Graphene-Based Intrinsically Stretchable 2D-Contact Electrodes for Highly Efficient Organic Light-Emitting Diodes.

Intrinsically stretchable organic light-emitting diodes (ISOLEDs) are becoming essential components of wearable electronics. However, the efficiencies of ISOLEDs have been highly inferior compared with their rigid counterparts, which is due to the lack of ideal stretchable electrode materials that can overcome the poor charge injection at 1D metallic nanowire/organic interfaces. Herein, highly efficient ISOLEDs that use graphene-based 2D-contact stretchable electrodes (TCSEs) that incorporate a graphene layer on top of embedded metallic nanowires are demonstrated. The graphene layer modifies the work function, promotes charge spreading, and impedes inward diffusion of oxygen and moisture. The work function (WF) of 3.57 eV is achieved by forming a strong interfacial dipole after deposition of a newly designed conjugated polyelectrolyte with crown ether and anionic sulfonate groups on TCSE; this is the lowest value ever reported among ISOLEDs, which overcomes the existing problem of very poor electron injection in ISOLEDs. Subsequent pressure-controlled lamination yields a highly efficient fluorescent ISOLED with an unprecedently high current efficiency of 20.3 cd A-1 , which even exceeds that of an otherwise-identical rigid counterpart. Lastly, a 3 inch five-by-five passive matrix ISOLED is demonstrated using convex stretching. This work can provide a rational protocol for designing intrinsically stretchable high-efficiency optoelectronic devices with favorable interfacial electronic structures.

Efficient Photon Extraction in Top-Emission Organic Light-Emitting Devices Based on Ampicillin Microstructures.

The desire to enhance the efficiency of organic light-emitting devices (OLEDs) has driven to the investigation of advanced materials with fascinating properties. In this work, the efficiency of top-emission OLEDs (TEOLEDs) is enhanced by introducing ampicillin microstructures (Amp-MSs) with dual phases (α-/ß-phase) that induce photoluminescence (PL) and electroluminescence (EL). Moreover, Amp-MSs can adjust the charge balance by Fermi level (EF ) alignment, thereby decreasing the leakage current. The decrease in the wave-guided modes can enhance the light outcoupling through optical scattering. The resulting TEOLED demonstrates a record-high external quantum efficiency (EQE) (maximum: 68.7% and average: 63.4% at spectroradiometer; maximum: 44.8% and average: 42.6% at integrating sphere) with a wider color gamut (118%) owing to the redshift of the spectrum by J-aggregation. Deconvolution of the EL intensities is performed to clarify the contribution of Amp-MSs to the device EQE enhancement (optical scattering by Amp-MSs: 17.0%, PL by radiative energy transfer: 9.1%, and EL by J-aggregated excitons: 4.6%). The proposed TEOLED outperforms the existing frameworks in terms of device efficiency.

Improved device efficiency and lifetime of perovskite light-emitting diodes by size-controlled polyvinylpyrrolidone-capped gold nanoparticles with dipole formation.

Herein, an unprecedented report is presented on the incorporation of size-dependent gold nanoparticles (AuNPs) with polyvinylpyrrolidone (PVP) capping into a conventional hole transport layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The hole transport layer blocks ion-diffusion/migration in methylammonium-lead-bromide (MAPbBr3)-based perovskite light-emitting diodes (PeLEDs) as a modified interlayer. The PVP-capped 90 nm AuNP device exhibited a seven-fold increase in efficiency (1.5%) as compared to the device without AuNPs (0.22%), where the device lifetime was also improved by 17-fold. This advancement is ascribed to the far-field scattering of AuNPs, modified work function and carrier trapping/detrapping. The improvement in device lifetime is attributed to PVP-capping of AuNPs which prevents indium diffusion into the perovskite layer and surface ion migration into PEDOT:PSS through the formation of induced electric dipole. The results also indicate that using large AuNPs (> 90 nm) reduces exciton recombination because of the trapping of excess charge carriers due to the large surface area.

Peripheral Nerve Block for Hip Arthroscopy Does Not Have any Clinical Advantage Compared With Local Anesthetic Regarding Pain Management: A Meta-analysis of Randomized Controlled Trials.

PURPOSE: To evaluate the efficacy of peripheral nerve block on reduction in opioid consumption and pain control after hip arthroscopy. METHOD: To identify studies evaluating the effects of peripheral nerve block on pain control and reduction in opioid consumption in hip arthroscopy, we searched all records in the PubMed, Embase, and Cochrane Library databases until May 2021. Studies with the following characteristics were considered eligible: 1) patients who underwent a hip arthroscopy (population); 2) patients who received peripheral nerve block (intervention); 3) patients who did not receive peripheral nerve block (comparator); 4) record of total opioid consumption as a primary outcome and pain level at 1, 3 to 6, and 24 hours after surgery, patient satisfaction, and incidence of nausea and vomiting as secondary outcomes (outcomes); and 5) randomized controlled trial (study design). Data were independently extracted by two reviewers and synthesized using a random or fixed-effects model, according to the heterogeneity. RESULTS: Eight RCTs were finally included in the meta-analysis. There were no significant differences in postoperative opioid consumption at 24 hours (standardized mean difference [SMD] = -0.091, 95% confidence interval [CI] [-0.270, 0.089]) or in visual analog scale (VAS) score at 1 (SMD = 0.299, 95% CI [-0.758, 0.160]), 3 to 6 (SMD = -0.304, 95% CI [-0.655, 0.047]), and 24 (SMD = -0.230, 95% CI [-0.520, 0.060]) hours postoperatively between the peripheral nerve block and control groups. Moreover, no significant differences were observed in patient satisfaction (SMD < 0.001, 95% CI [-0.284, 0.284]) or the incidence of nausea and vomiting (SMD = 0.808, 95% CI [0.311, 2.104]) between the two groups. CONCLUSION: Peripheral nerve block for hip arthroscopy has no clinical advantage regarding pain management after surgery when compared with the group that received the local infiltration of analgesics without peripheral nerve block. LEVEL OF EVIDENCE: Level II, meta-analysis of level I and II randomized controlled trials (RCTs).

Highly efficient, heat dissipating, stretchable organic light-emitting diodes based on a MoO3/Au/MoO3 electrode with encapsulation.

Stretchable organic light-emitting diodes are ubiquitous in the rapidly developing wearable display technology. However, low efficiency and poor mechanical stability inhibit their commercial applications owing to the restrictions generated by strain. Here, we demonstrate the exceptional performance of a transparent (molybdenum-trioxide/gold/molybdenum-trioxide) electrode for buckled, twistable, and geometrically stretchable organic light-emitting diodes under 2-dimensional random area strain with invariant color coordinates. The devices are fabricated on a thin optical-adhesive/elastomer with a small mechanical bending strain and water-proofed by optical-adhesive encapsulation in a sandwiched structure. The heat dissipation mechanism of the thin optical-adhesive substrate, thin elastomer-based devices or silicon dioxide nanoparticles reduces triplet-triplet annihilation, providing consistent performance at high exciton density, compared with thick elastomer and a glass substrate. The performance is enhanced by the nanoparticles in the optical-adhesive for light out-coupling and improved heat dissipation. A high current efficiency of ~82.4 cd/A and an external quantum efficiency of ~22.3% are achieved with minimum efficiency roll-off.

Impact of tunable 2-(1H-indol-3-yl)acetonitrile based fluorophores towards optical, thermal and electroluminescence properties.

Herein, we have synthesized 4,5-diphenyl-1H-imidazole and 2-(1H-indol-3-yl)acetonitrile based donor-π-acceptor fluorophores and studied their optical, thermal, electroluminescence properties. Both the fluorophores exhibit high fluorescence quantum yield (Φ f = <0.6) and good thermal stability (T d10 = <300 °C), and could be excellent candidates for OLED applications. Moreover, the ground and excited state properties of the compounds were analysed in various solvents with different polarities. The geometric and electronic structures of the fluorophores in the ground and excited states have been studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The absorption of BIPIAN and BITIAN in various solvents corresponds to S0 → S1 transitions and the most intense bands with respect to the higher oscillator strengths are mainly contributed by HOMO → LUMO transition. Significantly, the vacuum deposited non-doped OLED device was fabricated using BITIAN as an emitter, and the device shows electroluminescence (EL) at 564 nm, maximum current efficiency (CE) 0.687 cd A-1 and a maximum external quantum efficiency (EQE) of 0.24%.

Replacement of n-type layers with a non-toxic APTES interfacial layer to improve the performance of amorphous Si thin-film solar cells.

Hydrogenated amorphous Si (a-Si:H) thin-film solar cells (TFSCs) generally contain p/n-type Si layers, which are fabricated using toxic gases. The substitution of these p/n-type layers with non-toxic materials while improving the device performance is a major challenge in the field of TFSCs. Herein, we report the fabrication of a-Si:H TFSCs with the n-type Si layer replaced with a self-assembled monolayer (3-aminopropyl) triethoxysilane (APTES). The X-ray photoelectron spectroscopy results showed that the amine groups from APTES attached with the hydroxyl groups (-OH) on the intrinsic Si (i-Si) surface to form a positive interfacial dipole towards i-Si. This interfacial dipole facilitated the decrease in electron extraction barrier by lowering the work function of the cathode. Consequently, the TFSC with APTES showed a higher fill factor (0.61) and power conversion efficiency (7.68%) than the reference device (without APTES). This performance enhancement of the TFSC with APTES can be attributed to its superior built-in potential and the reduction in the Schottky barrier of the cathode. In addition, the TFSCs with APTES showed lower leakage currents under dark conditions, and hence better charge separation and stability than the reference device. This indicates that APTES is a potential alternative to n-type Si layers, and hence can be used for the fabrication of non-toxic air-stable a-Si:H TFSCs with enhanced performance.

Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer.

We studied the effect of direct charge trapping at different doping concentrations on the device performance in tris(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T) as a host-dopant system of a fluorescent organic light-emitting diode. With increasing C545T doping concentration, trap sites could lead to the promotion of hole injection and the suppression of electron injection due to the electron-transport character of Alq3 host for each carriers, as confirmed by hole- and electron-only devices. Direct charge injection of hole carriers from the hole transport layer into C545T dopants and the charge trapping of electron carriers are the dominant processes to improve the charge balance and the corresponding efficiency. The shift of the electroluminescence (EL) spectra from 519 nm to 530 nm was confirmed the exciton formation route from Förster energy transfer of host-dopant system to direct charge trapping of dopant-only emitting systems. Variation in the doping concentration dictates the role of the dopant in the fluorescent host-dopant system. Even though concentration quenching in fluorescent dopants is unavoidable, relatively heavy doping is necessary to improve the charge balance and efficiency and to investigate the relationship between direct charge trapping and device performance. Heavy doping at a doping ratio of 6% also generates heavy exciton quenching and excimer exciton, because of the excitons being close enough and dipole-dipole interactions. The optimum device performance was achieved with a 4%-doped device, retaining the high efficiency of 12.5 cd/A from 100 cd/m(2) up to 15,000 cd/m(2).

Effects of Gold-Nanoparticle Surface and Vertical Coverage by Conducting Polymer between Indium Tin Oxide and the Hole Transport Layer on Organic Light-Emitting Diodes.

The effect of varying degrees of surface and vertical coverage of gold nanoparticles (Au-NPs) by poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) ( PEDOT: PSS), which was used as a capping layer between indium tin oxide (ITO) and a hole transport layer (HTL) on small-molecule fluorescent organic light-emitting diodes (OLEDs), was systemically investigated. With respect to the Au-NP loading amount and size, the resultant current densities influenced the charge balance and, therefore, the OLED device performance. When the capping layer consisted of ITO/Au-NPs/ PEDOT: PSS+Au-NPs, superior device performance was obtained with 10-nm Au-NPs through increased surface coverage in comparison to other Au-NP PEDOT:PSS coverage conditions. Furthermore, the Au-NP size determined the vertical coverage of the capping layer. The current densities of OLEDs containing small Au-NPs (less than 30 nm, small vertical coverage) covered by PEDOT: PSS decreased because of the suppression of the hole carriers by the Au-NP trapping sites. However, the current densities of the devices with large Au-NPs (over 30 nm, large vertical coverage) increased. The increased electromagnetic fields observed around relatively large Au-NPs under electrical bias were attributed to increased current densities in the OLEDs, as confirmed by the finite-difference time-domain simulation. These results show that the coverage conditions of the Au-NPs by the PEDOT: PSS clearly influenced the OLED current density and efficiency.

Highly efficient hybrid thin-film solar cells using a solution-processed hole-blocking layer.

We report the origin of the improvement of the power conversion efficiency (PCE) of hybrid thin-film solar cells when a soluble C(60) derivative, [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM), is introduced as a hole-blocking layer. The PCBM layer could establish better interfacial contact by decreasing the reverse dark-saturation current density, resulting in a decrease in the probability of carrier recombination. The PCE of this optimized device reached a maximum value of 8.34% and is the highest yet reported for hybrid thin-film solar cells.

Direct growth of SnO2 nanowires on WOx thin films.

Single-crystalline SnO(2) nanowires were directly grown on an amorphous WO(x) thin film, leading to the formation of nano-scale contacts with a near-Ohmic conductance. The WO(x) facilitated the diffusion of SnO(2) on the surface of the WO(x) thin film, and SnO(2) nanowires could be uniformly grown from the diffused SnO(2). The contact properties between the metallic WO(x) and a semiconducting SnO(2) nanowire were examined. The resistivity of the WO(x)-SnO(2) nanowire contact was found to be approximately 2.6 × 10(-5) Ω cm(2). This was comparable to the resistivity of a contact between an Al electrode and a SnO(2) nanowire with a contact area. A fabricated SnO(2) nanowire transistor exhibited an on-current of approximately 386 nA, a threshold voltage of approximately 3.8 V, a subthreshold slope of approximately 0.26 V/dec and a field-effect mobility of approximately 43 cm(2) V(-1) s(-1).

High efficiency inorganic/organic hybrid tandem solar cells.

Hybrid tandem solar cells comprising an inorganic bottom cell and an organic top cell have been designed and fabricated. The interlayer combination and thickness matching were optimized in order to increase the overall photovoltaic conversion efficiency. A maximum power conversion efficiency of 5.72% was achieved along with a V(oc) of 1.42 V, reaching as high as 92% of the sum of the subcell V(oc) values.

Lateral buckling mechanics in silicon nanowires on elastomeric substrates.

We describe experimental and theoretical studies of the buckling mechanics in silicon nanowires (SiNWs) on elastomeric substrates. The system involves randomly oriented SiNWs grown using established procedures on silicon wafers, and then transferred and organized into aligned arrays on prestrained slabs of poly(dimethylsiloxane) (PDMS). Releasing the prestrain leads to nonlinear mechanical buckling processes that transform the initially linear SiNWs into sinusoidal (i.e., "wavy") shapes. The displacements associated with these waves lie in the plane of the substrate, unlike previously observed behavior in analogous systems of silicon nanoribbons and carbon nanotubes where motion occurs out-of-plane. Theoretical analysis indicates that the energy associated with this in-plane buckling is slightly lower than the out-of-plane case for the geometries and mechanical properties that characterize the SiNWs. An accurate measurement of the Young's modulus of individual SiNWs, between approximately 170 and approximately 110 GPa for the range of wires examined here, emerges from comparison of theoretical analysis to experimental observations. A simple strain gauge built using SiNWs in these wavy geometries demonstrates one area of potential application.

Highly efficient organic light-emitting diodes with a quantum dot interfacial layer.

Advanced organic light-emitting diodes (OLEDs), based on a multiple structure, were achieved in combination with a quantum dot (QD) interfacial layer. The authors used core/shell CdSe/ZnS QDs passivated with trioctylphosphine oxide (TOPO) and TOPO-free QDs as interlayers. Multiple-structure OLEDs (MOLEDs) with TOPO-free QDs showed higher device efficiency because of a well-defined interfacial monolayer formation. Additionally, the three-unit MOLED showed high performance for device efficiency with double-structured QD interfacial layers due to the enhanced charge balance and recombination probability.