Organic Dyes Containing Coplanar Diphenyl-Substituted Dithienosilole Core for Efficient Dye-Sensitized Solar Cells

A theoretical study of the ligand-controlled palladium-catalysed regiodivergent synthesis of dibenzosilepin derivatives

Palladium-catalysed ligand-controlled 1,n-palladium migration of silicon-tethering substrates provides a regiodivergent synthesis strategy for constructing silicon-bridged π-conjugated compounds possessing a 6,6-fused or a 5,7-fused scaffold. Density functional theory (DFT) calculations were carried out to elucidate the detailed mechanism of this 1,n-palladium migration involving syn- or anti-carbopalladation. The computational results suggest that alkyne insertion is the regioselectivity-determining step. Upon catalysis without the BINAP ligand, the 1,2-insertion of an alkyne into the Pd-aryl bond leads to the formation of 6,6-fused benzophenanthrosiline, which is more favorable than the 2,1-insertion of alkyne by 4.2 kcal mol^-1. The selective formation of 5,7-fused benzofluorenosilepins via the 2,1-alkyne insertion is facilitated by the BINAP ligand. The 1,2-alkyne insertion with the BINAP ligand is disfavoured due to the steric repulsion between the phenyl group of the substrate and the naphthalene group of the BINAP ligand. The 2,1-alkyne insertion with the BINAP ligand orients the ligand away from the phenyl group of the substrate, which can avoid steric repulsion.

Theoretical Investigation on Photophysical Properties of Triphenylamine and Coumarin Dyes

Organic molecules with donor and acceptor configures are widely used in optoelectronic materials. Triphenylamine dyes (TPCTh and TPCRh) are investigated via density functional theory (DFT) and time-dependent DFT. Some microscopic parameters related to light absorption and photoelectric formation are calculated to interpret the experimental performance in dye-sensitized solar cells (DSSCS). Considering that coumarin derivatives (Dye 10 and Dye 11) have good donor and acceptor structures, they also have a COOH group used as an anchoring group to connect with semiconductors. Thus, the two dyes' photophysical and photoelectric properties are analyzed to estimate the performance and application in DSSCs.

Theoretical study of D-A'-π-A/D-π-A'-π-A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells

We have designed four dyes based on D-A'-π-A/D-π-A'-π-A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO-LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting efficiency (LHE), hole-electron distribution, charge transfer amount from HOMO to LUMO (Q CT), D index, H CT index, S m index and exciton binding energy (E coul) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D-π-A'-π-A configuration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.

Prediction of Absorption Spectrum Shifts in Dyes Adsorbed on Titania

Dye adsorption on metal-oxide films often results in small to substantial absorption shifts relative to the solution phase, with undesirable consequences for the performance of dye-sensitized solar cells and optical sensors. While density functional theory is frequently used to model such behaviour, it is too time-consuming for rapid assessment. In this paper, we explore the use of supervised machine learning to predict whether dye adsorption on titania is likely to induce a change in its absorption characteristics. The physicochemical features of each dye were encoded as a numeric vector whose elements are the counts of molecular fragments and topological indices. Various classification models were subsequently trained to predict the type of absorption shift i.e. blue, red or unchanged (|Δλ| ≤ 10 nm). The models were able to predict the nature of the shift with a good likelihood (~80%) of success when applied to unseen data.

Direct comparison of dithienosilole and dithienogermole as π-conjugated linkers in photosensitizers for dye-sensitized solar cells

Dithienosilole (DTS) and dithienogermole (DTG) are useful building units of π-conjugated organic materials. In the present work, donor-π-acceptor (D-π-A) dyes with bis(dihexyloxyphenyl)aminophenyl, DTS or DTG, and pyridine or cyanoacrylic acid as the donor (D), the π-conjugated linker (π), and the acceptor (A) units, respectively, were prepared and their optical properties were investigated. The D-π-A dyes exhibited strong absorption in the visible region, indicating efficient intramolecular donor-acceptor interaction. The addition of trifluoroacetic acid to solutions of pyridine-containing dyes led to red-shifts of the absorption bands as a result of pyridinium salt formation. Similar red-shifts were observed for cyanoacrylic acid dyes, which were due to the enhanced formation of neutral dyes relative to the separated ion pairs. The D-π-A dyes, however, showed similar absorption spectra when attached to the TiO2 surface, indicating that the dye-TiO2 electronic interaction was rather weak. In contrast to the finding that these dyes exhibited similar optical properties regardless of the π-linker (i.e., DTS or DTG), dye-sensitized solar cells (DSSCs) based on DTG-containing dyes exhibited superior performance compared to those based on DTS-containing dyes. Electrochemical impedance spectroscopy measurements supported the higher performance of the DSSCs with DTG-containing dyes.

Chemisorption of Atomically Precise 42-Carbon Graphene Quantum Dots on Metal Oxide Films Greatly Accelerates Interfacial Electron Transfer

Graphene quantum dots (GQDs) are emerging as environmentally friendly, low-cost, and highly tunable building blocks in solar energy conversion architectures, such as solar (fuel) cells. Specifically, GQDs constitute a promising alternative for organometallic dyes in sensitized oxide systems. Current sensitized solar cells employing atomically precise GQDs are based on physisorbed sensitizers, with typically limited efficiencies. Chemisorption has been pointed out as a solution to boost photoconversion efficiencies, by allowing improved control over sensitizer surface coverage and sensitizer-oxide coupling strength. Here, employing time-resolved THz spectroscopy, we demonstrate that chemisorption of atomically precise C42-GQDs (hexa- peri-hexabenzocoronene derivatives consisting of 42 sp² carbon atoms) onto mesoporous metal oxides, enabled by their functionalization with a carboxylate group, enhances electron transfer (ET) rates by almost 2 orders of magnitude when compared with physisorbed sensitizers. Density functional theory (DFT) calculations, absorption spectroscopy and valence band X-ray photoelectron spectroscopy reveal that the enhanced ET rates can be traced to stronger donor-acceptor coupling strength enabled by chemisorption.

Synthesis of dipyrrolopyrazine-based sensitizers with a new π-bridge end-capped donor–acceptor framework for DSSCs: a combined experimental and theoretical investigation

Organic dyes with dipyrrolopyrazine as the central π-linker have been synthesized. Photovoltaic properties were investigated and supported by DFT. Thermal analysis shows good thermal stability.

Effect of donor modification on the photo-physical and photo-voltaic properties of N-alkyl/aryl amine based chromophores

Six push–pull sensitizers (MD1 to MD6) having rhodanine-3-acetic acid acting as an electron withdrawing group and N-alkyl/aryl amine as a donor moiety were planned and prepared to rationalize the influence of donor alteration on absorption/emission properties and photon to current conversion efficiency (η).

Structure-efficiency relationship of newly synthesized 4-substituted donor–π–acceptor coumarins for dye-sensitized solar cells

Substitution at the 4-position of coumarin alters the photophysical, electrochemical and photovoltaic properties of the dyes.

Molecular design towards suppressing electron recombination and enhancing the light-absorbing ability of dyes for use in sensitized solar cells: a theoretical investigation

We report a molecular design strategy with a comprehensive consideration of both inhibiting electron recombination and enhancing the light-harvesting ability.

Hybrid conjugated polymers with alternating dithienosilole or dithienogermole and tricoordinate boron units

Hybrid conjugated polymers with alternating dithienosilole or dithienogermole and tricoordinate boron units were prepared, which showed effective D–A interactions.

Improvement of Transparent Conducting Performance on Oxygen-Activated Fluorine-Doped Tin Oxide Electrodes Formed by Horizontal Ultrasonic Spray Pyrolysis Deposition

In this study, highly transparent conducting fluorine-doped tin oxide (FTO) electrodes were fabricated using the horizontal ultrasonic spray pyrolysis deposition. In order to improve their transparent conducting performances, we carried out oxygen activation by adjusting the ratio of O₂/(O₂+N₂) in the carrier gas (0%, 20%, and 50%) used during the deposition process. The oxygen activation on the FTO electrodes accelerated the substitution concentration of F (F_O^•) into the oxygen sites in the FTO electrode while the oxygen vacancy (V_O^••) concentration was reduced. In addition, due to growth of pyramid-shaped crystallites with (200) preferred orientations, this oxygen activation caused the formation of a uniform surface structure. As a result, compared to others, the FTO electrode prepared at 50% O₂ showed excellent electrical and optical properties (sheet resistance of ∼4.0 ± 0.14 Ω/□, optical transmittance of ∼85.3%, and figure of merit of ∼5.09 ± 0.19 × 10^-2 Ω^-1). This led to a superb photoconversion efficiency (∼7.03 ± 0.20%) as a result of the improved short-circuit current density. The photovoltaic performance improvement can be defined by the decreased sheet resistance of FTO used as a transparent conducting electrode in dye-sensitized solar cells (DSSCs), which is due to the combined effect of the high carrier concentration by the improved F_O^• concentration on the FTO electrodes and the fasted Hall mobility by the formation of a uniform FTO surface structure and distortion relaxation on the FTO lattices resulting from the reduced V_O^••• concentration.

Broad-absorbing tetrabenzocorrolazine green photosensitizer for the enhanced conversion efficiency in dye-sensitized solar cells

Novel tetrabenzocorrolazine green photosensitizer was designed and synthesized to enhance the solar energy-to-electricity conversion efficiency of dye-sensitized solar cells. This near-infrared absorbing dye exhibited superior short-circuit photocurrent density induced from the additional absorption compared to the phthalocyanine dye commonly applied as a photosensitizer covering the near-infrared region in dye-sensitized solar cells. The introduction of bulky peripheral groups and axial substituents to the novel dye led to the increase of open-circuit photovoltage. As a result, the novel tetrabenzocorrolazine dye achieved a solar energy-to-electricity conversion efficiency of 3.78% under AM 1.5G conditions which was much higher than that of the phthalocyanine reference dye.

Synthesis of organic photosensitizers containing dithienogermole and thiadiazolo[3,4-c]pyridine units for dye-sensitized solar cells

Three dithienogermole-containing dyes were prepared and applied to dye-sensitized solar cells.

Effect of π-spacers and anchoring groups on the photovoltaic performances of ullazine-based dyes

Three ullazine-based organic sensitizers were designed, synthesized and applied in dye-sensitized solar cells (DSSCs). The tuning of π-spacers and anchoring groups led to a variation of the photovoltaic performances.

Push–pull type alkoxy-wrapped N-annulated perylenes for dye-sensitized solar cells

Three push–pull type, alkoxy-wrapped N-annulated perylene based sensitizers were synthesized and power conversion efficiency up to 8.38% was achieved.

Porphyrin Sensitizers Bearing a Pyridine-Type Anchoring Group for Dye-Sensitized Solar Cells

Three novel efficient donor-acceptor porphyrins, MH1-MH3, with a pyridine-type acceptor and anchoring group were synthesized and their optical, electrochemical, and photovoltaic properties investigated. Replacing the commonly used 4-carboxyphenyl anchoring group with 2-carboxypyridine, 2-pyridone, and pyridine did not significantly change the absorption and electrochemical properties of the porphyrin dyes. These new porphyrin dyes MH show power conversion efficiencies of 8.3%, 8.5%, and 8.2%, which are comparable to that of the benchmark YD2-o-C8 (η=8.25%) under similar conditions. It was demonstrated that 2-carboxypyridine is an efficient and stable anchoring group as MH1 and showed better cell performance and long-term stability than YD2-o-C8 under light soaking conditions.

Application and recognition behaviors of TPA-cored probes with subtle structural change

Two new triphenylamine-cored probes (L1, L2) with different receptor units have been synthesized and fully characterized by IR, NMR and MS spectra. Their photophysical properties have been investigated in detail. The recognition abilities of two probes were evaluated by a series of metal ions, which showed that L1 could recognize Cu(2+) over other metal ions. L2 could respond to Cu(2+), Hg(2+) in a short time, which interferes with a little each other. The Job's plot and (1)H NMR titration of L1 with Cu(2+) and L2 with Cu(2+) (Hg(2+)) in CD3CN verified the coordination mode of complexes L1-Cu(2+), L2-Cu(2+) and L2-Hg(2+), respectively. The limit of detection of L2 for Cu(2+) was lower than that of L1 towards Cu(2+). The results demonstrated that the receptor units in the probes had remarkable effect on recognizing metal ions. Meanwhile, L1 and L2 showed potential application in bio-imaging after mixing with Cu(2+).

N-Annulated perylene-based metal-free organic sensitizers for dye-sensitized solar cells

A series of novel metal-free organic sensitizers based on N-annulated perylene derivatives have been conveniently synthesized, and the DSCs exhibit overall conversion efficiencies ranging from 4.90% to 8.28%.

Improvement of dye-sensitized solar cells performance through introducing different heterocyclic groups to triarylamine dyes

The overall power conversion efficiency (PCE) of DSSCs based on TTR1–3 with chenodeoxycholic acid (CDCA) coadsorbant are 5.20%, 5.71% and 6.30%, respectively, and the value of TTR3 is close to that of N719 (6.62%).