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Mesenchymal stem cell (MSC)-derived small extracellular vesicles (MSC-sEVs) are known to exert immunosuppressive functions. This study showed that MSC-sEVs specifically convert T helper 17 (Th17) cells into IL-17 low-producer (ex-Th17) cells by degrading RAR-related orphan receptor γt (RORγt) at the protein level. In experimental autoimmune encephalomyelitis (EAE)-induced mice, treatment with MSC-sEVs was found to not only ameliorate clinical symptoms but also to reduce the number of Th17 cells in draining lymph nodes and the central nervous system. MSC-sEVs were found to destabilize RORγt by K63 deubiquitination and deacetylation, which was attributed to the EP300-interacting inhibitor of differentiation 3 (Eid3) contained in the MSC-sEVs. Small extracellular vesicles isolated from the Eid3 knockdown MSCs by Eid3-shRNA failed to downregulate RORγt. Moreover, forced expression of Eid3 by gene transfection was found to significantly decrease the protein level of RORγt in Th17 cells. Altogether, this study reveals the novel immunosuppressive mechanisms of MSC-sEVs, which suggests the feasibility of MSC-sEVs as an attractive therapeutic tool for curing Th17-mediated inflammatory diseases.

Al-doped TiO2 (ATO) interfacial layer improves the charge balance and the performance of quantum-dot light-emitting diodes (QLEDs).

Vanadium oxide (V2O5) doped with Li (5, 10, and 15 mol%) was synthesized using an easy and low-cost solution process method and was used as a hole-injection layer (HIL) for quantum-dot light-emitting diodes (QLEDs).

A visible-light phototransistor have been fabricated by adding a solution-processed thin Al2O3 layer under the ZnO layer to improve the visible-light photodetection.

One of the major obstacles in the way of high-performance quantum dot light-emitting diodes (QLEDs) is the charge imbalance arising from more efficient electron injection into the emission layer than the hole injection. In previous studies, a balanced charge injection was often achieved by lowering the electron injection efficiency; however, high performance next-generation QLEDs require the hole injection efficiency to be enhanced to the level of electron injection efficiency. Here, we introduce a solution-processed HfO

We carried out KF postdeposition treatment (PDT) on a Cu(In,Ga)Se2 (CIGS) layer with a process time varying from 50 to 200 s. The highest CIGS solar-cell efficiency was achieved at a KF PDT process time of 50 s; in this condition, we observed the highest level of K element at the near-surface of the CIGS layer and the perfectly passivated pinholes on the CIGS surface. At process times above 150 s, the oversupplied KF agglomerated into large islands and was subsequently eliminated during the deposition of the chemical bath deposition (CBD)-Zn(O,S) buffer layer owing to the islands' water-soluble characteristics. As a result, the growth mechanism of the CBD-Zn(O,S) layer varied as a function of KF PDT process time. X-ray photoemission spectroscopy (XPS) measurements were used to examine the dependency of the chemical state on the KF PDT process time, and from the results, we formulated a chemical reaction model based on the shift in the elemental binding energy following deposition of the CBD-Zn(O,S) buffer layer. The chemical states of the K-In-Se phase, which have a beneficial effect on the solar-cell performance owing to the formation of durable and improved p-n junctions, are formed only at a KF PDT process time of 50 s. We derived band alignments from the XPS depth profiles by extracting the conduction- and valence-band offsets, and we used optical-pump-THz-probe spectroscopy to measure the ultrafast photocarrier lifetimes related to the defect states following KF PDT. Our key findings can be summarized as follows: (i) photocarrier transport is beneficial at a low barrier height, and (ii) the photocarrier lifetime increases when the K-In-Se phases are formed on the CIGS surface, which allows K+ ions to be effectively substituted into Cu vacancies.

A ZnMgO and ZnO double-layered structure was prepared to create a stepwise interfacial electronic structure to improve the electron-injection and electron-transport behaviors in quantum-dot light-emitting diodes (QLEDs). The current density of the electron-only device (EOD) with ZnMgO/ZnO was higher than that of the EOD with only ZnMgO. The detailed QLED interfacial electronic structure was measured using X-ray and ultraviolet photoelectron spectroscopy. A stepwise interfacial electronic structure for electron injection and electron transport was observed connecting the aluminum cathode to the ZnMgO conduction band minimum (CBM) via the ZnO CBM. The QLEDs with the ZnMgO/ZnO double electron transport layer showed an improved performance, with a maximum luminance and current efficiency of 90,892 cd m−2 and 19.2 cd A−1, respectively. Moreover, the turn-on voltage of the device was significantly reduced to 2.6 V due to the stepwise interfacial electronic structure between the aluminum cathode and ZnMgO CBM. This research provides a useful method for developing highly efficient and low turn-on voltage QLEDs using a ZnMgO/ZnO double ETL for next-generation display.

Visible-light phototransistors have been fabricated based on the heterojunction of zinc oxide (ZnO) and titanium oxide (TiO2). A thin layer of TiO2 was deposited onto the spin-coated ZnO film via atomic layer deposition (ALD). The electrical characteristics of the TiO2 layer were optimized by controlling the purge time of titanium isopropoxide (TTIP). The optimized TiO2 layer could absorb the visible-light from the sub-gap states near the conduction band of TiO2, which was confirmed via photoelectron spectroscopy measurements. Therefore, the heterostructure of TiO2/ZnO can absorb and generate photocurrent under visible light illumination. The oxygen-related-states were investigated via X-ray photoelectron spectroscopy (XPS), and the interfacial band structure between TiO2 and ZnO was evaluated via ultraviolet photoelectron spectroscopy (UPS). Oxygen-related states and subgap-states were observed, which could be used to generate photocurrent by absorbing visible light, even with TiO2 and ZnO having a wide bandgap. The optimized TiO2/ZnO visible-light phototransistor showed a photoresponsivity of 99.3 A W−1 and photosensitivity of 1.5 × 105 under the illumination of 520 nm wavelength light. This study provides a useful way to fabricate a visible-light phototransistor based on the heterostructure of wide bandgap oxide semiconductors.

The wide band gap of oxide semiconductors enables them to generate photocurrents through irradiation with high-energy photons, such as by ultraviolet light. To enhance the photoresponsivity of an oxide semiconductor to visible light, we fabricate a phototransistor by doping ZnO with Li. The amount of oxygen vacancies in ZnO is controlled by changing the concentration of lithium hydroxide in ZnO solution. Li dopants increase the electron concentration in ZnO, thereby improving the electrical behavior of ZnO thin-film transistors (TFTs). The Li-doped ZnO TFTs exhibit a high field-effect mobility of 10.15 cm2 V−1 s−1 and a high on/off ratio of ∼107. These oxygen vacancy states are located above the valence band of ZnO; therefore, they can generate a photocurrent upon irradiation of Li-doped ZnO TFTs with visible light. Li-Doped ZnO phototransistors exhibit excellent photodetection characteristics (photoresponsivity: 23.11 A W−1; photosensitivity: 4.94 × 106) upon 520 nm laser irradiation on the device, when the concentration of lithium hydroxide is 5 mol%. In addition, Li doped ZnO TFTs can be operated stably without light-induced aging effects or degradation caused by negative bias stress. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy measurements are performed to investigate the origin of the improved visible-light photoresponsivity of the Li-doped ZnO phototransistors. Our experimental results suggest that a visible-light photodetector can be developed using wide band gap ZnO.

Poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) is a commonly used material for the hole injection layer (HIL) in quantum-dot light-emitting diodes (QLEDs). In this work, we improved the performance of the QLED by using an organic–inorganic hybrid HIL. The hybrid HIL was prepared by mixing PEDOT:PSS with vanadium oxide (V2O5), which is a transition-metal oxide (TMO). The hole injection properties of PEDOT:PSS were improved according to the amount of V2O5 mixed into the PEDOT:PSS. The maximum luminance and current efficiency were 36 198 cd m−2 and 13.9 cd A−1, respectively, when the ratio of PEDOT:PSS and V2O5 was 10 : 1. Moreover, the operating lifetime exceeded 300 h, which is 10 times longer than the lifetime of the device with only PEDOT:PSS HIL. The improvement was analyzed using ultraviolet and X-ray photoelectron spectroscopy. We found that the density of state (DOS) of PEDOT:PSS near the Fermi energy level was increased by mixing V2O5. Therefore, the increase of DOS improved the hole injection and the performance of QLEDs. The result shows that the hybrid HIL can improve the performance and the stability of QLEDs.

We have developed a visible-light phototransistor with excellent photodetection characteristics and stability via atomic layer deposition (ALD) to add a thin layer of aluminum oxide (Al2O3) to quantum dot (QD)/zinc oxide (ZnO) films. Al2O3 was used to passivate the surface of the QDs and fill the interspace of the QDs. This led to a reduction in the number of QD surface traps and prevented damage due to the migration of aggressive metal atoms during electrode deposition. Additionally, some parts of Al2O3 deposited on the surface of ZnO triggered a doping effect by interacting with ZnO. This enhanced the electrical properties of ZnO TFTs by providing an extra electron and allowed the efficient transfer of photoelectrons from the QDs to ZnO by reducing the conduction band minimum of ZnO. Therefore, upon 520 nm laser irradiation Al2O3/QD/ZnO TFTs exhibited excellent photodetection characteristics (e.g., photosensitivity: 3.8 × 107, photoresponsivity: 46.8 A W−1, and photodetectivity: 4.5 × 1014 Jones) at a gate voltage of −5 V. Excellent electrical properties, such as saturation mobility of 1.72 cm V−1 s−1 and on/off current ratio of 1.8 × 106, were also realized. Furthermore, the photo-excited charge transfer mechanism was investigated using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and time-resolved photoluminescence. Our experimental results suggest a method for realizing enhanced optoelectronic characteristics and stability of QD/ZnO TFTs via ALD-Al2O3 deposition, which is useful for developing high-performance visible phototransistors.

Mouse mesenchymal stem cells (MSCs) have been shown to suppress T cells. Especially, MSC-cultured media have shown suppressive functions against various immune cells including the T cells. However, the underlying immunosuppressive mechanisms of the MSC-cultured medium are not yet fully understood. In this study, we confirmed the T cell-suppression capacity of MSC culture supernatant (MSC-CS) through both apoptosis and cell cycle arrest, and hypothesized that the exosomes were the major immunosuppressive agents in the MSC-CS. MSC-derived exosomes (MSC-exo) exhibited potent suppressive effects on T cell proliferation while the rest of the supernatant fraction did not. Interestingly, the exosomes derived from MSC only induced the cell cycle arrest, and it was through the upregulation of p27kip1 protein and downregulation of Cdk2 protein. In conclusion, the exosomes secreted from MSCs could suppress the activated T cell proliferation through the induction of cell cycle arrest.

Zinc oxide (ZnO) is a commonly used electron transport layer in quantum-dot light-emitting diodes (QLEDs). In this study, we used a highly conductive ZnO film via a low-temperature process to improve the electron transport behavior of the QLEDs. The electron transport behavior of ZnO film was investigated from the electron only device, and the origin of high conductivity was figured out using x-ray photoelectron spectroscopy. We found that the oxygen vacancy, which can improve the carrier transport in ZnO film, was increased according to reduce the process temperature of ZnO. Meanwhile, the hydroxyl group, which contribute to the quenching effect, was decreased according to reduce the process temperature of ZnO. Therefore, high-performance QLEDs were fabricated using the low-temperature processed ZnO, and it showed an improved luminance and current efficiency in a full current range. The maximum luminance and current efficiency of the devices were measured as 65,391 Cd/m2 and 2.48 Cd/A, respectively. Moreover, the lifetime of the device was improved due to the low-temperature process. Therefore, we suggest that a highly conductive ZnO film could be formed through a low-temperature process, and it can improve the performance of QLEDs.

Conventional visible-light phototransistors based on the heterostructure of wide band gap zinc oxide (ZnO) and colloidal quantum dots (CdSe/ZnS QDs) have been studied. However, it is found that there are various deteriorated characteristics for their photoelectric behavior. Here, the phototransistors of an additional thin layer of TiO2 deposited onto the ZnO/QDs film using atomic layer deposition are developed for improving the performance of phototransistors. Small band gap QDs can absorb low-energy visible light and generate photoexcited charge carriers, which can be injected into the conduction band of wide band gap ZnO. Subsequently, the photoexcited charge carriers can be injected into the conduction band of TiO2 owing to the low injection barrier. Therefore, the ZnO/QDs phototransistor with the TiO2 layer can generate a larger photocurrent from visible light compared to a device without the TiO2 top layer. Moreover, the inorganic TiO2 layer improved the stability of the device. Under illumination with light at a wavelength of 520 nm, the maximum photosensitivity of the device was 4.2 × 106 and the transition rate was 0.728 ns−1, which is high enough to reduce the persistent photocurrent effect. This work offers a useful method to enhance the performance of visible-light phototransistors based on a heterostructure of oxide semiconductors and QDs.

High-luminance, efficient quantum-dot light-emitting diodes (QLEDs) have been achieved by optimizing the balance between the hole injection layer (HIL) and the hole transport layer (HTL). Different concentrations of vanadium oxide (V2O5) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(4-sec-butylphenyl)diphenylamine)] (TFB) solutions were used to form the efficient HIL and HTL, respectively, for the QLEDs. The hole injection and transport behavior was characterized by using hole-only devices (HODs). The QLEDs, which were prepared with 0.5 wt.% of V2O5 and 0.1 wt.% of TFB as HIL and HTL, respectively, showed a maximum current efficiency of 2.27 cd·A−1 and a maximum luminance of 71,260 cd·m−2. Moreover, the turn-on voltage of the device was as low as 2.2 V due to the efficient carrier injection and transport. The results provide useful information for fabricating high-performance QLEDs.

The C-terminal fragment of CABIN1 interacts with calcineurin and represses the transcriptional activity of the nuclear factor of activated T cells (NFAT). However, the specific sequences and mechanisms through which it binds to calcineurin are unclear. This study determined that decameric peptide (CABIN1 residues 2146–2155) is minimally required for binding to calcineurin. This peptide contains a unique “PPTP” C-terminal sequence and a “PxIxIT” N-terminal motif. Furthermore, p38MAPK phosphorylated the threonine residue of the “PPTP” sequence under physiological conditions, dramatically enhancing the peptide’s binding affinity to calcineurin. Therefore, the CABIN1 peptide inhibited the calcineurin-NFAT pathway and the activation of T cells more efficiently than the VIVIT peptide without affecting calcineurin’s phosphatase activity. The CABIN1 peptide could thus be a more potent calcineurin inhibitor and provide therapeutic opportunities for various diseases caused by the calcineurin-NFAT pathway.

We carried out KF postdeposition treatment (PDT) on a Cu(In,Ga)Se

Islet transplantation is efficacious to prevent severe hypoglycemia and glycemic liability of selected patients of type 1 diabetes. However, since calcineurin inhibitor (CNI) causes β-cell and nephrotoxicity, alternative drug(s) with similar potency and safety profile to CNI will be highly desirable. Here we tested whether JAK3 inhibitor, tofacitinib could be used instead of tacrolimus in CIT07 immunosuppression regimen in cynomolgus nonhuman primate (NHP) model. Five independent streptozotocin (STZ)-induced diabetic monkeys were transplanted with MHC-mismatched allogeneic islets and three animals were further re-transplanted upon insufficient glycemic control or early islet graft rejection. After islet transplantation, blood glucose levels were quickly stabilized and maximal islet graft survival as measured by serum C-peptide concentration was >330, 98, >134, 31, or 22 days, respectively, after transplantation (median survival day; 98 days). Cellular and humoral immune responses were efficiently suppressed by JAK3 inhibitor-based immunosuppression during the follow-up periods. Although intermittent increases of the genome copy number of cynomolgus cytomegalovirus (CMV) were detected by quantitative real-time PCR analyses, serious infections or posttransplant lymphoproliferative disease (PTLD) was not found in all animals. Taken together, we have shown that JAK3 inhibitor could be used in replacement of tacrolimus in a highly translatable NHP islet transplantation model and these results suggest that JAK3 inhibitor will be potentially incorporated in human allogeneic islet transplantation.

Red, green, blue (RGB) selective zinc oxide (ZnO) phototransistors with multi-photoactive quantum-dot (QD) channels have been fabricated by a charge-assisted layer-by-layer (LbL) patterning process. QDs were patterned as RGB pixels in multi-photoactive QD channels through the LbL process. The solution-processed ZnO film, which acts as an active-channel layer of the ZnO TFTs, is patterned via a photoinduced surface engineering method to reduce the leakage current of the ZnO TFTs. The average off-current of the patterned ZnO TFTs reduced from 10−10 to 10−11 A. QDs absorb visible light and generate photoelectrons, which are then transferred to the ZnO to produce photocurrents. The device shows photoresponsivity of 9.4 mA/W, 12.5, and 137 A/W to the illumination of 638, 520, and 405 nm wavelength light. Our results suggest a promising way to develop an RGB selective phototransistor that uses QDs as a visible light absorption layer and ZnO as an active channel semiconductor.

A low-temperature solution-processable inorganic vanadium oxide (V2O5) hole injection layer (HIL) was synthesized for flexible quantum-dot light-emitting diodes (QLEDs). Efficient hole injection characteristics were observed in the hole-only devices; furthermore, the process temperature of V2O5 was as low as 30 °C. We investigated the source of the efficient hole injection behavior using ultraviolet and x-ray photoelectron spectroscopy. The density of gap states was found to increase in accordance with process temperature reduction. Therefore, QLEDs with low-temperature solution-processable V2O5 HILs were fabricated on a glass substrate, which showed excellent characteristics. The maximum luminance and luminous efficiency of the device were 56,717 Cd/m2 and 4.03 Cd/A, respectively. Due to the low-temperature process of the V2O5 HIL, it was also possible to fabricate QLEDs on a flexible plastic substrate without mechanical or thermal deformation of the substrate. Our results suggest that the low-temperature V2O5 inorganic HIL is a feasible alternative to organic HILs for flexible QLEDs.

The interfacial electronic structure between a W-doped In2O3 (IWO) transparent electrode and a V2O5 hole injection layer (HIL) has been investigated using ultraviolet photoelectron spectroscopy for high-performance and inorganic quantum-dot light-emitting diodes (QLEDs). Based on the interfacial electronic structure measurements, we found gap states in a V2O5 HIL at 1.0 eV below the Fermi level. Holes can be efficiently injected from the IWO electrode into poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(4-sec-butylphenyl)diphenylamine)] (TFB) through the gap states of V2O5, which was confirmed by the hole injection characteristics of a hole-only device. Therefore, conventional normal-structured QLEDs were fabricated on a glass substrate with the IWO transparent electrode and V2O5 HIL. The maximum luminance of the device was measured as 9443.5 cd m−2. Our result suggests that the IWO electrode and V2O5 HIL are a good combination for developing high-performance and inorganic QLEDs.

The photocurrent characteristics of zinc-oxide (ZnO) thin-film transistors (TFTs) prepared using radio-frequency sputtering and spin-coating methods were investigated. Various characterization methods were used to compare the physical and the chemical properties of the sputtered and the spin-coated ZnO films. X-ray photoelectron spectroscopy was used to investigate the chemical composition and state of the ZnO films. The transmittance and the optical band gap were measured by using UV-vis spectrometry. The crystal structures of the prepared ZnO films were examined by using an X-ray diffractometer, and the surfaces of the films were investigated by using scanning electron microscopy. ZnO TFTs were prepared using both sputter and solution processes, both of which showed photocurrent characteristics when illuminated by light. The sputtered ZnO TFTs had a photoresponsivity of 3.08 mA/W under illumination with 405-nm light while the solution-processed ZnO TFTs had a photoresponsivity of 5.56 mA/W. This study provides useful information for the development of optoelectronics based on ZnO.

Visible-light phototransistors have been fabricated based on the heterojunction of zinc oxide (ZnO) and titanium oxide (TiO

Dual-functional quantum-dots light emitting diodes (QLEDs) have been fabricated using solution processable vanadium oxide (V2O5) hole injection layer to control the carrier transport behavior. The device shows selectable functionalities of photo-detecting and light-emitting behaviors according to the different operating voltage conditions. The device emitted a bright green light at the wavelength of 536 nm, and with the maximum luminance of 31,668 cd/m2 in a forward bias of 8.6 V. Meanwhile, the device could operate as a photodetector in a reverse bias condition. The device was perfectly turned off in a reverse bias, while an increase of photocurrent was observed during the illumination of 520 nm wavelength light on the device. The interfacial electronic structure of the device prepared with different concentration V2O5 solution was measured in detail using x-ray and ultraviolet photoelectron spectroscopy. Both the highest occupied molecular orbital and the gap state levels were moved closer to the Fermi level, according to increase the concentration of V2O5 solution. The change of gap state position enables to fabricate a dual-functional QLEDs. Therefore, the device could operate both as a photodetector and as a light-emitting diode with different applied bias. The result suggests that QLEDs can be used as a photosensor and as a light-emitting diode for the future display industry.