Low-voltage pentacene-based organic thin film transistors (OTFTs) are fabricated with solution-process hafnium oxide (HfO<sub>2</sub>) as gate dielectric layer. The dielectric high-k HfO<sub>2</sub> film was deposited from the sol-gel solution prepared by dissolving HfCl<sub>4</sub>(98%, Sigma-Aldrich) in ethanol at a proper concentration. We have investigated the effects of the insulating layer on device. As a result, the device with only HfO<sub>2</sub> gate dielectric exhibited a good performance with a threshold voltage of -0.88 V, a sub-threshold swing of 1.12 V/dec, and a high field-effect mobility of 1×10<sup>-3</sup> cm<sup>2</sup>/Vs. After employing a very thin PMMA film onto HfO<sub>2</sub>, the performance of the devices with bilayer dielectrics shows a great improvement. The mobility of these OTFTs can be further boost up to 1.2×10<sup>-2</sup> cm<sup>2</sup>/Vs, and the sub-threshold swing reduced to 0.77 V/dec and the drain current on/off ratio increased almost 7 times. The PMMA insulator buffer layer can also effectively reduce gate leakage current. The results demonstrate that an appropriate polymer buffer layer is a favorable way to improve the performance of the OTFTs with good electrical stability.
White organic light-emitting devices (WOLEDs) with a novel direct hole-injection structure based on the hole transport capability of bis[2-(4-tert-butylphenyl) benzothiazolato-N,C2'] iridium(acetylacetonate) [(t-bt)2I-r(acac)] were fabricated. By inserting an electron-blocking layer, we successfully manipulated electron transport and achieved white light emission. A maximum luminance of 26020 cd/m2, a maximum current efficiency of 22.37 cd/A and a maximum power efficiency of 18.99 lm/W were obtained. This novel structure can significantly simplify the production processes of WOLEDs and deserves further investigation.