Monthly Archives: July 2014

Degradation study and calculation of density-of-states in PTCDI-C8 channel layer from the electrical characteristics of thin-film transistors

N-type organic thin film transistor (OTFT) with a top-contact structure was fabricated by thermal vapour deposition using N,N′-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as an n-channel layer on Si/SiO2 substrate. The density of localised states (DOS) in the gap of PTCDI-C8 is estimated by studying the temperature dependence of the electrical characteristics of OTFT. The measurements were done immediately after the devices fabrication (non-degraded devices) and also after 2 h of exposure to air (degraded devices). The extracted field effect mobility decreased from 0.02 to 0.004 cm2 V−1 s−1 and threshold voltage increased from 25.3 to 40.5 V for the degraded OTFT. The degradation of OTFTs was due to the trapping of majority charge carriers in the localised trap states created by adsorbed oxygen in the PTCDI-C8 layer. These localised trap states were found to be situated at around 0.15 eV above the lowest unoccupied molecular orbit level. The study of DOS in OTFTs gives a complete understanding of trap-limited transport in organic thin film semiconductors.

Enhancing charge transport in copper phthalocyanine thin film by elevating pressure of deposition chamber

Publication date: August 2014 Source:Organic Electronics, Volume 15, Issue 8 Author(s): Qi Liu , Yi Li , Xingyong Wang , Wei Huang , Jing Ma , Yun Li , Yi Shi , Xizhang Wang , Zheng Hu Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (P dep) (ranging from 1.8×10−4 Pa to 1.0×10−1 Pa). The transistor performance highly depended on P dep. A field-effect mobility of 2.1×10−2 cm2/(Vs) was achieved under 1.0×10−1 Pa. Detailed investigations revealed that P dep modulates the molecular packing and orientation of the organic films grown on a SiO2/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when P dep increased, which was beneficial in reducing energy consumption. Graphical abstract Highlights

Direct growth of large-area graphene films onto oxygen plasma-etched quartz for nitrogen dioxide gas detection

We report a simple oxygen plasma-etching of quartz substrates as an active surface for efficient growth of graphene films through a chemical vapour deposition process. The resulting graphene films prepared on the oxygen plasma-etched quartz surface exhibited a high optical transmittance of 95.3% coupled with a sheet resistance of ∼4.6 kΩ sq −1 . We also demonstrated that the as-grown graphene films had a high sensitivity to NO 2 at low parts-per-million level in air at room temperature. Our work suggested that the as-grown films on quartz can be used as chemoresistive sensors for transparent electronics applications.