Yubin Xiao

Low-temperature facile solution-processed gate dielectric for combustion derived oxide thin film transistors

In this work, acetylacetone assisted solution-processed In–Ga–Zn–O (IGZO) thin film transistors (TFTs) using Al2O3 as gate dielectrics were investigated. Normally, fully covered Al2O3 thin films are difficult to achieve by spin coating with conventional solvent, such as 2-methoxyethanol, due to the poor wettability of highly doped silicon. Here, a conventional aluminum nitrate solution with an additive was designed to spin coat robust continuous Al2O3 thin films, resulting from improved solution hydrophilic with a contact angle of 17°. For active layer fabrication, we utilized the previous reported combustion process to lower treatment temperature, which could be confined in the range from 220 °C to 300 °C, without losing the device performance. Results show that all the devices performed well. Especially, after 240 °C annealing of both Al2O3 (in thickness of around 45 nm) and IGZO thin films (in thickness of around 30 nm), we have obtained the following device parameters, namely a Al2O3 dielectric breakdown electric field at 7.8 MV cm−1, a current density of around 1 × 10−6 A cm−2 in the voltage range of −3 V to 3 V, a areal capacitance of 291 nF cm−2 at 100 Hz, a carrier mobility of 0.74 cm2 V−1 s−1, a threshold voltage of −0.4 V, a current on–off ratio of 6 × 103, a subthreshold swing of 375 mV per decade. Fabrication of combustion-processed active layers and our facile solution processed high-k dielectrics provides a feasible approach for low cost oxide flexible TFTs applications.

Ternary blend bulk heterojunction photovoltaic cells with an ambipolar small molecule as the cascade material

Here we demonstrate that the power conversion efficiency of a P3HT:PC61BM bulk heterojunction solar cell can be improved from 3.4% to 4.3% by adding 10% of a cyclopent[hi]aceanthrylene derivative (CPA), which is an ambipolar small-molecule semiconductor, to form a ternary blend BHJ solar cell. This enhanced power conversion efficiency arises from improvement of both short-circuit current and open-circuit voltage because the addition of CPA not only provides absorption complementary to that of P3HT, but also leads to longer charge carrier lifetime in the bulk heterojunction.

Derivitization of pristine graphene for bulk heterojunction polymeric photovoltaic devices

In this communication, we report a simple method for a covalent band-forming reaction to change the hybridization of carbon atoms from sp2 to sp3, to introduce a band gap in pristine graphene. Graphene with well-defined functionality was synthesized, and the resulting material was soluble in organic solvent. The LUMO of functionalized graphene was below the LUMO of poly(3-hexylthiophene) (P3HT) and close to that of [6,6]-phenyl C61-butyric acid methyl ester (PCBM), indicating its suitability as an electron acceptor for organic photovoltaic (OPV) applications. We further show the P3HT/functionalized graphene composite as the active layer in a solar cell, with device efficiency of 1.1%.

Oxygen plasma assisted high performance solution-processed Al2Ox gate insulator for combustion-processed InGaZnOx thin film transistors

The effects of oxygen-plasma treatment on solution-processed Al2Ox gate dielectrics for InGaZnOx (IGZO) thin film transistors (TFTs) are investigated in this paper. Thin films of amorphous Al2Ox are successfully fabricated by annealing temperature of 300 °C. Utilizing oxygen-plasma treated gate dielectrics, combustion-processed IGZO TFTs, which are annealed at a temperature of 300 °C, show a mobility of 7.3 cm2 V−1 s−1, a threshold voltage of −0.3 V, an on-off current ratio of 1 × 105, a subthreshold swing of 160 mV/decade, when operating with a voltage ranging from −2 V to +5 V. Our experimental results demonstrate that oxygen-plasma treatment can remarkably improve dielectric performance. This is presumably due to the passivation of interfacial and bulk traps, and the reduced concentration of oxygen vacancies.

Solution-processed PCDTBT capped low-voltage InGaZnOx thin film phototransistors for visible-light detection

The effects of visible-light detection based on solution processed poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole) (PCDTBT) capped InGaZnOx (IGZO) phototransistors with Al2Ox serving as gate dielectric are investigated in this paper. The high-k dielectric is used to lower the device operating voltage down to 2 V. Photons emitted from laser sources with the wavelengths (λ) of 532 nm and 635 nm are absorbed through the layer of PCDTBT to generate electron-hole-pairs (EHPs). After the separation of EHPs, electrons are injected into IGZO layer through the p-n junction formed between the IGZO (n-type semiconductor) and the PCDTBT (p-type semiconductor). The photo-generated carriers boost the drain current of the transistors as well as bring about the negative threshold voltage shift. Significant enhanced detection performance is achieved under the laser wavelength of 532 nm. The highest photoresponsivity reaches up to 20 A/W, while the photoresponse rise time comes ...

Low-voltage graphene field-effect transistors based on octadecylphosphonic acid modified solution-processed high-k dielectrics

In this study, a solution-processed bilayer high-k dielectric (Al2O(y)/TiO(x), abbrev. as ATO) was used to realize the low-voltage operation of graphene field-effect transistors (GFETs), in which the graphene was grown by atmospheric pressure chemical vapor deposition (APCVD). Upon modifying the interface between graphene and the dielectric by octadecylphosphonic acid (ODPA), outstanding room-temperature hole mobility up to 5805 cm(2) V(-1) s(-1) and electron mobility of 3232 cm(2) V(-1) s(-1) were obtained in a small gate voltage range from -3.0 V to 3.0 V under a vacuum. Meanwhile, an excellent on/off current ratio of about 8 was achieved. Our studies demonstrate an effective route in which utilizing the low-temperature solution-processed dielectrics can achieve low-voltage and high performance GFETs.