Effect of number and position of methoxy substituents on fine-tuning the electronic structures and photophysical properties of designed carbazole-based hole-transporting materials for perovskite solar cells: DFT calculations

Dopant-Free Spiro-OMe2 Imidazole-Based Hole-Transporting Material for Stable and Low-Cost Organic-Inorganic Perovskite Solar Cell

The engineering of charge transport materials, with electronic characteristics that result in effective charge extraction and transport dynamics, is pivotal for the realization of efficient perovskite solar cells (PSCs). Herein, we elucidate the critical role of terminal substituent methoxy groups (-OCH3) on the bandgap tuning of the spiro-like hole transport materials (HTMs) to realize performant and cost-effective PSCs. By considering spiro-OMeTAD as the benchmark HTM, we kept the backbone of spiro while replacing diphenylamine with phenanthrenimidazole. This approach significantly decreases the cost of spiro-OMeTAD by reducing the cost of the ancillary group from 0.051 to 0.012 $/g. By increasing the number of methoxy groups on the ancillary ligand from four to eight, the power conversion efficiency (PCE) of the corresponding PSCs containing dopants passed from 17.10% to 18.70%, approaching the value achieved using spiro-OMeTAD containing dopants (PCE = 19.26%). Remarkably, the devices based on dopant-free spiro-OMeTAD have shown a significant loss of PCE, which decreased from 12.9% to 10.1% after 300 h (to 8.2% after 600 h) of light soaking at an open circuit voltage. On the contrary, the cells based on the designed dopant-free HTM demonstrated optimal PCE retention, experiencing a minor drop from 14.4% to 14.1% and 13.2% after 300 and 600 h, respectively, of light soaking at open-circuit voltage.

Synthesis, Photophysical Properties, Theoretical Studies, and Living Cancer Cell Imaging Applications of New 7-(Diethylamino)quinolone Chalcones

In this article, three unsymmetrical 7-(diethylamino)quinolone chalcones with D-π-A-D and D-π-A-π-D type push-pull molecular arrangements were synthesized via a Claisen-Schmidt reaction. Using 7-(diethylamino)quinolone and vanillin as electron donor (D) moieties, these were linked together through the α,β-unsaturated carbonyl system acting as a linker and an electron acceptor (A). The photophysical properties were studied, revealing significant Stokes shifts and strong solvatofluorochromism caused by the ICT and TICT behavior produced by the push-pull effect. Moreover, quenching caused by the population of the TICT state in THF-H2O mixtures was observed, and the emission in the solid state evidenced a red shift compared to the emission in solution. These findings were corroborated by density functional theory (DFT) calculations employing the wb97xd/6-311G(d,p) method. The cytotoxic activity of the synthesized compounds was assessed on BHK-21, PC3, and LNCaP cell lines, revealing moderate activity across all compounds. Notably, compound 5b exhibited the highest activity against LNCaP cells, with an LC50 value of 10.89 μM. Furthermore, the compounds were evaluated for their potential as imaging agents in living prostate cells. The results demonstrated their favorable cell permeability and strong emission at 488 nm, positioning them as promising candidates for cancer cell imaging applications.

Diphenylamine-based hole-transporting materials for excessive-overall performance perovskite solar cells: Insights from DFT calculations

Density functional theory calculations were employed to identify the ability of some diphenylamine-based hole-transporting materials (HTMs) for use in top-performance perovskite solar cells. The effects of donor/acceptor electron groups and the new π-bridge section in the three-part of structures were investigated thoroughly. The results indicated that adding electron-withdrawing functional groups such as CN in the phenylazo-indol moiety and substituting electron donor groups such as CH3 in the NH2 hydrogen atoms of the diphenylamine section can cause higher power conversion light-harvesting efficiency in new HTMs. Also, the replacement of thieno [3,2-b] benzothiophene as a part of the π bridge with the phenyl group according to the optical and electronic structure properties improves the efficiency of the new phenylazoindole derivatives.

Theoretical analysis on D-π-A triphenylamine-based dyes for dye-sensitized solar cells: effect of π-bridges on the optoelectronic, and photovoltaic properties

CONTEXT

The dye-sensitized solar cell is a technology unique in its light conversion properties as it operates with record efficiencies in diffused light conditions. The choice of the appropriate sensitizer is one of the important strategies to improve photovoltaic performance of DSSC devices. This theoretical study mainly aims to determine the impact of the π-spacer on the geometric and optoelectronic parameters of sensitizer dyes. For that, we have chosen six organic dyes of Donor-π-Acceptor structure based on triphenylamine unit as electron donor, cyanoacrylic acid as electron acceptor with various π-bridges. The results indicated that the doping process modify dihedral angles and electronic properties by enhancing the planarity and decreasing the gap energy. We have examined the optoelectronic and photovoltaic properties of studied triphenylamine based-dyes. Introducing thiophene and furan as π-spacer groups in D6 dye can effectively decrease the gap energy (E_gap = 2.21 eV), broaden the absorption range (λ_max = 671.19 nm), and promote the light-harvesting properties. The D2 dye based on two pyrrole units presents an improved electron injection driving force (ΔG^inject = - 2.269 eV) and regeneration driving force corresponding to better charge separation. The π-bridge groups can efficiently tune the optoelectronic and photovoltaic properties of sensitizers, which contribute to the efficiency of solar cells.

METHODS

The geometrical and electronic properties of all systems were studied by the DFT method using the correlation exchange functional B3LYP combined with 6-31G(d, p) basis set. On the other hand, the maximum absorption wavelengths λ_max and the corresponding oscillator strengths were calculated using the hybrid functional BHandHLYP and 6-31+G(d) basis set. The solvent tetrahydrofuran (THF) are used to study the effect of the solvent, using the "Conductor-Polarizable Continuum" (C-PCM) model. All calculations were performed using Gaussian 09 program.

Experimental study on fracture characteristics of rock-like material with prefabricated cracks under compression shear

In order to understand the effects of different patterns of prefabricated fractures and grain size compositions on the fracture characteristics, acoustic emission characteristics and mechanical properties of the rock masses. We conducted compression shear experiments on square rock masses with different modes of prefabricated fractures and different grain size compositions. The experimental results showed that five fracture patterns were produced in specimens with different fracture patterns. The first fracture specimen, the fourth fracture specimen and the fifth fracture specimen were all brittle fractures. The other four specimens were not brittle fractures. The fracture patterns, fracture processes and mechanical characteristics of the different fracture pattern rock masses were revealed. The lowest peak shear stresses were found in specimens consisting of two grain size ranges and the highest peak shear stresses were found in specimens consisting of three grain size ranges. The highest shear displacements corresponding to the peak shear stresses were found in the specimens consisting of three particle size ranges. The effect of different grain size compositions on the peak shear stress and its corresponding shear displacement of the rock mass was revealed. Specimens consisting of one grain size range produced significant fracture and acoustic emission prior to the peak shear stress. The acoustic emission was jumped after the main fracture was formed. The specimen consisting of two grain size ranges produced fractures and strong acoustic emission characteristics after the peak shear stress. Thereafter, fracture reappeared and the acoustic emission signature increased again. As the specimen entered the residual strength phase, the acoustic emission was jumpy. Specimens consisting of three grain size ranges were brittle fractures with weak acoustic emission characteristics after the main fracture has formed. The cumulative energy of shear acoustic emission was the highest for a rock mass consisting of three grain size ranges. The rock mass consisting of three grain size ranges was also the strongest and most difficult to fracture because the grains were more fully embedded in each other.

Butterfly-Like Triarylamines with High Hole Mobility and On/Off Ratio in Bottom-Gated OFETs

Highly π-extended butterfly-shaped triarylamine dyads with aryleneethynylene spacer were constructed using an efficient synthetic route. These aryleneethynylene-bridged dyads are highly fluorescent and exhibited high HOMO levels, and low bandgaps, which are suitable for high-performance p-type OFETs. The field-effect transistors were fabricated through a solution-processable method and exhibited promising p-type performance with field-effect mobility up to 4.3 cm² /Vs and high I_on/off of 10⁸ under ambient conditions.

Benchmark calculations of proton affinity and gas-phase basicity using multilevel (G4 and G3B3), B3LYP and MP2 computational methods of para-substituted benzaldehyde compounds

This study presents the benchmark calculations of proton affinities (PAs) and gas-phase basicities (GBs) of 8-para substituted benzaldehyde compounds using the multilevel model chemistries (G3B3 and G4), density-functional quantum model (B3LYP) and ab initio model (MP2). The results show that the computed properties are strongly correlated with the available experimental data. The PAs and the GBs of other eight para-substituted benzaldehyde compounds, for which the experimental data does not currently exist, have been calculated using G3B3 and B3LYP methods. The correlations between the experimental PAs and GBs with the computed properties such as PA, GB, chemical properties (bond lengths, electron density and δ¹ H NMR chemical shift) of the investigated benzaldehydes have been studied and statistically analyzed. The influence of the substituted groups has been discussed in terms of inductive effect and electron donating and electron withdrawing effect. The results obtained show that the chemical properties of the benzaldehyde compounds are controlled by the strong coupling between the CHO group and the nature of the para-substituent groups through the benzene ring as a conducting linkage.

Functional Pyrene-Pyridine-Integrated Hole-Transporting Materials for Solution-Processed OLEDs with Reduced Efficiency Roll-Off

A series of new functional pyridine-appended pyrene derivatives, viz., 2,6-diphenyl-4-(pyren-1-yl)pyridine (Py-03), 2,6-bis(4-methoxyphenyl)-4-(pyren-1-yl)pyridine (Py-MeO), 4-(pyren-1-yl)-2,6-di-p-tolylpyridine (Py-Me), and 2,6-bis(4-bromophenyl)-4-(pyren-1-yl)pyridine (Py-Br) were designed, developed, and studied as the hole-transporting materials (HTMs) for organic light-emitting diode (OLED) application. The crystal structures of two molecules revealed to have a large dihedral angle between the pyrene and pyridine units, indicating poor π-electronic communication between them due to ineffective orbital overlap across the pyrene-pyridine systems as the two p-orbitals of pivotal atoms are twisted at 66.80° and 68.75° angles to each other in Py-03 and Py-Me, respectively. The influence of variedly functionalized pyridine units on the electro-optical properties and device performance of the present integrated system for OLED application was investigated. All of the materials have suitable HOMO values (5.6 eV) for hole injection by closely matching the HOMOs of indium tin oxide (ITO) and the light-emitting layer. All of the synthesized molecules have suitable triplet energies, glass transition temperatures, and melting temperatures, which are highly desirable for good HTMs. The pyrene-pyridine-based devices demonstrated stable performance with low-efficiency roll-off. The device with Py-Br as HTM showed a maximum luminance of 17300 cd/m² with a maximum current efficiency of 22.4 cd/A and an EQE of 9% at 3500 cd/m² with 7% roll-off from 1000 to 10 000 cd/m². Also, the devices with Py-Me and Py-03 showed performance roll-up while moving from 1000 to 10 000 cd/m².

Single- and co-sensitization of triphenylamine-based and asymmetrical squaraine dyes on the anatase (001) surface for DSSC applications: Periodic DFT calculations

Dye aggregation causes poor performance of dye-sensitized solar cell (DSSC) applications through faster charge recombination of the photosensitizer with electrolyte. Triphenylamine (TBA)-based dyes feature a higher molar absorption coefficient and broadened wavelength but cannot absorb sunlight in the near-infrared (NIR) region. In contrast, the squaraine (SQ) photosensitizer, which is also called an NIR photosensitizer, has a maximum wavelength in the NIR region with high intensity. However, SQ dye suffers from dye aggregation due to its planar structure. The use of a co-sensitizer is one well-tested way to increase the power conversion efficiency (η) of solar cells by reducing dye aggregation and charge recombination. Using density functional theory (DFT) and time-dependent DFT (TDDFT), this work explains from a theoretical perspective the higher η values of the TZC1 and TZC2 dyes compared to that of asymmetric the SQ sensitizer (YR6) as free dyes. The electronic properties, reorganization energies, absorption and emission spectra, ICT parameters, and photovoltage parameters of the TZC1, TZC2, and YR6 dyes were computed using the M06/6-31G(d,p) level of theory in the gas phase and CH₂Cl₂ solvent (CPCM method). Additionally, the mono- and co-adsorption processes of TZC-based sensitizers with YR6 on the anatase (001) surface were investigated using periodic DFT calculations with the PBE + U/PAW method and the dispersion correction of the Grimme method D3. The results reveal that the use of the co-sensitized led to significant stabilization of the formed complexes by at least 1.21 eV, the panchromatic effect on the absorption spectra, and an increase in the light-harvesting ability in the NIR region, which improves the performance of DSSCs.

Simple 3,6-disubstituted Carbazoles as Potential Hole Transport Materials: Photophysical, Electrochemical and Theoretical Studies

Developing effective and low-cost organic hole-transporting materials (HTMs) is crucial for the construction of high-performance perovskite solar cells (PSCs) and to promote their production in commercial ventures. In this context, we herein report the molecular design, synthesis and characterization of two novel D-A-D-A-D architectured 9-(2-ethylhexyl)-9H-carbazoles, connecting the mono/dimethoxyphenyl substituted cyanovinylene sidearms symmetrically at 3^rd and 6^th positions of the carbazole heterocycle (CZ_1-2 ), as potential hole-transporting materials (HTMs). The current work highlights their structural, photophysical, thermal, electrochemical and theoretical investigations, including their structure-property correlation studies. Evidently, the optical studies showcased their excellent fluorescence ability due to their push-pull natured structure with extended π-conjugation. Further, in-depth solvatochromic studies demonstrated their intramolecular charge-transfer (ICT)-dominated optoelectronic behavior, supported by various correlation studies. Also, the optical results revealed that CZ₁  and CZ₂ display λ_abs  and λ_emi  in the order of 410-430 nm and 530-560 nm, respectively, with a bandgap in the range of 2.5-2.6 eV. Finally, their quantum chemical simulations have provided an insight into the predictions of their structural, molecular, electronic and optical parameters. Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of carbazole-based HTMs for achieving better performance.