We developed the stable, ultra-fast vertical polyimide capacitive-type humidity sensor with a response time of 10 ms order using fluorinated polyimide with a multi-walled carbon nanotube (CNT) gas permeable upper electrode. On the basis of the diffusion model, the response time is reduced to less than 0.1s by reducing the hydrophobic partially fluorinated polyimide dielectric layer to ca. 100 nm. Although the sensitivity increases with the reduction of polyimide (inversely proportional) thickness, the recovery time increases and non-linear sensitivity are observed after the exposure to a high-humid air (> 80 %RH). The slow recovery and instability were improved by the insertion of ultra-thin perfluoro polymer (Cytop).

Droplet-based electricity generators (DEG) have been demonstrated as a feasible and promising method of energy harvesting from environmental water, such as rain and tap water. However, the high material costs, the large usage of fluoropolymer and the low output power density are still challenges for DEGs to be used as practical applications. In this study, we proposed a DEG of a three-layer structure composed of polyimide layer, tungsten trioxide (WO3), and an ultra-thin fluoropolymer layer. Then the effects of the multilayer structure of the DEG and the droplet parameters (type of droplet, volume, and falling height) on its performance was investigated through the measurements of surface potential and voltage waveform. By optimizing the parameters for micro-meter order thick polyimide, the performance of the DEG was significantly improved, and the voltage of 10 V orders and a peak power of 2.7 mW was achieved by a 50 mu l single water droplet, which was sufficient to light a small LED.

We fabricated the solution-processed multilayered light-emitting diodes having the colloidal quantum dots/ polymer blend as an emitting layer (QD-LEDs) with the inverted organic LED structure. We proposed the multilayered electron injection layers consisting of 4,7-Dimethoxy-1,10-phenanthroline (p-MeO-Phen) on ZnO nanoparticles, and the multilayers of ZnO:p-MeO-Phen blend (1st EIL) and the heat-treated Zr (IV) acetylacetonate (Zr(acac)4) as a 2nd EIL. We achieved a higher material utilization rate and multilayered structure by combining the meniscus coating and transfer printing techniques. We then fabricated the QD-LEDs consisting of ITO/ZnO or ZnO:p-MeO-Phen blend (1st EIL)/2nd EIL/QD: polymer blend/polyvinylcarbazole (PVCz)/Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB)/hole injection layer/Anode (Al or Ag). We compared the device performance of QD blended with PVCz and polymethylmethacrylate (PMMA). The thickness of the QD layer was controlled between 1 and 3 QD layers by repeating the meniscus coating and transfer printing. The work function of ZnO was reduced by p-MeO-Phen and the threshold voltage was reduced from 4.9 V to 2.95 V. The peak value of EQE was improved from 1.14% to 3.1% by insertion of Zr(acac)4 probably owing to the reduction of leakage current and exciton quenching.

We have improved the operation voltage and external quantum efficiencies of blue-light emitting polymer-based inverted organic light emitting diodes (iPLED) by inserting solution processable Al acetylacetonate (Al (acac)3) thin film and electron transporting layer (ETL) between the ZnO nanoparticles and poly(9,9-dioctylfluorene) (F8) emission layers. Using meniscus-coating on silicon elastomer and transfer-printing methods, the deposition time and the material loss of electron-injection layers, polymeric light-emitting layer and polymeric hole-transporting layers were decreased to less than 1/10 compared with the conventional spin-coating. The insertion of these layers improves exciton quenching and carrier balance, and we obtained the external quantum efficiency of 2.2% and low threshold voltage of 2.7 V for the blue-light emitting multilayered polymer LEDs with Al(acac)3 and solution processed ETL.

We demonstrated the low-cost, eco-friendly fabrication techniques for inverted perovskite solar cells (iPSCs) with multilayered electron transporting layers using fullerene derivative (PCBM) and ZnO nanoparticles (NPs) by combining the meniscus-coating, push-coating, and transfer-printing techniques. We fabricated the multilayered planar iPSCs by low-temperature printing process not higher than 120(degrees)C. Using meniscus coating method by reciprocating the glass rod back and forth repeatedly for 2-10 times, the material usage of PCBM and toxic chlorobenzene for iPSCs to 1/15 similar to 1/20 compared with the conventional spin-coating method, and 1/10 for ZnO NPs without extending the tact time. The material utilization rate became about 50% and 100% for meniscus- and push-coating, and a pin-hole-free uniform film was obtained for meniscus coating. We also reduced the initial degradation of perovskite layer during the deposition of ZnO onto the perovskite layer and improved the photovoltaic properties by the transfer-printing of ZnO from "wet-PDMS" stamp onto the thin PCBM film coated perovskite layers.

We have developed polymer-based inverted organic light emitting diodes (iOLED) with multilayered structure using orthogonal solvent, meniscus-coating and transfer-printing and push-coating techniques for the low-cost, eco-friendly fabrication for iOLEDs. Using meniscus coating method by reciprocating the glass rod back and forth repeatedly for 2-10 times, the material usage of electron-injection layers, polymeric light-emitting layer and polymeric hole-transporting layers were decreased to 1/10 for the film deposited onto glass slide and to ca. 1/20 for the film deposited onto the elastomer stamp compared with the conventional spin-coating method. We obtained higher external quantum efficiency and lower operation voltage with solution processable hole-injection layer, and silver anode. The improvements in threshold voltage and the maximum EQE were observed for the device with electron-transporting EIL, such as alcohol soluble phenanthroline derivative, which is an effective way to reduce the number of multilayers and the tact time for fabricating iOLEDs.

We have developed polymer-based inverted organic LEDs (iOLED) with a multilayered structure using orthogonal solvent, transfer-printing, improved meniscus-coating method that moves back and forth. Reciprocating the glass rod back and forth repeatedly, the material usage of electron-injection layers, polymeric light-emitting layer and polymeric hole-transporting layers were decreased to 1/10 for the film deposited onto the glass slide and to ca. 1/20 for the film deposited onto the elastomer stamp compared with the conventional spin-coating. We obtained higher external quantum efficiency (EQE) and lower operation voltage with solution processable metal oxide hole-injection layer and silver anode. The improvements in the threshold voltage and the maximum EQE were observed for the device with electron-transporting EIL, such as alcohol soluble phenanthroline derivative, which is an effective way to reduce the number of multilayers and the tact time for fabricating iOLEDs.

We report on the FET properties of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) on a HfO2/alicyclic polyimide double-layered gate insulator at an elevated temperature. The patterning of semiconductor and polymeric insulator layers is also discussed using the surface selective deposition of solution onto the wettable region (self-assembled monolayer-coated oxide layer) and unwettable region (bare metal oxide layer) obtained by vacuum ultraviolet light (172 nm) irradiation. A multilayered film of 20-30 nm thick Ph-BTBT-10 and a double-layered gate insulator consisting of 30-40 nm thick alicyclic polyimide on high-k metal oxide films leads to a reduction in the operating voltage and the interfacial trap density at the gate insulator interface. The mobility of the FETs was improved from 0.4 to 2.4 cm(2) V-1 s(-1) by thermal annealing of Ph-BTBT-10 at 120 degrees C due to the transition from a monolayer to a bilayer structure and the use of alicyclic polyimide as the polymer gate insulator.

We fabricated inorganic–organic hybrid quantum-dot light-emitting-diodes (QD-LEDs) consisting of several types of solution-processed n-type oxide electron injection layers (EILs)/quantum-dot (QD) and poly (9-vinylcarbazole) (PVK) blend light emitting layer (EMLs)/4,4-bis(carbazole-9yl)bihpheyl (CBP)/a-NPD/1,4,5,8,9, 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) hole injection layer/Al structures. We compared the electrical properties of hybrid QD-LEDs with solution-processed n-type oxide electron injection layers consisting of Al-doped ZnO nano-particles (AZO-NP), polyethyleneimine (PEI), titanium oxide nanosheet (TiO-NS) on PEI (PEI/TiO-NS), and AZO-NP/TiO-NS multilayers. The combination of the PEI dipole layer and ultra-thin TiO-NS nanosheet (∼1 nm) layers reduced the potential barrier at ITO/TiO-NS interface. However, a considerable barrier height of >0.3 eV exists at the TiO-NS/QD interface. The use of small-work function AZO-NP (3.9 eV) effectively improves external quantum efficiency (EQE) compared with relatively large work-function AZO-NP (4.3 eV) and TiO-NS (4.1 eV). The capacitance–voltage curves and the current density–voltage–luminance curves strongly depend on the thickness of the QD:PVK blend (2:1 in weight) layer, and we obtained the optimized thickness for EML as ca. 30 nm. With the improved charge balance and morphology, an EQE of above 3.0% is obtained for green light-emitting QD-LED and an EQE of 0.86% for blue light-emitting QD-LED.

We fabricated multilayered inverted polymer-based LEDs (iPLEDs) consisting of several types of solution-processed electron injection layer (EIL)/F8BT [green light emitting polymer (LEP)] or polyfluorene-based blue LEP (PFO)/TFB (hole-transporting layer)/MoO3/Ag structures. We compared the electrical properties of hybrid iPLEDs with solution-processed hybrid EILs deposited at low temperature (<120 °C) consisting of ZnO/polyethyleneimine (PEI), PEI/tantalum oxide nanosheet (TaO-NS), and PEI/TaO-NS/TmPyPB multilayers. The combination of PEI dipole and ultra-thin TaO-NS (∼1 nm) layers improved the EL efficiency and operating voltages owing to the energy level shift of ∼1 eV and the effective hole blocking at the ITO/TaO-NS/LEP interface. However, a considerable barrier height of >0.5 eV still existed at the TaO-NS/PFO interface. The insertion of electron-transporting small molecules between the TaO-NS and PFO layer effectively reduced the electron injection barrier height and electron transport properties of the multilayered iPLEDs resulting in improved EQE and operating voltage for the blue-light iPLEDs.

We report on the quick deposition technique of the highly oriented 6, 13-bis (trisopropylsilylethynyl) pentacene (TIPS-pentacene) crystalline films from the polystylene (PS)/TIPS-pentacene blend solution onto the oxide dielectric films at an elevated temperature for fabricating organic field-effect transistors (FETs). A vertical phase separation between TIPS-pentacene and PS films on high-k metal oxide films leads to the reduction of operating voltage and the interfacial trap density at the gate insulator interface. The polarized optical microscopy image and in-plane X-ray diffraction analysis suggest the pi-stacking of TIPS-pentacene molecules along the direction parallel to the sweeping direction of meniscus coating. The highly oriented TIPS-pentacene crystalline films were obtained at 0.75–2.0 mm s−1 at 70 °C which was much faster than room temperature (0.01 mm s−1). These effects eventually lead to both the improvement of FET properties and device fabrication processes.