Surface defect mitigation via alkyl-ligand-controlled purification for stable and high-luminescence perovskite quantum dots.

Perovskite quantum dots (PQDs) have received considerable attention as fluorescent materials due to their excellent optical properties. However, because PQDs contain ionic bonds, they have the disadvantage of being vulnerable to environmental conditions, so improving their stability is essential. Indeed, recent research has focused on improving both the stability and luminescence of PQDs by mixing them with methyl acetate (MeOAc) to suppress surface defects via purification. MeOAc reacts with the surface ligands of PQDs, resulting in ligand-controlled purification. However, while the ligands are limited for the PQD synthesis, the effect of ligand alkyl-chain length has not been reported. Therefore, we report herein a strategy for obtaining stable PQDs with tunable performances by using amine ligands of various chain lengths. The amine ligand is selected because it is very effective in interacting with the halide vacancies present on the surface of the perovskite crystal structure. The results indicate that MeOAc becomes less effective as the chain length of the ligand is increased, and more effective as the chain length is decreased. Consequently, PQDs treated with MeOAc and a short-chain ligand afford a quantum yield (QY) of 79.2% and are highly stable when exposed to thermal and ambient conditions. Therefore, we suggest a facile approach to suppressing the degradation of PQDs during the fabrication process.

Hand-held all-in-one (HAO) self-test kit for rapid and on-site detection of SARS-CoV-2 with colorimetric LAMP.

Throughout the COVID-19 pandemic, individuals potentially infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were forcibly recalled to local or central hospitals, where the diagnostic results were obtained a couple of days after the liquid biopsies were subjected to conventional polymerase chain reaction (PCR). This slow output of such a complex and time-consuming laboratory procedure hindered its widespread application. To overcome the limitations associated with such a centralized diagnostic system, we developed a hand-held and all-in-one type test kit in which the analytical results can be obtained in only 30 min. The test kit consists of three major steps for on-site SARS-CoV-2 RNA detection: 1) virus lysis by heat, 2) RNA enrichment by membrane, and 3) real-time detection by colorimetric loop-mediated isothermal amplification (c-LAMP). The proposed device operates in a sample-to-answer format, is fully automated, and reduces dependence on traditional laboratory settings, facilitating large-scale population screening.

In Situ Interfacial-Assembly Perovskite Quantum Dot via Marangoni and Capillary Convection Manipulation for Robust Luminescence.

In solid substrates, colloidal solutions produce irregular deposits on the surface by Marangoni flow and capillary flow during evaporation. Reportedly, perovskite quantum dots (PQDs) as a colloidal solution have irregular surfaces based on a similar principle as the coffee ring effect in QD systems when droplets evaporate from the substrate. Given that this issue is due to the direction of Marangoni and capillary flows, the substrate is tilted to change the direction of the flows. The appropriate angle is determined by controlling the angle of the substrate so that the two flows circulate similarly; this method is called "assembly-coating". Herein, we compare the PL intensity before and after the thermal evaporation of the thin films prepared by conventional and assembly-coating. Moreover, by characterizing the diode device (hole-only space charge limited current) for each coating process, the charge carrier characteristics are investigated in detail. Therefore, we suggest a facile strategy to obtain a uniform surface and thermal evaporative stability using colloidal solutions. This strategy is effective in designing surface uniformity and light-emitting layers for colloidal solution deposition and assembly.

One-Pot Synthesis of All-Inorganic CsPbClBr2 Blue Perovskite Quantum Dots via Stoichiometric Precursor.

The synthesis of perovskite-based blue light-emitting particles is valuable for several applications as the excellent optical properties and performances of the constituting materials associated with multi-exciton generation can be exploited. However, the preparation of perovskite precursors requires high temperatures, resulting in a complex manufacturing process. This paper proposes a one-pot method to synthesize CsPbClBr2 blue light-emitting quantum dots (QDs). In the case of nonstoichiometric precursor synthesis, the CsPbClBr2 QDs coexisted with additional products. The solvent for synthesizing mixed perovskite nanoparticles (containing chloride) was selected by mixing dimethylformamide (DMF) and/or dimethyl sulfoxide (DMSO) in different ratios. When only DMF was used with the stoichiometric CsBr and PbX2 (X = Cl, Br) ratio, the quantum yield was 70.55%, and superior optical properties were achieved. Moreover, no discoloration was observed for 400 h, and a high photoluminescence intensity was maintained. When deionized water was added to form a double layer with hexane, the luminescence was maintained for 15 days. In other words, the perovskite did not easily decompose even when in contact with water, which suppressed the release of Pb2+, which are heavy metal atoms in the structure. Overall, the proposed one-pot method for all-inorganic-based perovskite QDs provides a platform for synthesizing superior blue light-emitting materials.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly.

Invited for this month's cover is the group of Jin Kuen Park and Dong Hwan Wang at two different universities in South Korea. The image shows how the supramolecular interaction between pendant polymers can play a role in controlling the electronic properties in perovskite-based electronics such as solar cells and photodetectors. The Full Paper itself is available at 10.1002/cssc.202101785.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly.

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Selective Soxhlets extraction to enhance solubility of newly-synthesized poly(indoloindole-selenophene vinylene selenophene) donor for photovoltaic applications.

An electron-rich fused indoloindole-based poly(indoloindole-selenophene vinylene selenophene) was synthesized and characterized. Soxhlet can be obtained by continuously purifying the product with a specific solvent and obtaining a pure polymer with a high concentration. Molecular weight is affected by the vapor pressure of marginal solvent, and the polymer was fractionated using tetrahydrofuran, chloroform, and chlorobenzene. Solubility is closely related to the morphology of bulk heterojunction and device parameters. In the solution process of fabricating the organic solar cell, securement of solubility has a great effect on the performance of the device, because morphology and orientation of a photo-active layer which significantly affect charge transport in the device. Since tetrahydrofuran (THF) Soxhlet solvents have high vapor pressure and appropriate solubility parameters, THF induced the best solubility of P-IDI-SVS materials for organic solvents. And through additive optimization, the performance of the device based on P-IDI-SVS from THF-Soxhlet extraction was enhanced. This is expected to be a meaningful study because the effect on solubility of Soxhlet solvent suggests factors to be considered in the solution process in organic solar cell research. In addition, surface modified bulk heterojunction was observed using atomic force microscopy, photoluminescence, time-correlated single photon counting and Raman spectroscopy analysis.

Acidity Suppression of Hole Transport Layer via Solution Reaction of Neutral PEDOT:PSS for Stable Perovskite Photovoltaics.

Poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) is typically used for hole transport layers (HTLs), as it exhibits attractive mechanical, electrical properties, and easy processability. However, the intrinsically acidic property can degrade the crystallinity of perovskites, limiting the stability and efficiency of perovskite solar cells (PSCs). In this study, inverted CH3NH3PbI3 photovoltaic cells were fabricated with acidity suppressed HTL. We adjusted PEDOT:PSS via a solution reaction of acidic and neutral PEDOT:PSS. And we compared the various pH-controlled HTLs for PSCs devices. The smoothness of the pH-controlled PEDOT:PSS layer was similar to that of acidic PEDOT:PSS-based devices. These layers induced favorable crystallinity of perovskite compared with acidic PEDOT:PSS layers. Furthermore, the enhanced stability of pH optimized PEDOT:PSS-based devices, including the prevention of degradation by a strong acid, allowed the device to retain its power conversion efficiency (PCE) value by maintaining 80% of PCE for approximately 150 h. As a result, the pH-controlled HTL layer fabricated through the solution reaction maintained the surface morphology of the perovskite layer and contributed to the stable operation of PSCs.

Clinical Performance of the AllplexTM Respiratory Panel 1 Test Compared to SimplexaTM Flu A/B and RSV for Detection of Influenza Virus and Respiratory Syncytial Virus Infection Including Their Subtyping.

OBJECTIVE: TheAllplexTM Respiratory Panel 1 (ARP) is a new assay based on a real-time polymerase chain reaction (RT-PCR) for the detection of influenza A (Flu A), influenza B virus (Flu B), and respiratory syncytial virus (RSV), including subtyping by multiple detection temperature (MuDT) technology. We evaluated the performance of the Allplex Respiratory Panel compared to the SimplexaTM Flu A/B & RSV assay (SP) and other diagnostic tools. MATERIALS AND METHODS: A total of 372 samples were collected from patients at the Korea University Guro Hospital in Seoul, Korea. All samples were tested for influenza virus and RSV by ARP, SP, and an in-house RT-PCR. RESULTS: The sensitivity of ARP was 95.56, 100, and 95.24% for Flu A, Flu B, and RSV, respectively. The specificity of ARP was 100, 100, and 100% for Flu A, Flu B, and RSV, respectively. SP had sensitivities and specificities of 98.89 and 100% for Flu A, 100 and 100% for Flu B, and 100 and 100% for RSV. CONCLUSION: The Allplex panelshowed high sensitivity, specificity, positive predictive, and negative predictive values for the detection of Flu A, Flu B, and RSV. This assay is fast and easy to perform because it takes only about 150 min and there is no need for post-PCR electrophoresis. The ARP can be used as a reliable and convenient assay in clinical laboratories.

Long-Term Stable Transferred Organic Photoactive Layer-Based Photodiode with Controlled Wetting through Interface Stabilization.

The stamping transfer process, which provides a precise patterning of the target material without the limitation of an underlying layer, has attracted significant attention for large-scale roll-to-roll fabrication. Despite the need to minimize the peeling energy, expressed as the sum of adhesion energies, for a simple transfer process, many studies have not considered this effect. In this study, we introduced a wetting coefficient related with adhesions between polymers for the transfer design of organic photosensitive materials. We observed a difference in adhesion between polymer blends depending on the surface energy of the mold. We designed high-surface-energy polyurethane acrylate to enable a residue-free transfer process. The transfer process significantly contributed to the device stability through changes in dark currents, photocurrents, responsivity, and detectivity over time, compared to spin coating. In particular, the detectivity was maintained over 95% after 360 h, and no burn-in loss of internal resistance was observed in the device with a transferred active layer. X-ray photoelectron spectroscopy showed that a large interfacial change between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5- b']dithiophene-2,6-diyl- alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophene-4,6-diyl):[6,6] phenyl C71 butyric acid methyl ester obtained through spin coating occurred owing to solution penetration, whereas the transfer process provided a constant interface owing to morphology stabilization. Therefore, the transfer process with optimized adhesion properties can improve the device operation durability without burn-in loss, enabling a cost-effective fabrication of organic optoelectronic devices.

Covalent organic nanosheets for effective charge transport layers in planar-type perovskite solar cells.

Herein, solvent-treated bandgap-tunable covalent organic nanosheets (CONs) were prepared via the Stille cross-coupling reaction. These materials are considered useful as interlayers in photovoltaic devices upon the alignment of energy levels between other components. Among various types of solar cells, according to the organic-interlayer study, inverted planar perovskite solar cells (PSCs) are mostly demanded to effectively transport and collect charge carriers due to their high performance. At first, the C-V analysis proved the energy levels of the frontier orbitals for CON-10 and CON-16 nanosheets; this verified the suitability of these nanosheets as hole transport layers (HTLs) with the PEDOT:PSS upon casting both films from DMSO. It became evident, however, that the hole transport property of the PEDOT:PSS on the CON-16 layer was unfavorable with the increasing UPS-proven hole injection barrier. In addition, both CONs induced a rough surface morphology; however, CON-10 showed a relatively smooth surface as compared to CON-16 based on the Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) profiles; furthermore, their surface properties influenced both the PEDOT:PSS layers and the perovskite layers. Especially, the XRD profiles presented an enhanced crystallinity of the perovskite layers with CON-10. All these aspects indicate that CON-10 is a more effective HTL material, and several versions of perovskite solar cells (PSCs) have been fabricated with/without CON-10 and CON-16 together with the PEDOT:PSS to determine the more-HTL-suitable CON. As a result, the power conversion efficiencies (PCEs) of the optimized devices with CON-10 exhibited a value of 10.2%, which represented a 1% increase over those of the reference devices without the CONs and was 4% higher than that of the CON-16 devices. Moreover, the devices with CON-10 were further optimized with TiOx using Al electrodes, leading to a PCE increase of these devices that became slightly higher than the PCEs of the device with CON-10 and without TiOx. This tendency was supported by photoluminescence (PL) spectroscopy, photocurrent density (Jph), and space-charge-limited current (SCLC) mobility results.

The Investigation of the Seebeck Effect of the Poly(3,4-Ethylenedioxythiophene)-Tosylate with the Various Concentrations of an Oxidant.

Poly(3,4-ethylenedioxythiophene)-tosylate (PEDOT-Tos) can be synthesized through an in situ polymerization and doping process with iron(III) p-toluenesulfonate hexahydrate as an oxidant. Both the Seebeck coefficient and the electrical conductivity were modified by varying the concentration of the oxidant. We investigated the effects of varying the concentration of the oxidant on the particle sizes and doping (oxidation) levels of PEDOT-Tos for thermoelectric applications. We demonstrated that an increase in the oxidant enabled an expansion of the particle sizes and the doping levels of the PEDOT-Tos. The modification of the doping levels by the concentration of the oxidant can provide another approach for having an optimal power factor for thermoelectric applications. De-doping of PEDOTs by reduction agents has been generally investigated for changing its oxidation levels. In this study, we investigated the effect of the concentration of the oxidant of PEDOT-Tos on the oxidation levels, the electrical conductivities and the Seebeck coefficients. As loading the oxidant of PEDOT-Tos, the Seebeck coefficient was compromised, while the electrical conductivity increased.

Facile NiOx Sol-Gel Synthesis Depending on Chain Length of Various Solvents without Catalyst for Efficient Hole Charge Transfer in Perovskite Solar Cells.

Nickel oxide (NiOx)⁻based perovskite solar cells (PSCs) have recently gained considerable interest, and exhibit above 20% photovoltaic efficiency. However, the reported syntheses of NiOx sol-gel used toxic chemicals for the catalysts during synthesis, which resulted in a high-temperature annealing requirement to remove the organic catalysts (ligands). Herein, we report a facile "NiOx sol-gel depending on the chain length of various solvents" method that eschews toxic catalysts, to confirm the effect of different types of organic solvents on NiOx synthesis. The optimized conditions of the method resulted in better morphology and an increase in the crystallinity of the perovskite layer. Furthermore, the use of the optimized organic solvent improved the absorbance of the photoactive layer in the PSC device. To compare the electrical properties, a PSC was prepared with a p-i-n structure, and the optimized divalent alcohol-based NiOx as the hole transport layer. This improved the charge transport compared with that for the typical 1,2-ethanediol (ethylene glycol) used in earlier studies. Finally, the optimized solvent-based NiOx enhanced device performance by increasing the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), compared with those of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)⁻based devices.

Dry-Stamping-Transferred PC71BM Charge Transport Layer via an Interface-Controlled Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells.

The study of interlayers is important to enhance the performance of inverted perovskite solar cells (PSCs) because interlayers in PSCs align energy levels and improve charge transport. However, previous research into applying interlayers for PSCs has focused only on wet-coated methods, such as spin coating, to form the interlayer. Here, we fabricated planar-type PSCs deposited with a 6,6-phenyl-C71 butyric acid methyl ester (PC71BM) layer onto a CH3NH3PbI3 (MAPbI3) layer by stamping transfer through a relatively dry process condition. We demonstrated the effects of a stamping-transferred PC71BM layer using polyurethane acrylate (PUA), the surface energy of which was modified by 2-hydroxyethyl methacrylate (HEMA) to increase the transfer reproducibility. In PSCs with a stamping-transferred PC71BM layer, we observed an enhanced JSC and a comparable power conversion efficiency (PCE), which were caused by an enhanced coverage of the electron transport layer onto the MAPbI3 layer with preserved crystallinity, which occurs owing to improved electron mobility and exciton dissociation. The optimized device PCE through the dry-transferred PC71BM exhibited a JSC, fill factor, and PCE of 21.65 mA/cm2, 76.0%, and 15.46%, respectively. Moreover, morphological analysis and electrical measurements confirmed the improved durability of dry-stamping-transferred PSCs.

Counterbalancing of morphology and conductivity of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate based flexible devices.

The importance of conductive polymer electrodes with a balance between the morphology and electrical conductivity for flexible organic photovoltaic properties has been demonstrated. Highly transparent PEDOT:PSS anodes with controlled conductivity and surface properties were realized by insertion of dimethyl sulfoxide (DMSO) and a fluorosurfactant (Zonyl) as efficient additives and used for flexible organic photovoltaic cells (OPVs) which are based on a bulk-heterojunction of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):[6,6]phenyl-C71-butyric acid methyl ester (PC71BM). We investigated the correlation between the electrical properties of PEDOT:PSS electrodes and their influences on the surface morphology of the active materials (PTB7:PC71BM). When the device was prepared from the PEDOT:PSS layer functioning as an anode of OPV through an optimized ratio of 5 vol% of DMSO and 0.1 wt% of fluorosurfactant, the devices exhibited improved fill factor (FF) due to the enhanced coverage of PEDOT:PSS films. These results correlate with reduced photoluminescence and increased charge extraction as seen through Raman spectroscopy and electrical analysis, respectively. The conductive polymer electrode with the balance between the morphology and electrical conductivity can be a useful replacement for brittle electrodes such as those made of indium tin oxide (ITO) as they are more resistant to cracking and bending conditions, which will contribute to the long-term operation of flexible devices.