Passivating Defects of Perovskite Solar Cells with Functional Donor-Acceptor–Donor Type Hole Transporting Materials

In this study, a series of donor–acceptor–donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.     

Diphenylamino-substituted derivatives of 9-phenylcarbazole as glass-forming hole-transporting materials for solid state dye sensitized solar cells

The synthesis and properties of glass-forming diphenylamino-substituted derivatives of 9-phenylcarbazole with methoxy groups in the different position of diphenylamino moieties are reported. A comparative study on their thermal, optical, photoelectrical and electrochemical properties is presented. The synthesized compounds exhibit high thermal stability with 5% weight loss temperatures ranging from 344 to 475 °C. The derivatives absorb electromagnetic irradiation in the range of 225–425 nm with the band gaps of 2.94–3.08 eV. The ionization energies of the synthesized compounds range from 5.04 to 5.56 eV. The lowest ionization energies and band gaps are observed for compounds containing para methoxy-substituted phenyl rings of diphenylamino moieties and for disubstituted carbazole derivatives. Charge-transporting properties of the selected compounds were tested by time-of-flight technique. Hole drift mobilities in the amorphous layers of the materials reach 10⁻³ cm²/V s at high electric fields. The derivatives were tested as hole transport materials in solid-state dye sensitized solar cells and showed conversion efficiency up to 0.54%.     

Estimating stresses and movement work of a soil-cultivator tip using the finite-element method

Working parts of tillage machines are in direct contact with soil abrasives. The shape and dimensions of the working parts undergo changes due to friction and wear. A finite-element model has been created for studying the stresses and in-soil movement work of the designed cultivator tip. The problem has been solved with a coupled Eulerian–Lagrangian method (the SIMULIA ABAQUS software). It has been shown that the minimum in-soil movement work of 3400 J is done by a tip with a sharpening angle of 185°.     

Simulations of the working contact loads of a tillage element

It has been suggested that the wear characteristics of a cultivator tip during tillage and a finite-element model based on the combination of the Euler and Lagrange methods be studied. The results of simulations show that surfaces with the largest contact loads correspond to the surfaces with greatest wear. It has been noted that the lower point of the front edge at a cultivator tip is under the action of the greatest contact load (120 N).     

Structure–properties relationship of hydrazones containing methoxy-substituted triphenylamino groups

We have synthesized a series of hole-transporting dimethoxytriphenylamine-based hydrazones and studied the influence of the position of methoxy groups on the thermal, optical, electrochemical, and photoelectrical properties of the materials. The synthesized compounds form glasses with glass transition temperatures ranging from 32 to 64 °C. Compounds having methoxy groups in the ortho positions of triphenylamino moiety show higher glass transition temperatures than the corresponding derivatives having methoxy substituents in meta or para positions. Ionization potentials of the solid samples of hydrazones range from 5.18 to 5.27 eV. Hydrazones having methoxy substituents in para positions of triphenylamino moiety show superior charge-transporting properties with respect to hydrazones containing methoxy substituents in ortho and meta positions respectively. Molecularly doped bisphenol Z polycarbonate containing 50 wt.% of hydrazones with methoxy substituents in para positions of triphenylamino moiety show time-of-flight hole-drift mobilities approaching 10^?4 cm²/(V s) at high electric fields.     

N-(2,2-Diphenylvinyl)-N,N′-diphenylbenzidine-based derivatives as hole-transporting glass-forming materials

Several N-(2,2-diphenylvinyl)-N,N′-diphenylbenzidine-based derivatives were synthesized by the multi-step synthetic route. Full characterization of their structure is presented. The synthesized materials were examined by various techniques including differential scanning calorimetry, UV spectrometry, electron photoemission and time of flight techniques. The electron photoemission spectra of layers of the amorphous materials showed the ionization potentials of 5.35–5.4 eV. Time-of-flight hole drift mobilities in the amorphous layers of some derivatives exceed 10^?3 cm²/V s at high electric fields.     

Research into nanoparticles obtained by electric explosion of conductive materials

One of the primary nanoparticles production methods is electric explosion of wire (further — EEW) which is known as a physical phenomenon since 1771. Limitation of EEW as a method of nanoparticles production lies in a great dispersion of particle diameters — a spectrum of nano- and micrometric diameters (10³ and higher differences in diameters are likely). Due to great differences in nanoparticles diameters formed by explosion (in aerosol conditioned by explosion), a continuous separation of nanoparticles from aerosol flows is essential. Dispersion of conductor explosion products is mostly affected by a diameter of wire, density of comparative energy, duration of the energy input. Objective of this research is to investigate the vista of producing nanoparticles by EEW at low voltage and high energy surplus using the wire of an enlarged diameter. Analyses have been made by exploding the iron wire of 60 mm length and 0.31 and 0.45 mm diameter and the copper wire of 0.375 and 0.49 mm diameter. Purity of the wire material was 99.5% of iron and 99.9% of copper. To separate nanoparticles from aerosol a separation device was used which consists of a precipitator and three stages centrifugal cyclone. SEM analysis of Fe nanoparticles using SEM showed the mean diameter of particles about 69 nm (for wire Ø0.45 mm). Cu nanoparticles was 97 nm in diameter (for wire Ø0.49 mm). XRD spectra of iron and copper nanoparticles indicated a high oxidation level of Fe and Cu (oxides of different crystollagraphic axes are formed such as Fe₃O₄, Fe₂O₃, CuO, Cu₂O). A moderate quantity of pure Fe and Cu metals (Fe(110), Fe(211), C(l 11), Cu(200)).     

Electrochemical gold deposition from sulfite solution: application for subsequent polyaniline layer formation

Electrochemical gold deposition from sulfite solutions was studied by means of voltammetry, EIS and EQCM. A gold film electrode was used for polyaniline layer formation by electrochemical oxidation of aniline. The standard electrochemical reduction potential of the reaction [Au(SO₃)₂]³⁻ + e⁻ = Au + 2 SO₃²⁻ was determined, and is equal to 0.116 V (vs. NHE). Both solution stirring and temperature increase accelerate the electrochemical reduction of gold, when the electrode potential is below −0.55 V. When the potential is above −0.55 V the electrochemical reduction proceeds via passive layer formation. Our study suggests that the passive layer consists of chemically adsorbed sulfite ions and sulfur. The gold film deposited from sulfite solution is a high quality substrate suitable for conducting polymer layer formation. This technique, where a polymer layer electrode is prepared by thin gold film deposition onto a metal surface and by subsequent polymer layer formation, can be applied in sensor research and technology.     

Ultrahigh Efficiency Fluorescent Single and Bi‐Layer Organic Light Emitting Diodes: The Key Role of Triplet Fusion

A new family of anthracene core, highly fluorescent emitters is synthesized which include diphenylamine hole transport end groups. Using a very simple one or two layer organic light emitting diode (OLED) structure, devices without outcoupling achieve an external quantum efficiency of 6% and photonic efficiencies of 20 cd/A. The theoretical maximum efficiency of such devices should not exceed 3.55%. Detailed photophysical characterization shows that for these anthracene based emitters 2T₁≤T_n and so in this special case, triplet fusion can achieve a singlet production yield of 0.5. Indeed, delayed electroluminescence measurements show that triplet fusion contributes 59% of all singlets produced in these devices. This demonstrates that when triplet fusion becomes very efficient, fluorescent OLEDs even with very simple structures can approach an internal singlet production yield close to the theoretical absolute maximum of 62.5% and rival phosphorescent‐based OLEDs with the added advantage of much improved stability.     

Critical Role of Triplet Exciton Interface Trap States in Bilayer Films of NPB and Ir(piq)3

Investigations are carried out into triplet transfer in bilayer films of NPB (N,N´‐diphenyl‐N,N´‐bis(1‐naphthyl)‐1,1´‐biphenyl‐4,4?‐diamine) and Ir(piq)₃ (Iridium (III) Tris(1‐phenylisoquinoline) using laser light pulses to excite the upper surface of the NPB, and thereafter observing the decay dynamics in the Ir(piq)₃ layer situated beneath the NPB. The NPB layer thickness is varied from 13 nm to 80 nm. The results show that up to 200 ns after excitation, the multiexponential decay of directly excited Ir(piq)₃ is observed, thereafter the decay is monoexponential. It is concluded that this monoexponential decay after 200 ns is due to triplets that are transferred to the Ir(piq)₃ via migration from the NPB. The thicker the NPB layer the longer it takes for the reservoir of NPB triplets to deplete via the Ir(piq)₃, with the result that the apparent monoexponential lifetime of the Ir(piq)₃ increases as the thickness of the NPB films increases. Based on time resolved spectra and decays, it is concluded that triplets arriving from NPB are trapped at interface sites of Ir(piq)₃ and do not migrate directly to the bulk states of Ir(piq)₃. A model based on exciton diffusion kinetics, including the presence of interface trap sites, is described, which accurately predicts this behavior.