Linfeng Lan

High-performance polymer heterojunction solar cells of a polysilafluorene derivative

High-performance polymer heterojunction solar cells fabricated from an alternating copolymer of 2,7-silafluorene (SiF) and 4,7-di(2′-thienyl)-2,1,3-benzothiadiazole (DBT) (PSiF-DBT) as the electron donor blended with [6,6]-phenyl-C61-butyric acid methyl ester as the electron acceptor were investigated. A power-conversion efficiency up to 5.4% with an open-circuit voltage of 0.90V, a short-circuit current of 9.5mAcm−2, and a fill factor of 50.7% was achieved under the illumination of AM 1.5G from a calibrated solar simulator (800Wm−2). The field-effect transistors fabricated from PSiF-DBT showed a high hole mobility of ∼1×10−3cm2V−1s−1.

Low Band‐Gap Conjugated Polymers with Strong Interchain Aggregation and Very High Hole Mobility Towards Highly Efficient Thick‐Film Polymer Solar Cells

Absorption spectra of polymer FBT-Th4 (1,4) (M n = 46.4 Kg/mol, E g = 1.62 eV, and HOMO = -5.36 eV) indicate strong interchain aggregation ability. High hole mobilities up to 1.92 cm(2) (V s)(-1) are demonstrated in OFETs fabricated under mild conditions. Inverted solar cells with active layer thicknesses ranging from 100 to 440 nm display PCEs exceeding 6.5%, with the highest efficiency of 7.64% achieved with a 230 nm thick active layer.

High performance indium-zinc-oxide thin-film transistors fabricated with a back-channel-etch-technique

Indium-zinc-oxide thin-film transistors (TFTs) with back-channel-etch (BCE) structure were demonstrated. A stacked structure of Mo/Al/Mo was used as the source/drain electrodes and patterned by a wet-etch-method. Good etching profile with few residues on the channel was obtained. The TFT showed a field effect mobility of 11.3 cm2 V−1 s−1 and a sub-threshold swing of 0.24 V/decade. The performance of this kind of TFT was better than that of the TFT with etch-stopper-layer structure, which was proved to be due to the lower contact resistance. The BCE-TFTs fabricated with this method have good prospect due to the advantage of low cost.

A flexible AMOLED display on the PEN substrate driven by oxide thin-film transistors using anodized aluminium oxide as dielectric

We report a flexible AMOLED display driven by oxide thin film transistors (TFTs) with anodic AlOx gate dielectric on a polyethylene naphthalate (PEN) substrate with a process temperature below 150 °C. The TFTs exhibit a field-effect mobility of 12.87 cm2 V−1 s−1, a subthreshold swing of 0.20 V dec−1, and an Ion/Ioff ratio of 109.

Low-Voltage High-Stability Indium–Zinc Oxide Thin-Film Transistor Gated by Anodized Neodymium-Doped Aluminum

Neodymium-doped aluminum (Al-Nd) was used as a gate electrode and was anodized, forming a layer of Nd:Al2O3 as the dielectric for indium-zinc oxide (IZO) thin-film transistors (TFTs). The Nd:Al2O3 showed high capacitance (110 nF/cm2), high breakdown field (>;6 MV/cm), and low leakage current (<; 10-7 A/cm2 at 2.0 MV/cm) without hillocks when annealed at 300°C. The TFT showed a low operating voltage of 3 V, a low off current of ~10-13 A, a high mobility of 13.7 cm2 · V-1 · s-1, and excellent electrical stability because of the good interface coupling between Nd:Al2O3 and IZO, resulting from the low electronegativities of Al and Nd.

Efficient hybrid white organic light-emitting diodes with extremely long lifetime: the effect of n-type interlayer

The effect of n-type interlayer in hybrid white organic light-emitting diodes (WOLEDs) has been systematically investigated by using various n-type materials. A new finding, that the triplet energy rather than electron mobility or hole-blocking ability of interlayer plays a more positive role in the performance of hybrid WOLEDs, is demonstrated. Based on the new finding, a more efficient n-type interlayer bis[2-(2-hydroxyphenyl)-pyridine] beryllium has been employed to realize a high-performance hybrid WOLED. The resulting device (without n-doping technology) exhibits low voltages (i.e., 2.8 V for 1 cd/m2, 3.9 V for 100 cd/m2) and low efficiency roll-off (i.e., 11.5 cd/A at 100 cd/m2 and 11.2 cd/A at 1000 cd/m2). At the display-relevant luminance of 100 cd/m2, a total power efficiency of 16.0 lm/W, a color rendering index of 73 and an extremely long lifetime of 12596265 h are obtained. Such superior results not only comprehensively indicate that the n-type materials are effective interlayers to develop high-performance hybrid WOLEDs but also demonstrate a significant step towards real commercialization in WOLEDs.

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors

Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InOx semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm(2) V(-1) s(-1) and an on/off ratio of larger than 10(9). This approach of fabricating short-channel TFTs by inkjet printing will promote the large-area fabrication of short-channel TFTs in a cost-effective manner.

InGaZnO thin-film transistors with back channel modification by organic self-assembled monolayers

InGaZnO (IGZO) thin-film transistors (TFTs) with back channel modified by different kinds of self-assembled monolayers (SAMs) were fabricated. The mobility and electrical stability of the IGZO-TFTs were greatly improved after SAM-modification, owing to the good interface coupling and less water adsorption-desorption effect on the IGZO surface. Meanwhile, the octadecyltriethoxysilane (OTES) treated IGZO-TFT exhibited a higher mobility of 26.6 cm2 V−1 s−1 and better electrical stability compared to the octadecanethiol (ODT) treated one, which was attributed to the formation of a more compact and steady SAM on the IGZO surface after OTES treatment.

Influence of source and drain contacts on the properties of the indium-zinc oxide thin-film transistors based on anodic aluminum oxide gate dielectrics

Thin-film transistors (TFTs) based on indium-zinc oxide (IZO) active layer and anodic aluminum oxide (Al2O3) gate dielectric layer were fabricated. The influence of source and drain (S/D) contacts on TFT performance was investigated by comparing IZO–TFTs with different S/D electrodes. The TFT with Mo S/D electrodes had higher output current and lower threshold voltage, but had poorer subthreshold swing and lower effective electron mobility compared to that with ITO S/D electrodes. By using x-ray photoelectron spectroscopy (XPS) depth profile analyzing method, it was observed that Mo was diffusing seriously into IZO, resulting in the variation of the effective channel length, thereby causing serious short-channel effect, poor subshreshold swing, and bad uniformity of the TFTs with Mo S/D electrodes.

Wide bandgap dithienobenzodithiophene-based π-conjugated polymers consisting of fluorinated benzotriazole and benzothiadiazole for polymer solar cells

Two wide bandgap donor–acceptor type π-conjugated polymers based on dithienobenzodithiophene as the donor unit and difluorobenzotriazole or difluorobenzothiadiazole as the acceptor unit were designed and synthesized. The copolymer based on difluorobenzothiadiazole exhibited more pronounced aggregations in chlorobenzene solutions than that of the copolymer based on difluorobenzotriazole. Both copolymers exhibited relatively wide bandgaps with deep highest occupied molecular orbitals, leading to high open circuit voltages of over 0.95 V for the fabricated polymer solar cells. These copolymers exhibited quite analogous hole mobility of about 0.1 cm2 V−1 s−1 as measured by organic field effect transistors. Bulk heterojunction polymer solar cells based on these copolymers as the electron-donating materials and PC71BM as the electron-accepting material exhibited relatively high performance, with the best power conversion efficiency of 7.45% attained for the copolymer based on the difluorobenzothiadiazole unit. These results demonstrated that the constructed wide bandgap π-conjugated polymers can be promising candidates for the fabrication of high performance solar cells with multi-junction architectures.