Combined Experimental and DFT-TDDFT Computational Study of Photoelectrochemical Cell Ruthenium Sensitizers

International conference on "Photosynthesis and Hydrogen Energy Research for Sustainability-2023": in honor of Robert Blankenship, Győző Garab, Michael Grätzel, Norman Hüner and Gunnar Öquist

The 11th International Photosynthesis Conference on Hydrogen Energy Research and Sustainability 2023 was organized in honor of Robert Blankenship, Győző Garab, Michael Grätzel, Norman Hüner, and Gunnar Öquist, in Istanbul, Türkiye at Bahçeşehir University Future Campus from 03 to 09 July 2023. It was jointly supported by the International Society of Photosynthesis Research (ISPR) and the International Association for Hydrogen Energy (IAHE). In this article we provide brief details of the conference, its events, keynote speakers, and the scientific contribution of scientists honored at this conference. Further, we also describe the participation of young researchers, their talks, and their awards.

Exploring the synergy between copper electrolytes and molecularly engineered thiocyanate-free cyclometalated ruthenium sensitizers for dye-sensitized solar cells

Two novel cyclometalated ruthenium complexes, RC-4 and RC-5, featuring 1-phenylisoquinoline and phenyl quinazoline as ancillary ligands, respectively, were synthesized to investigate their viability with the environmentally friendly copper (Cu) redox mediator, [Cu(bpye)2]2+/+. The modification of the ligand environment resulted in variations in the energetics, photophysical properties, and photovoltaic performance of RC-4 and RC-5 sensitizers. Despite RC-5 sensitizer possessing a more positive ground state potential of 1.19 V versus the NHE, the RC-4 sensitizer, with a lower HOMO level of 0.72 V versus NHE, exhibited superior photovoltaic performance along with the Cu electrolyte, attributed to its enhanced light harvesting ability, improved lifetime and reduced back electron transfer, contributing to higher Jsc, Voc, and PCE.

4-Carboxyphenyl as efficient donor group in nano Zn-Porphyrin for dye sensitized solar cells

Dye-sensitized solar cells, represent the alternate technology in solar research due to their cost effective, easy fabrication processes, higher efficiencies, and design flexibility. In this research, dual donor group modified zinc porphyrin dyes, have been synthesized for DSSCs. The complexes of zinc porphyrin functioned as acceptor or attaching groups within each mesophenyl ring and carboxylic acid. These complexes exhibited diverse alkyl substituents and sizable electron-donating substituents, contributing to their varied chemical structures and potential applications. The dual Donor-π bridge -Acceptor group sensitizers, Zn[5,15-diphenylcarbazole-10,20-(4-carboxyphenyl) Porphyrin] (KSR-1) and Zn [5,15-thiadiazole-10,20-(4-carboxyphenyl) Porphyrin] (KSR-2) have been synthesized and adopted for DSSCs implementation. The molar absorption coefficients (ε) of KSR-2 and KSR-1 Soret bands were 0.56 x 105 mol/L/cm and 0.47 x 105 mol/L/cm, respectively. The Q bands of the KSR-1 and KSR-2 dyes were 1.10 x 105 mol/L/cm and 1.0 x 105 mol/L/cm, respectively and the molar absorption coefficient of the KSR-1 dye was greater when compared to the KSR-2 dye. The molar absorption coefficient of 0.71 x 105 mol/L/cm was visible in the KSR -1 Q-band. DFT calculations and the electrochemical characteristics of the KSR-1 and KSR-2 dyes have been studied and discussed. The exploration involved in investigating the photophysical properties and photovoltaic performance which were affected by varying the length and number of the donor entities. The wall-plug efficiency of the KSR-1 based solar panel was Voc = 0.68 V, Jsc = 8.94 mA/m2, FF = 56 and Efficiency (μ) = 3.44%. The wall-plug efficiency of the KSR-2 based solar panel was Voc = 0.63 V, Jsc = 5.42 mA/m2, FF = 53 and Efficiency (μ) = 1.83%.

Design a New D-π-A Formation Dyes as Dye-sensitized Solar Cells Applications/ a DFT and TD-DFT Study

Dye-sensitized solar cells (DSSCs) have garnered significant interest among researchers in the field of photovoltaics due to their promising performance, low cost and easy process of fabrication. In this study, we have designed new D-π-A systems as derivatives of the reference (Ref. A) D-A-D scaffold, incorporating different π-bridges to enhance and optimize their efficiency as sensitizing dyes for DSSCs applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were employed to investigate the geometrical and electronic structures, chemical reactivity indices, optical properties, exciton binding energy, and electrochemical properties of these dyes. We also examined the preferred adsorption process of the two selected dyes on a (TiO2)15 cluster model. The results demonstrate that all the dyes exhibit improved open-circuit photovoltage, enhanced light-harvesting efficiencies, higher electron injection efficiency, and excellent photovoltaic efficiency. Moreover, there is evidence of electron injection occurring from each studied dye to the conduction band of TiO2, followed by efficient regeneration. The introduced bridges in the molecular systems play a crucial role in facilitating electron transfer from the donor to the acceptor region. Comparatively, the D-π-D systems exhibit superior performance in DSSCs compared to Ref. A, which can be attributed to their higher energy levels of the lowest unoccupied molecular orbital and larger oscillator strengths for the most excited states involving intramolecular electron transfer and the electron injection process occurring from each examined molecule to the conduction band of TiO2, followed by subsequent regeneration. Overall, the results of our study highlight the potential of all the D-π-A systems as promising sensitizers for DSSCs applications, owing to their favorable optical and electronic properties and impressive photovoltaic parameters.

Recent developments, advances and strategies in heterogeneous photocatalysts for water splitting

Photocatalytic water splitting (PWS) is an up-and-coming technology for generating sustainable fuel using light energy. Significant progress has been made in the developing of PWS innovations over recent years. In addition to various water-splitting (WS) systems, the focus has primarily been on one- and two-steps-excitation WS systems. These systems utilize singular or composite photocatalysts for WS, which is a simple, feasible, and cost-effective method for efficiently converting prevalent green energy into sustainable H2 energy on a large commercial scale. The proposed principle of charge confinement and transformation should be implemented dynamically by conjugating and stimulating the photocatalytic process while ensuring no unintentional connection at the interface. This study focuses on overall water splitting (OWS) using one/two-steps excitation and various techniques. It also discusses the current advancements in the development of new light-absorbing materials and provides perspectives and approaches for isolating photoinduced charges. This article explores multiple aspects of advancement, encompassing both chemical and physical changes, environmental factors, different photocatalyst types, and distinct parameters affecting PWS. Significant factors for achieving an efficient photocatalytic process under detrimental conditions, (e.g., strong light absorption, and synthesis of structures with a nanometer scale. Future research will focus on developing novel materials, investigating potential synthesis techniques, and improving existing high-energy raw materials. The endeavors aim is to enhance the efficiency of energy conversion, the absorption of radiation, and the coherence of physiochemical processes.

Enhancing Near-Infrared Absorption in Terpyridyl Ru/Os Complexes with Ancillary Ligands to Activate Spin-Forbidden Transitions in Dye-Sensitized Solar Cells: A TDDFT Investigation

Dye sensitizers with wideband absorption covering the near-IR region have long been of interest because they potentially harvest a wide range of solar energies essential to promote photocurrent power conversion efficiencies. In this study, we used time-dependent density functional theory with spin-orbit (SO) interactions to theoretically explore the long-wavelength absorptions and spin-forbidden triplet transitions activated by SO interactions for terpyridyl ruthenium/osmium complex dyes. These dyes feature a Ru(II) sensitizer coordinated with a phosphine ligand and are exemplified by DX1, denoted as [trans-dichloro-(phenyldimethoxyphosphine)(2,2';6',2″-terpyridyl-4,4',4″-tricarboxylic)Ru]. We found that ancillary ligands significantly affected the longest wavelength spin-allowed absorption, with NCS- ligands yielding longer wavelength S1 transitions than halides. High atomic number halide ligands caused blue shifts in the S1 transition. Os complexes consistently exhibited longer wavelength S1 transitions than Ru complexes with identical ligands. In Ru/Os complexes, ancillary ligands with higher atomic numbers have a more pronounced effect in activating spin-forbidden triplet transitions through spin-orbit coupling (SOC) than those with lower atomic numbers. The absorption wavelength of the SOC-activated transition primarily depended on the energy of lower lying triplet states. Some complexes exhibited T1 states activated by SOC, leading to longer wavelength absorption than that of SOC-activated T2 states. Our study revealed the significance of ancillary ligands and SOC interactions in Ru/Os complexes, offering insights for optimizing materials with enhanced long-wavelength absorption properties, particularly in the near-IR range, for photovoltaic and optoelectronic applications.

A theoretical study on the role of the π-spacer in the thoughtful design of good light-absorbing dyes with phenothiazine for efficient dye-sensitized solar cells (DSSCs)

CONTEXT

In this work, we designed ten new organic phenothiazine dyes bridged by different πi-spacers (PTZ1-PTZ10) of D-π-A type based on the synthesized dye CC202-III for their efficacy in dye-sensitized solar cells (DSSC) applications. To learn how various π-spacers affect their performance in DSSCs, these isolated dyes and dye-cluster systems have had their geometries, electronic structures, absorption spectra, dipole moments, and molecular electrostatic potential examined and talked about. Additionally, a number of quantization parameters that affect power conversion efficiency (PCE), including light collection efficiency (LHE), reorganization energy (λtotal), vertical dipole moment (μnormal), strength electron injection driving force (ΔGinject), regeneration driving force (ΔGreg), excited state lifetime (τ), and open circuit voltage (VOC), were calculated in order to identify the organic dyes that would be best suited for DSSC applications. Calculated results revealed that the designed dyes PTZ3, PTZ4, PTZ5, and PTZ10 exhibit a lower energy gap among all dyes compared to the corresponding CC202-III. Additionally, PTZ3, PTZ4, PTZ5, PTZ7, PTZ8, PTZ9, and PTZ10 exhibit significant red-shifted absorption spectra compared to the other dyes with a larger oscillator strength, which improves the photocurrent density of the devices. The findings thus imply that bridge modification is a workable tactic to raise DSSC effectiveness.

METHOD

We used density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to study the electronic and photovoltaic properties of the dyes designed (PTZ1-PTZ10) to assess their effectiveness in DSSCs. DFT and TD-DFT simulations are theoretically used to deeply analyze key characteristics of all organic dyes that affect open-circuit voltage (VOC) and short-circuit current (JSC) to identify structure-property relationships.

Bifunctionality of dirhodium tetracarboxylates in metallaphotocatalysis

Metallaphotocatalysis has been recognized as a pivotal catalysis enabling new reactivities. Traditional metallaphotocatalysis often requires two or more separate catalysts and exhibits flaw in cost and substrate-tolerance, thus representing an await-to-solve issue in catalysis. We herein realize metallaphotocatalysis with a bifunctional dirhodium tetracarboxylate ([Rh2]) alone. The [Rh2] shows an photocatalytic activity of promoting singlet oxygen (1O2) oxidation. By harnessing its photocatalytic activity, the [Rh2] catalyzes a photochemical cascade reaction (PCR) via combination of carbenoid chemistry and 1O2 chemistry. The PCR is characterized by high atom-efficiency, excellent stereoselectivities, mild conditions, scalable synthesis, and pharmaceutically interesting products. DFT calculations-aided mechanistic study rationalizes the reaction pathway and interprets the origin of stereoselectivities of the PCR. The products show inhibitory activity against PTP1B, being promising in the treatment of type II diabetes and cancers. Overall, here we show the bifunctional [Rh2] merges Rh-carbenoid chemistry and 1O2 chemistry.

Isocyanides as Catalytic Electron Acceptors in the Visible Light Promoted Oxidative Formation of Benzyl and Acyl Radicals

The recent disclosure of the ability of aromatic isocyanides to harvest visible light and act as single electron acceptors when reacting with tertiary aromatic amines has triggered a renewed interest in their application to the development of green photoredox catalytic methodologies. Accordingly, the present work explores their ability to promote the generation of both alkyl and acyl radicals starting from radical precursors such as Hantzsch esters, potassium alkyltrifluoroborates, and α-oxoacids. Mechanistic studies involving UV-visible absorption and fluorescence experiments, electrochemical measurements of the ground-state redox potentials along with computational calculations of both the ground- and the excited-state redox potentials of a set of nine different aromatic isocyanides provide key insights to promote a rationale design of a new generation of isocyanide-based organic photoredox catalysts. Importantly, the green potential of the investigated chemistry is demonstrated by a direct and easy access to deuterium labeled compounds.

Research on dye sensitized solar cells: recent advancement toward the various constituents of dye sensitized solar cells for efficiency enhancement and future prospects

It is universally accepted that the financial advancement of a state is essentially dependent upon the energy sector as it is essential in the growth, development, and improvement of the farming, mechanical, and defense sectors. A dependable source of energy is expected to enhance society's expectation of everyday comforts. Modern industrial advancement, which is indispensable for any nation, relies upon electricity. The principal explanation behind the energy emergency is rapidly increasing the use of hydrocarbon resources. Thus, the use of renewable resources is essential to overcome this dilemma. The consumption of hydrocarbon fuels and their discharge has destructive consequences on our surroundings. Third-generation photovoltaic (solar) cells are latest encouraging option in solar cells. Currently, dye-sensitized solar cells (DSSC) utilize organic (natural and synthetic) dye and inorganic (ruthenium) as a sensitizer. The nature of this dye combined with different variables has brought about a change in its use. Natural dyes are a feasible alternative in comparison to expensive and rare ruthenium dye owing to their low cast, easy utility, abundant supply of resources, and no environmental threat. In this review, the dyes generally utilized in DSSC are discussed. The DSSC criteria and components are explained, and the progress in inorganic and natural dyes is monitored. Scientists involved in this emerging technology will benefit from this examination.

Small Molecules Containing Amphoteric Imidazole Motifs as Sensitizers for Dye-Sensitized Solar Cells: An Overview

Organic dyes, porphyrins and inorganic complexes containing imidazole (IM) motifs have been demonstrated as a new class of sensitizers in dye-sensitized solar cells (DSSCs). Particularly, the amphoteric nature of IM-based motifs allows them to be used as donors (D), auxiliary donors (D_A), linker/branch (π), or acceptors (A) in D-π-A-based organic dyes and porphyrins and also employed as cyclometalated heteroleptic and ancillary ligands in the Ru(II) and Ir(III) complexes for DSSCs. It is noteworthy that the introduction of IM chromophores in the dyes of D-π-A configuration can improve the light-harvesting properties and prohibit the charge recombination reactions due to the extension of the π-conjugated structures and hydrophobic nature. Similarly, in the case of inorganic complexes, the presence of IM motifs as ligands can improve the light-harvesting ability, give facilely tuned HOMO and LUMO energy levels, increase the charge recombination resistance and photostability. This results in enhanced photocurrent (J_SC) and photovoltage (V_OC) and consequently solar-to-power conversion efficiency (η) of DSSC devices based on Ru(II) and Ir(III) complexes. Considering the interesting DSSC applications of IM-derived molecules, in this review, we therefore comprehensively discuss their photophysical, electrochemical and photovoltaic properties reported so far and establish their structure-activity relationship to further advance the η of DSSCs. To the best of our knowledge, there is no such a review interpreting the importance of molecules possessing IM-motifs for DSSC applications to date.

Effect of Iodide-Based Organic Salts and Ionic Liquid Additives in Dye-Sensitized Solar Cell Performance

The use of ionic liquid and organic salts as additives for electrolyte systems in dye-sensitized solar cells have been widely described in recent years. The tunability of their physical-chemical properties according to the cation-anion selection contributes toward their high efficiencies. For this purpose, several iodide-based organic salts including imidazolium, picolinium, guanidinium and alkylammonium cations were tested using acetonitrile/valeronitrile electrolytes and their photovoltaic parameters were compared. A best efficiency of 4.48% (4.15% for the reference) was found for 1-ethyl-2,3-dimethylimidazolium iodide ([C2DMIM]I) containing electrolyte, reaffirming the effectiveness of these additives. 4-tertbutylpyridine was included into the formulation to further improve the performance while determining which iodide salts demonstrate the highest synergy with this additive. [C2DMIM]I once again proved to be the superior additive, achieving an efficiency of 6.48% (6% for the reference). Electrochemical impedance spectroscopy was employed to elucidate the effects of the various additives, demonstrating the relevance of the counter electrode resistance on device performance. Finally, several computational descriptors for the cationic structures were calculated and correlated with the photovoltaic and resistance parameters, showing that properties related to polarity, namely relative positive charge, molecular polarizability and partition coefficient are in good agreement with the counter-electrode resistance.

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.

Improvements in photoelectric performance of dye-sensitised solar cells using ionic liquid-modified TiO2 electrodes

One of the major problems in dye-sensitised solar cells (DSSCs) is the aggregation of dyes on TiO₂ electrodes, which leads to undesirable electron transfer. Various anti-aggregation agents, such as deoxycholic acid, have been proposed and applied to prevent dye aggregation on the electrodes. In this study, we designed and synthesised a phosphonium-type ionic liquid that can be modified on the TiO₂ electrode surface and used as a new anti-aggregation agent. Although the modification of the ionic liquid onto the electrode reduced the amount of dye adsorbed on the electrode, it showed a significant anti-aggregation effect, thereby improving the photovoltaic performance of DSSCs with N3 and J13 dyes. This finding suggests that ionic liquids are effective as anti-aggregation agents for DSSCs.

The modification of the phosphonium-type ionic liquid onto the TiO₂ electrode reduced the amount of dye adsorbed on the electrode and showed significant aggregation effect, thereby improving the photovoltaic performance of DSSCs.

Synthetic Efforts to Investigate the Effect of Planarizing the Triarylamine Geometry in Dyes for Dye-Sensitized Solar Cells

The geometry of a dye for dye-sensitized solar cells (DSSCs) has a major impact on its optical and electronic properties. The dye structure also dictates the packing properties and how well the dye insulates the metal-oxide surface from oxidants in the electrolyte. The aim of this work is to investigate the effect of planarizing the geometry of the common triarylamine donor, frequently used in dyes for DSSC. Five novel dyes were designed and prepared; two employ conventional triarylamine donors with thiophene and furan π-spacers, two dyes have had their donors planarized through one sulfur bridge (making two distinct phenothiazine motifs), and the final dye has been planarized by forming a double phenoxazine. The synthesis of these model dyes proved to be quite challenging, and each required specially designed total syntheses. We demonstrate that the planarization of the triarylamine donor can have different effects. When planarization was achieved by a 3,7-phenothiazine and double phenoxazine structures, improved absorption properties were noted, and a panchromatic absorption was achieved by the latter. However, an incorrect linking of donor and acceptor moieties has the opposite effect. Further, electrochemical impedance spectroscopy revealed clear differences in charge recombination depending on the structure of the dye. A drawback of planarized dyes in relation to DSSC is their low oxidation potentials. The best photovoltaic performance was achieved by 3,7-phenothazine with furan as a π-spacer, which produces a power conversion efficiency of 5.2% (J _sc = 8.8 mA cm^-2, V _oc = 838 mV, FF = 0.70).

Effect of carboxylic acid and cyanoacrylic acid as anchoring groups on Coumarin 6 dye for dye-sensitized solar cells: DFT and TD-DFT study

Starting with Coumarin-6 dye, two novel D-π-A organic dyes C6X and C6N have been designed by attaching carboxylic acid and cyanoacrylic acid groups as anchoring groups to Coumarn-6 dye, respectively, to understand their potential use in dye-sensitized solar cells (DSSCs). The electronic structure and photophysical and photovoltaic properties of the novel designed dyes were studied using density functional theory DFT and time-dependent density functional theory TD-DFT with the Becke3-Parameter-Lee–Yang–Parr (B3LYP) functional and the 6-31G (d, p) basis set. Optimized structure and electronic properties (highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital (ELUMO), and energy difference (Eg) between HOMO and LUMO) were calculated showing that C6N has the smallest band gap with the larger absorption region. Density of states (DOS), molecular electrostatic potential (MEP), natural bond orbital (NBO) analysis, non-linear optical (NLO) properties, UV–vis spectra, as well as some crucial parameters affecting the photovoltaic performance of DSSCs, such as light-harvesting efficiency (LHE), electron injection driving force (ΔGinject), dye regeneration driving force(ΔGreg), and the excited state life time(τe), were calculated to study the effect of the anchoring group on the DSSC performance. Additionally, the adsorption of C6X and C6N dyes on the TiO2 anatase (101) surface and the mechanism of electron injection were also investigated using a dye–(TiO2)9 cluster model using TD-B3LYP calculation. The calculated adsorption energies of the dyes suggest a strong adsorption of dyes to a TiO2 surface. The results show that C6N may be theoretically a good candidate as sensitizer of DSSC application.

Ionic liquid dispersed highly conducting polymer electrolyte for supercapacitor application: Current scenario and prospects “ICSEM 2021”

Ionic liquid (IL) is now being considered as a novel contender in the development of highly conducting polymer electrolytes rather than a solvent. It has a significant impact on the electrochemical performance of polymer electrolytes. This study emphasizes the significance of low viscosity IL dispersion within a polymer (PVA) matrix. The electrical, structural and photoelectrochemical properties of the IL-doped polymer electrolyte are discussed in detail. These highly conducting IL doped solid polymer electrolytes show promise towards the development of highly efficient Supercapacitors.

Donor functionalized perylene and different π-spacer based sensitizers for dye-sensitized solar cell applications - a theoretical approach

A series of perylene-based novel metal-free organic dye sensitizers are designed and optimized for dye-sensitized solar cell (DSSC) applications. The electronic and optical properties are analyzed through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approach. For perylene-based donors, the effects of additional donor units and different π-spacer positions were investigated. Cyanovinyl and thiophene are used as π-spacers, dimethylamine (DM) and N-N-dimethylaniline (DMA) are used as additional donors, and cyanoacrylic acid is used as mono acceptor unit for the designed sensitizers. Natural bonding orbitals (NBOs), frontier molecular orbitals (FMO), UV-Vis, and nonlinear orbital analysis were predicted to find the net electron transfer, energy gap, absorption spectra, and electronic charge distribution for perylene-based dye sensitizers, respectively. The electron injection and electron regeneration properties were also analyzed for perylene-based sensitizers.

Characterizing Interfacial Structures of Dye-Sensitized Solar Cell Working Electrodes

In this feature article, we discuss the fundamental use of materials-characterization methods that directly determine structural information on the dye···TiO₂ interface in dye-sensitized solar cells (DSCs). This interface is usually buried within the DSC and submerged in solvent and electrolyte, which renders such metrological work nontrivial. We will show how ex-situ X-ray reflectometry (XRR), atomic-force microscopy (AFM), grazing-incidence X-ray scattering (GIXS), pair-distribution-function analysis of X-ray diffraction data (gaPDF), and in-situ neutron reflectometry (NR) can be used to deliver specific structural information on the dye···TiO₂ interface regarding dye anchoring, dye aggregation, molecular dye orientation, intermolecular spacing between dye molecules, interactions between the dye molecules and the TiO₂ surface, and interactions between the dye molecules and the electrolyte components and precursors. Some of these materials-characterization techniques have been developed specifically for this purpose. We will demonstrate how the direct acquisition of such information from materials-characterization experiments is crucial for assembling a holistic structural picture of this interface, which in turn can be used to develop DSC design guidelines. Moreover, we will show how these methodologies can be used in the experimental-validation process of "design-to-device" pipelines for big-data- and machine-learning-based materials discovery. We conclude with an outlook on further developments of this design-to-device approach as well as the materials characterization of more dye···TiO₂ interfacial structures that involve known DSC dyes using the methods described herein. In addition, we propose to combine these formally disparate metrologies so that their complementary merits can be exploited simultaneously. New metrologies of this kind could serve as a "one-stop-shop" for the materials characterization of surfaces, interfaces, and bulk structures in DSCs and other devices with layered architectures.

QSPR modeling of absorption maxima of dyes used in dye sensitized solar cells (DSSCs)

Dye-sensitized solar cells (DSSCs) have recently received a significant attention as possible sources of renewable energy. As a result, a significant effort is being made to develop organic dyes for highly power conversion efficient DSSCs, in order to overcome the disadvantages of previous solar cell systems, such as cost reduction, weight reduction, and production methods that minimize environmental pollution. As shown by multiple recent research publications, computational techniques such as quantitative structure-property relationship (QSPR) modeling may aid in the development of suitable dyes for DSSCs satisfying many fundamental desired characteristics. The current report provides robust, externally verified QSPR models for five chemical classes of organic dyes (Triphenylamines, Phenothiazines, Indolines, Porphyrins and Coumarins) based on experimentally determined absorption maxima values. The size of the dye data points utilized to develop the models is the largest known to date. The QSPR models were constructed using only two-dimensional descriptors with clear physicochemical meaning. Using the best subset selection approach, we built 5, 3, 4, 3 and 2 descriptor models for the Triphenylamine, Phenothiazine, Indoline, Porphyrin and Coumarin classes, respectively. The models were validated both internally and externally, and then consensus predictions were made for specific categories of dyes using the developed partial least squares (PLS) models, and the "Intelligent consensus predictor" tool (http://teqip.jdvu.ac.in/QSAR_Tools/) was used to determine whether the quality of test set compound predictions can be improved through the "intelligent" selection of multiple PLS models. We identified from the insights gained from the developed models several chemical attributes that are important in enhancing the absorption maxima. Thus, our study may be utilized to predict the λ_max values of novel or untested organic dyes and to give insights that will aid in the development of new dyes for use in solar cells with increased λ_max values and enhanced power conversion efficiency.

The Golden Fig: A Plasmonic Effect Study of Organic-Based Solar Cells

An optimization work on dye-sensitized solar cells (DSSCs) based on both artificial and natural dyes was carried out by a fine synthesis work embedding gold nanoparticles in a TiO₂ semiconductor and perfecting the TiO₂ particle sizes of the scattering layer. Noble metal nanostructures are known for the surface plasmon resonance peculiarity that reveals unique properties and has been implemented in several fields such as sensing, photocatalysis, optical antennas and PV devices. By embedding gold nanoparticles in the mesoporous TiO₂ layer and adding a scattering layer, we were able to boost the power conversion efficiency (PCE) to 10.8%, using an organic ruthenium complex. The same implementation was carried out using a natural dye, betalains, extracted from Sicilian prickly pear. In this case, the conversion efficiency doubled from 1 to 2% (measured at 1 SUN illumination, 100 mW/cm² under solar simulation irradiation). Moreover, we obtained (measured at 0.1 SUN, 10 mW/cm² under blue light LED irradiation) a record efficiency of 15% with the betalain-based dye, paving the way for indoor applications in organic natural devices. Finally, an attempt to scale up the system is shown, and a betalain-based- dye-sensitized solar module (DSSM), with an active area of 43.2 cm² and a PCE of 1.02%, was fabricated for the first time.

Toward Eco-Friendly Dye-Sensitized Solar Cells (DSSCs): Natural Dyes and Aqueous Electrolytes

Due to their low cost, facile fabrication, and high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have attracted much attention. Ruthenium (Ru) complex dyes and organic solvent-based electrolytes are typically used in high-efficiency DSSCs. However, Ru dyes are expensive and require a complex synthesis process. Organic solvents are toxic, environmentally hazardous, and explosive, and can cause leakage problems due to their low surface tension. This review summarizes and discusses previous works to replace them with natural dyes and water-based electrolytes to fabricate low-cost, safe, biocompatible, and environmentally friendly DSSCs. Although the performance of “eco-friendly DSSCs” remains less than 1%, continuous efforts to improve the PCE can accelerate the development of more practical devices, such as designing novel redox couples and photosensitizers, interfacial engineering of photoanodes and electrolytes, and biomimetic approaches inspired by natural systems.

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.

Synthesis and Physico-Chemical Properties of Homoleptic Copper(I) Complexes with Asymmetric Ligands as a DSSC Dye

To develop low-cost and efficient dye-sensitized solar cells (DSSCs), we designed and prepared three homoleptic Cu(I) complexes with asymmetric ligands, M1, M2, and Y3, which have the advantages of heteroleptic-type complexes and compensate for their synthetic challenges. The three copper(I) complexes were characterized by elemental analysis, UV-vis absorption spectroscopy, and electrochemical measurements. Their absorption spectra and orbital energies were evaluated and are discussed in the context of TD-DFT calculations. The complexes have high V_OC values (0.48, 0.60, and 0.66 V for M1, M2, and Y3, respectively) which are similar to previously reported copper(I) dyes with symmetric ligands, although their energy conversion efficiencies are relatively low (0.17, 0.64, and 2.66%, respectively).

Self-Assembled Materials Incorporating Functional Porphyrins and Carbon Nanoplatforms as Building Blocks for Photovoltaic Energy Applications

As a primary goal, this review highlights the role of supramolecular interactions in the assembly of new sustainable materials incorporating functional porphyrins and carbon nanoplatforms as building blocks for photovoltaics advancements.