nature and position of the alkyl substituents strongly govern the self-assembly of the dyes, whose packing is also sensitive to external stimuli, such as grinding and water addition. Thanks to computational results and theoretical modelling, we are able to interpret the results based on two possible preferential packings, characterized by distinct spectroscopic behaviour, whose abundance can be tuned according to the nature and position of the alkyl chains, as well as via external stimuli.

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.

β-meso-Fused pyrene-porphyrin scaffolds with panchromatic absorption features.

The π-extension of porphyrins with pyrenes through the β-meso-fusion of five-membered rings is demonstrated. Three architectures resulting from combining up to two porphyrins and pyrenes were obtained straightforwardly in good overall yields. Although significantly planarized, the molecules retain excellent solubility and processability. Spectroscopic characterization and density-functional theory calculations reveal intriguing absorption features.

Side‐Chain Engineering of Y‐Series Acceptors with Halogenated End‐Group for Efficient Indoor Organic Photovoltaics

AbstractDiverse design strategies for nonfullerene acceptors (NFAs) have aided the development of efficient indoor organic photovoltaics (OPVs) for Internet‐of‐things‐enabled gadgets. However, the side‐chain approach to Y‐series NFAs for fabricating indoor OPVs remains largely unexplored. In this study, the synthesis and photovoltaic characteristics of two side‐chain engineered NFAs with halogenated end‐groups (BTP‐PO‐4F and BTP‐PO‐4Cl) are investigated. NFAs with a Y6 core unit are modified with butyloctyl inner side chains and ethylhexyloxynaphthyl outer side chains. The extended conjugation moiety contributed to red‐shifted absorption, with the chlorination effect presenting a more pronounced influence than fluorination. Further, the outer moiety introduced a slight electron‐withdrawing effect on the Y6 core unit, resulting in energy‐level downshifts. An excellent power conversion efficiency (PCE) of 23.2% is achieved in fluorinated OPVs under a light‐emitting diode lamp (1000 lux). Moreover, integrating the Y6 NFA into the binary blend further enhanced the PCE, reaching 28.3% in PM6:Y6:halogenated NFA ternary OPVs. The panchromatic absorption, high crystallinity, and cascaded energy levels of the ternary blends contribute to achieving a sufficient spectral match and suppress trap‐assisted recombination, ultimately fostering a substantially enhanced fill factor and PCEs under indoor lighting.

Panchromatic and Perturbed Absorption Spectral Features and Multiredox Properties of Dicyanovinyl- and Dicyanobutadienyl-Appended Cobalt Corroles.

Four new β-functionalized π-extended cobalt corroles with one and two dicyanovinyl (DCV) or dicyanobutadienyl (DCBD) moieties at the 3- and 3,17-positions have been synthesized and characterized by various spectroscopic techniques. Interestingly, the synthesized DCV- and DCBD-appended cobalt corroles displayed panchromatic and near-infrared absorption in the range 300-1100 nm in CH2Cl2 and pyridine solvents. (MN)2-(Cor)Co and A2MN2-(Cor)Co exhibited 8-9 times enhancement in the molar absorptivity of the Q band compared to the parent corrole ((Cor)Co). The unique absorption spectral features of these β-functionalized cobalt corroles are splitting, broadening, and red-shifting in the Soret and Q bands. One DCV unit brings a 30-46 nm red shift, whereas one DCBD unit brings a 40-75 nm red shift in the Q band compared to the corresponding precursors. This is rare that the intensity of the longest Q band is greater than or equal to the Soret-like bands. These corrole derivatives exhibit UV-vis spectral features similar to those of chlorophyll a. A 220 mV positive shift per DCV group and 160 mV positive shift per DCBD group were observed in the first oxidation potentials compared to (Cor)Co in the desired direction for the utility of these cobalt complexes in electrocatalysis. DFT studies revealed that HOMO and LUMO were stabilized after appending DCV and DCBD groups on the corrole macrocycle and exhibited a "push-pull" behavior leading to promising material applications in nonlinear optics (NLO) and catalysis.

Synthesis and Characterization of Quinone Compounds Derived from Doubly and Triply Linked Diporphyrins and Tuning of Their Absorption Properties.

Porphyrins are attracting increasing attention in materials science and photochemistry owing to their unique properties and diverse applications. This study focuses on modifying and tuning the absorption properties of porphyrins, specifically those of quinoidal porphyrins, to extend their spectral range into the near-infrared (NIR) region. We report the synthesis and structural and physical properties of quinone compounds derived from doubly and triply linked diporphyrins and their metal complexes. Doubly linked diporphyrinquinone exhibits broad panchromatic absorption properties in solution owing to its low symmetry. Metal complexation markedly extends its absorption range into the near-infrared region. In contrast, the metal complexes of the triply linked diporphyrinquinones exhibit sharp and strong absorption bands in the visible to near-infrared region owing to their higher symmetry. The longest absorption wavelength of the triply linked diporphyrinquinones was approximately 1500 nm, which was significantly more red-shifted than that of the doubly linked ones.

Solar cells based on doubly concerted companion dyes with the efficiencies modulated by inserting an ethynyl group at different positions

To develop efficient sensitizers for dye-sensitized solar cells (DSSCs), we recently reported doubly concerted companion (DCC) dye XW83 with a wrapped porphyrin sub-dye unit linked to an organic sub-dye unit through a flexible chain, which exhibits panchromatic absorption and excellent anti-aggregation ability. To further improve the absorption, we herein report XW87 and XW88 by inserting an ethynyl group into the organic sub-dye unit of XW83 near the donor and acceptor, respectively. For the corresponding organic dyes Z3 and Z4, the introduced ethynyl group improves their absorption, but induces aggravated charge recombination, leading to lowered power conversion efficiencies (PCEs). Similar to the organic dyes, the introduced ethynyl group improves the absorption of DCC dyes XW87 and XW88 as well. In addition, the ethynyl group near the acceptor of the organic sub-dye unit can be well protected by the long wrapping chains from the porphyrin unit. As a result, XW88 affords the highest JSC (21.84 mA/cm2), VOC (782 mV) and PCE (12.2%) among the DCC dyes. These results provide an effective method for developing efficient DSSC dyes by inserting an ethynyl group at a suitable position of a DCC dye.

Controlling the TiO2–Dye Nanomolecular Interactions for Improving the Photoconversion in Transparent Dye‐Sensitized Solar Cells

Herein, transparent dye‐sensitized solar cells (DSSCs) are fabricated using two sensitizing dyes aiming toward panchromatic photon harvesting following two different approaches of dye adsorption such as using dye cocktail and sequential dye adsorption. A combination of complementary yellow‐colored dye (D‐131) and green‐colored far‐red‐sensitive squaraine dye (SQ‐140) is judiciously selected not only for panchromatic light absorption but also for bypassing the absorption in the high eye‐sensitivity wavelength region (500–600 nm) region to improve the transparency. The DSSC fabricated using a dye cocktail of D‐131 and SQ‐140 in a 9:1 molar ratio exhibits a photoconversion efficiency (PCE) and average visible transparency (AVT) of 3.89% and 36.9%, respectively. In contrast, stepwise and controlled dye adsorption of SQ‐140 followed by D‐131 on mesoporous TiO2 leads to further improvement in the PCE from 3.89% to 4.50%, while AVT is reduced from 36.9% to 15.6%. This marked improvement in the PCE for the stepwise co‐sensitized transparent DSSCs is attributed to the suppression of unfavorable inter‐dye interaction leading to synergistic photon harvesting by both of the constituent sensitizing dyes.

Tetracyanobuta-1,3-diene (TCBD)-appended pyrrolopyrrole aza-BODIPYs as a panchromatic chromophore based on the push-pull strategy

Pyrrolopyrrole aza-BODIPY (PPAB), a dimeric BODIPY analogue containing a pyrrolopyrrole structure at the center, exhibits intense far-red and near-infrared (NIR) absorption and emission. Herein, tetracyanobuta-1,3-diene-appended PPABs (TCBD-PPABs) were synthesized by post-modification based on a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethylene. Owing to the redshift of the PPAB absorption in the NIR region and the emergence of the intramolecular charge-transfer band in the visible region, TCBD-PPABs exhibit panchromatic absorption in the visible/NIR regions.

Stable Spiro-Fused Diarylaminyl Radicals: A New Type of a Neutral Mixed-Valence System.

A new type of neutral mixed-valence system was synthesized using a facile one-pot procedure. The spiro-conjugated framework is additionally "fastened" with a biphenyl bridge, which does not directly participate in spin delocalization but makes the molecule stable and influences the reorganization energy and the energy barrier of the intramolecular electron transfer. The in-depth experimental and quantum-chemical study allowed determining the radicals as the Class II Robin-Day-mixed-valence systems. The structure of the radicals was confirmed by the X-ray data, which are relatively rare for Class II MV molecules. Advanced properties of the radicals, such as an ambipolar redox behavior and panchromatic absorption in the visible and NIR regions, along with their stability, make them of interest for materials science. All radicals demonstrate the SOMO-HOMO inversion phenomenon, which was supported by the DFT and the experimental study.

Panchromatic NIR-Absorbing Sensitizers with a Thienopyrazine Auxiliary Acceptor for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) are a cost-effective and highly tunable technology for harvesting solar energy. Current research is focused on the design of near-infrared (NIR, >700 nm) absorbing organic sensitizers to efficiently harvest low-energy photons to increase the efficiency of DSCs. Herein, two NIR sensitizers containing a proaromatic thienopyrazine (TPZ) auxiliary acceptor are synthesized. The optical, electrochemical, and device properties of the sensitizers were studied. The two dyes probe the placement of the TPZ auxiliary acceptor (A′) either between the π-bridge and the acceptor (WM1, D−π–A′−A) or between the donor and the π-bridge (WM2, D–A′−π–A). WM1 and WM2 exhibit absorption maxima at 631 and 604 nm in dichloromethane (DCM), respectively. Both dyes also have higher energy absorption features, which contributes to panchromatic absorption into the NIR region. Optimized devices were sequentially sensitized with Y123 to control the surface conformation of the TPZ dyes, yielding high photocurrent values of 20.3 and 14.4 mA/cm2 for WM1 and WM2, respectively. WM1 exhibits a low-energy NIR incident photon-to-current efficiency (IPCE) onset at ∼900 nm.