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We provide a unified review of recent work carried out on computational investigations of a large series of Ru(II)–polypyridyl complexes effectively employed as solar cells sensitizers in dye-sensitized solar cells (DSCs). The use of methods rooted into Density Functional Theory (DFT) and its Time-Dependent extension (TDDFT) are demonstrated to be powerful tools to describe the electronic and optical properties of metallorganic ruthenium solar cells sensitizers, allowing us to unravel the interplay between their UV–Vis spectral changes and the complexes acid–base properties. This theoretical approach can be used to reproduce and understand the experimental data and also to design and predict the electronic and optical properties of new ruthenium-based sensitizer dyes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Extremely low efficiencies for β-carboxylated corroles in photovoltaic devices. [•] The carboxylic acid allows the adsorption on TiO2 and enhances the conjugation. [•] An unfavorable level alignment could be the cause of the low charge injection. [ABSTRACT FROM AUTHOR]

Abstract: We describe a theoretical investigation of a prototype β-elimination reaction in systems activated by the pyridine ring. The reactions investigated, the acetohydroxamic-induced and OH−-induced β-elimination with the nitrogen protonated N-[2-(2-pyridyl)ethyl]quinuclidinium substrate, offers a unique opportunity to test computational methodologies for the study of β-elimination reactions in solution since for this system detailed kinetic experimental data have been obtained. We calculated the pK as of the acetohydroxamic acid and of the substrate, for which experimental estimates are available. We then thoroughly characterized the reactive free-energy profile. Our study establishes that the reaction proceeds via a quasi reversible E1cb mechanism for the reaction induced by acetohydroxamate base, and irreversible E1cb mechanism for the reaction induce by OH− base, involving a stable carbanion intermediate. Except for a discrepancy in the reproduction of the pK a of the acetohydroxamic acid and of the H2O, the calculated free-energy profile is in excellent agreement with the experiment, showing the general reliability of the present approach. [Copyright &y& Elsevier]

Abstract: We present a combined experimental and computational density functional theory (DFT)/time-dependent DFT study of the geometry, electronic structure and optical absorption spectrum of the solar-cell sensitizers cis-[Ru(4,4′-COO−-2,2′-bpy)2(X)2]4− (X=NCS, Cl) in water solution. The experimentally observed red-shift of the spectrum upon substitution of NCS-by Cl-is well reproduced by our theoretical model and appears to be related to stabilization of the t2g–π∗ HOMOs in the NCS− complex. The π∗ LUMOs of the Cl complex are destabilized by a smaller extent with respect to the HOMOs, due to the increased π-back bonding interactions with the bipyridine ligands. [Copyright &y& Elsevier]

DFT/TDDFT calculations were performed to investigate the structural, electronic and optical properties of the [Ru(dppz)(phen)2]2+ complex in solution. TDDFT calculations in water show two groups of metal-to-ligand charge transfer (MLCT) transitions at ≈450 and 415 nm whose superposition gives account of the broad absorption band experimentally characterized at 440 nm. Also, a group of almost coincident MLCT transitions partially mixed with dppz intraligand π–π∗ transitions centered at ≈380 nm is found to give rise to the narrow absorption band experimentally found at 380 nm. Our results provide insight into the hypochromic shifts experimentally characterized upon intercalation of the title complex into DNA. [Copyright &y& Elsevier]

We present a combined density functional/time-dependent density functional study of the electronic structure and optical absorption spectrum of the charge-transfer sensitizer cis-[Ru(4,4′-COOH-2,2′-bpy)2(NCS)2] in water solution. To simulate the effect of different pH values, calculations have been performed for both the title complex and the corresponding tetra-deprotonated species, cis-[Ru(4,4′-COO-2,2′-bpy)2(NCS)2]4−. The experimentally observed blue-shift of the spectrum at high pH is well reproduced by our theoretical model and appears to be related to destabilization of the bipyridines π* LUMOs as a result of the increased electron density on the deprotonated carboxylic groups. [Copyright &y& Elsevier]

A theoretical investigation has been performed on the oxidative addition reaction pathway involved in the platinum-catalysed hydrosilylation of alkenes, analysing the oxidative addition of SiH4 to a platinum-diphosphine complex, Pt(PH3)2. Static and dynamic density functional calculations have been performed in order to investigate the reaction mechanism and dynamics of the oxidative addition reaction in the considered system. Our results indicate that the oxidative addition is both thermodynamically and kinetically favored and takes place via a reactant-like transition state leading directly to the more thermodynamically stable cis-[PtH(PH3)2–SiH3] square-planar product. [Copyright &y& Elsevier]

• Different Hamiltonian, basis sets and DFT functionals were compared. • Inclusion of the spin orbit coupling and Hartree Fock exchange is essential. • The Pb I bond has a partial covalent character. • PbI 2 and MAPbI 3 solid state materials can be treated with the same theoretical approach. A detailed knowledge of the basic electronic interactions in lead halide perovskites components (PbI 2 and methylammonium iodide) can possibly drive enhanced solar cell efficiency. We report an extensive investigation on the electronic structure and nature of the chemical bond in the PbI 2 perovskite precursor, both in gas and solid state, together with a comparison with available experimental data, which allows to effectively calibrate the computational framework, along with gaining basic understanding on the nature of the Pb I chemical bond. Inclusion of spin orbit coupling and calibrated HF exchange contribution to the DFT hybrid functional are proved essential for an accurate description of the electronic structure of both molecular and solid state PbI 2. Such computational framework, calibrated on the model PbI 2 system, can be directly translated to the accurate description of the electronic band structure of the prototypical methylammonium lead-iodide perovskite, setting the basis for the trustful modelling of different lead-halide perovskites. [ABSTRACT FROM AUTHOR]

[Display omitted] Indirect absorption extended below the direct transition edge and increase in carrier lifetime derived from Rashba spin–orbit coupling may advance the optoelectronic applications of metal halide perovskites. Spin-orbit coupling in halide perovskites is due to the presence of heavy elements in their structure. However, when these materials lack an inversion symmetry, for example by the application of strain, spin–orbit coupling becomes odd in the electron's momentum giving rise to a splitting in the electronic energy bands. Here we report on the observation of a large Rashba splitting of 117 meV at room temperature, as predicted by relativistic first-principles calculations, in halide perovskite single crystals through a facile compositional engineering approach. Partial substitution of organic cations by rubidium in single crystals induces significant indirect absorption and dual peak photoluminescence as a result of a large Rashba splitting. We measured circularly polarized photoluminescence and magneto-photoluminescence in perovskite films printed by single crystals as well as magneto-electroluminescence and magneto-photocurrent in spin-LEDs based on perovskite single crystals. They indicated significant spin-momentum locking due to the large Rashba effect. A hybrid perovskite single crystal photodetector achieved record figures of merit, including detectivity of more than 1.3 × 1018 Jones which represents a three orders of magnitude improvement compared to the to date record. These findings show that facile compositional engineering of perovskite single crystals holds great promise for further advancing the optoelectronic properties of existing materials. [ABSTRACT FROM AUTHOR]

A series of push–pull triarylamine organic dyes containing the benzo[1,2- b :4,5- b ′]dithiophene unit as a spacer and bearing alkyl chains in different positions of the molecule were synthesized. The new dyes 1 – 4 were characterized by optical and electrochemical measurements and density functional theory calculations and used as sensitizers in liquid dye-sensitized solar cells. The effect of alkyl chain position on dye properties and performances was investigated and dye 1 , bearing two 3,7-dimethyloctyl groups on the benzodithiophene core, exhibited the best behaviour in term of light absorption and cell performance (PCE of 6.6%, to be compared with a PCE of 8.1% for N719-based device). The efficiency of the DSSC was highly dependent on the solvent used for the dye-sensitizing bath, which affects the position of the COOH/COO − equilibrium. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical study is carried out on two novel carbazole-phenothiazine dyadic dyes bearing the simple carboxylic acid and the more rarely investigated malonic acid as anchoring group. An improvement of the photovoltaic performances is observed when the malonic acid is employed in place of the carboxylic acid, even if the highest efficiencies for this family of organic dyes were recorded with the use of the cyanoacrylic and rhodanine-3-aceti acid as anchoring units. The low photocurrents measured in the case of the carboxylic anchoring are rationalized on the basis of the computational modelling of the isolated dye in solution as well as the investigation of the electronic structure of extended dye-sensitized TiO 2 models. The theoretical calculations suggest that the low short current densities might arise from the unfavourable interplay of the dye's optical properties (blue shift of the absorption spectrum) and of the energy alignment between the dye's LUMO and the semiconductor conduction band edge, possibly causing an inefficient electron injection process. [ABSTRACT FROM AUTHOR]

We report a new class of multifunctional 9,10-dithienylanthracene-based materials having an anthracene π-core functionalized at the 9,10 positions with thienyl side-arms of different size and type of substitution. MW-assisted double direct arylation reaction is employed for the first time to synthesize the target molecules in one-step, organometallic free conditions, in only 5 min and yields up to 80% rather than by a multi-step Stille coupling taken as conventional reference approach. DFT calculations reveal a molecular conformation characterized by the thienyl rings orthogonal to the anthracene core. Nevertheless, despite the non-coplanar structure, all compounds exhibited highly crystalline cast films emitting blue light, with an extraordinary variability in morphology and hole mobility up to 8×10 −3 cm 2 V −1 s −1 . [ABSTRACT FROM AUTHOR]

Abstract: Three new sterically demanding unsymmetrical zinc phthalocyanines have been designed and synthesized as sensitizers for dye-sensitized solar cells. All three unsymmetrical phthalocyanines have been completely characterized by elemental analyses, mass spectrometry, FT-IR, 1H NMR, UV–Visible, and fluorescence (steady-state and life-time) spectroscopies as well as electrochemical methods. Photophysical properties (absorption, emission and redox properties) indicate that the LUMO of unsymmetrical phthalocyanines lies above the TiO2 conduction band and HOMO is below the redox electrolyte. The experimental results are supported by DFT/TD-DFT studies. Electrochemical and in-situ spectroelectrochemical studies suggest that the redox reactions belong to the macrocyclic ring-based electron transfer processes. All three unsymmetrical phthalocyanines were tested in DSSC using I−/I3 − redox electrolyte system. [Copyright &y& Elsevier]

Push–pull Zn(II)-porphyrinates have recently shown attracting performances as light harvesting systems in dye-sensitized solar cells (DSSCs). To fully exploit their intrinsically high efficiency it is important to finely tune their HOMO and LUMO levels, which can be achieved by proper choice of the push and pull substituents. Of course such target-oriented molecular design requires the availability of reliable relationships between molecular structure and electronic properties; therefore we have carried out a combined electrochemical, spectroscopic and computational investigation on a wide, systematic range of Zn(II)-porphyrinates 5,15 meso substituted with phenylethynyl linkers, including a first symmetric series carrying on the opposite terminals the same substituent (N(CH3)2, ⚊OCH3,⚊ COOCH3, ⚊COOH, ⚊NO2); and a second push–pull one, with the terminal positions carrying one donor and one acceptor group belonging to the series above. Moreover, two suitably modified porphyrins allowed evaluation of the effects of (i) the presence or absence of the phenyl group in the linker between the porphyrin core and the acceptor group, and (ii) the effect of perfluorination on the same phenyl group. A rationalization scheme is proposed encompassing the whole porphyrin set, affording inter alia interesting clues on the different localization of the redox centres and effective conjugation between the porphyrin core and the side chains as a function of the molecular design. [Copyright &y& Elsevier]

Abstract: A series of new π-conjugated organic dyes (HKK-BTZ1, HKK-BTZ2, HKK-BTZ3 and HKK-BTZ4), comprising triphenylamine (TPA) moieties as the electron donor and benzothiadiazole moieties as the electron acceptor/anchoring groups, was synthesized for the use in dye-sensitized solar cells (DSSCs). TPA units are bridged to benzothiadiazole with single(S), double(D) and triple bonds(T) in different derivatives. And HKK-BTZ1 was modified by introducing alkoxy group of TPA unit, because the bulky alkoxy group is a strong donating group for the more red shift and for reducing aggregation of dyes in TiO2 film. The structure-property relationship was investigated. Under standard global AM 1.5G illumination, a maximum photo-to-electron conversion efficiency of 7.30% was achieved with the DSSC based on dye HKK-BTZ4 (J SC =17.9mA/cm−2, V OC =0.62V, FF=0.66), while the Ru dye N719-sensitized DSSC showed an efficiency of 7.82% with a J SC of 17.5mA/cm−2, a V OC of 0.62V, and a FF of 0.72. [Copyright &y& Elsevier]

Abstract: A series of coumarin dyes containing a low-band-gap chromophore of ethylenedioxythiophene (EDOT), which comprises a coumarin moiety as the electron donor and a cyanoacrylic acid moiety as electron acceptor in D–π–A chromophores, were developed for use in dye-sensitised solar cells (DSSCs). These coumarin dyes have been used to fabricate DSSCs using I−/I3 − liquid electrolytes and their device performances were compared with that of NKX-2677 as a standard dye. Even though HKK-CM2 and HKK-CM3 have more extended aromatic units than HKK-CM1, the degree of π-conjugation in HKK-CM2 and HKK-CM3 is less efficient than that of HKK-CM1, due to the relatively larger torsion angle between the plane of the donor and that of the acceptor. It is also in a good agreement with Density Functional Theory (DFT) calculations. As a result, a solar cell based on HKK-CM1 sensitiser shows better photovoltaic performance with JSC of 14.2 mA cm−2, VOC of 0.60 V, and a fill factor of 0.70, corresponding to an overall conversion efficiency η of 6.07% under the standard AM 1.5 irradiation, than HKK-CM2 and HKK-CM3-based solar cells. [Copyright &y& Elsevier]

Abstract: [Ir(cyclometallated 4,5-diphenyl-2-methyl-thiazole)2(5-R-1,10-phenanthroline)][PF6] (R=CH3, NO2) complexes were prepared and fully characterized, the structure of the complex with 5-CH3-1,10-phenanthroline being also determined by X-ray diffraction. The emission properties of both complexes have been investigated and their second-order nonlinear optical (NLO) response has been determined experimentally by the EFISH technique and found to be similar but slightly lower than that of related [Ir(ppy)2(5-R-1,10-phenanthroline)][PF6] (ppy=cyclometallated 2-phenylpyridine), characterized by one of the highest second-order NLO response ever reported for a metal complex. In the complexes, SOS/TDDFT calculations show that the large and negative sign of the measured hyperpolarizability is mainly due to the significant contribution of rather intense MLCT transitions involving the phenanthroline as acceptor ligand. [Copyright &y& Elsevier]