Inkjet printing (IJP) is a versatile technique for realizing high-accuracy patterns in a cost-effective manner. It is considered to be one of the most promising candidates to replace the expensive thermal evaporation technique, which is hindered by the difficulty of fabricating low-cost, large electroluminescent devices, such as organic lightemitting diodes (OLEDs) and quantum dot light-emitting diodes (QLEDs). In this invited review, we first introduce the recent progress of some printable emissive materials, including polymers, small molecules, and inorganic colloidal quantum dot emitters in OLEDs and QLEDs. Subsequently, we focus on the key factors that influence film formation. By exploring stable ink formulation, selecting print parameters, and implementing droplet deposition control, a uniform film can be obtained, which in turn improves the device performance. Finally, a series of impressive inkjet-printed OLEDs and QLEDs prototype display panels are summarized, suggesting a promising future for IJP in the fabrication of large and high-resolution flat panel displays.

•A low turn-on voltage and highly efficient deep red QD-LEDs has been successfully fabricated.•Through thermal treatment, the Von decreases from 4.8 V to 3.6 V and Lmax increases by 60% for single HTL QD-LEDs.•The QD-LEDs with double HTLs exhibits low Von of 1.9 V, high CE and PE of 8.68 cd/A and 10.2 lm/W respectively.Here we reported very bright and highly efficient deep-red quantum dot light-emitting devices (QD-LEDs) with inverted structure by introducing double hole transport layers (HTLs) consisting of 4,4′,4″-tri (N-carbazolyl)-triphenyl-amine (TCTA) and N,N′-bis (naphthalen-1-yl)-N,N′-bis (phenyl)-benzidine (NPB). The turn-on voltage of the optimized device was as low as 1.9 V, the maximum current efficiency and luminance were 8.68 cd/A and 15,000 cd/m2, respectively. However, for the best performance of QD-LED with single hole transport layer, the turn-on voltage reached up to 3.6 V, the peak current efficiency was only 3.84 cd/A and the maximum luminance was 7700 cd/m2. The enhancement of the performance is attributed to the stepwise HTL structure, which can decrease the hole-injection barrier from HTL to QD emitting layer and reduce the turn-on voltage of QD-LEDs. Besides, the lower highest occupied molecular orbital of TCTA can suppress the accumulation of electrons at the interface of QDs/HTL and separate the carrier accumulation zone from the exciton formation interface, which can balance the carriers transportation and enhance performance of QD-LEDs.

Single-emitting-layer (single-EML) hybrid white organic light-emitting diodes (WOLEDs) have attracted a great deal of attention due to their simplified structures. However, the guest concentration is usually too low, which is quite difficult to control and reproduce in the coevaporation process. Herein, for the first time, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine has been used as both the host and the blue emitter in single-EML WOLEDs. By dint of this multifunctional material, the concentration is found to be as high as 1.5%. This device exhibits a maximum total efficiency of 65.3 lm W−1, indicating a significant step towards the real commercialization. Besides, low voltages (i.e., the turn-on voltage is 2.4 V and 3.45 V at 1000 cd m−2) and a color rendering index (CRI) of 77 are obtained for this two-color WOLED. Unlike the working mechanisms in previous single-EML hybrid WOLEDs with low guest concentrations, devices comprising high concentrations exhibit more sophisticated engineering, in which the device smartly allows the utilization of both the fluorescence from the host itself, and the complementary phosphorescence from the guest by incomplete Förster energy transfer, Dexter energy transfer as well as direct exciton formation on the guest. Moreover, we have incorporated this unique host–guest system into a dual-EML hybrid WOLED. Maximum efficiencies of 17.2 lm W−1 and 10.2 lm W−1 at 1000 cd m−2 (3.85 V) with an ultrahigh CRI of 93 are achieved, providing a new opportunity to accomplish the simplified structure/low voltage/high efficiency/ultrahigh CRI trade-off.

•Treating the organic/metal interface with the ether solvent improves the luminance efficiency more than thirty times higher.•The photovoltaic measurements confirm the enhanced efficiency results from the reduction of electron injection barrier.•X-ray photoelectron spectroscopy study reveals that the formation of a carbide-like layer helps the electron injection.•The ethylene oxide functional groups, –CH2CH2O–, reacts with aluminum to form the carbide-like layer.By treating the organic/metal interface between the light emission layer and the cathode with ether solvent, the device performance of the organic light-emitting diodes with aluminum cathode is significantly improved. The maximum luminous efficiency is not only more than thirty times higher than that of the device without any ether solvent treatment, but also higher than the device with regular low work function metal cathode, such as Ba/Al. The enhanced efficiency results from the reduction of electron injection barrier, which is confirmed by the photovoltaic measurements. X-ray photoelectron spectroscopy study reveals that the formation of a carbide-like layer by the reaction between the thermally evaporated aluminum and the ethylene oxide functional group, –CH2CH2O–, helps the electron injection.

•The design of high speed gate driver is optimized by calculation and simulation.•A 20 stages high speed gate driver is fabricated by IZO TFTs process.•A 2.6 μs width pulse can be output at the condition of Rload = 6 kΩ and Cload = 150 pF.•There is a good stability verified by a 48 h test.This paper presents a new bi-side gate driver integrated by indium-zinc-oxide thin film transistors (IZO TFTs). Our optimized operate method can achieve high speed performance by employing a lower duty ratio (25%) CK2 with its pulse located in the middle of the pulse of CK2L to fully use the bootstrapped high voltage of node Q. In addition, the size of devices is optimized by calculation and simulation, and the function of the proposed gate driver is predicted by the circuit simulation. Furthermore, the proposed gate driver with 20 stages is fabricated by the IZO TFTs process. It is shown that a 2.6 μs width pulse with good noise-suppressed characteristic can be successfully output at the condition of Rload = 6 kΩ and Cload = 150 pF. The power consumption of the proposed gate driver with 20 stages is measured as 1 mW. Hence, the proposed gate driver may be applied to the display of 4K resolution (4096 × 2160) at a frame rate of 120 Hz. Moreover, there is a good stability for the proposed gate driver under 48 h operation.

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.

•A family of aminoalkyl-functionalized blue-, green- and red-emitting polyfluorene derivatives were synthesized.•The aminoalkyl-functionalized copolymers exhibited dual functions of efficient light emission and electron injection.•Device performances can be optimized by varying the molar ratios of the incorporated aminoalkyl side groups.A family of aminoalkyl functionalized blue-, green- and red-emitting polyfluorene based copolymers were synthesized by Suzuki copolymerization. Dibenzothiophene-S,S-dioxide-3,7-diyl (FSO), 2,1,3-benzothiadiazole (BT) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were incorporated into the backbone of copolymers as blue, green and red chromophores, respectively. It was realized that for all these aminoalkyl functionalized copolymers, the thermal stabilities, UV–vis absorption and electrochemical properties are not affected by molar ratio of aminoalkyl side groups. However, the increased amino-groups content can induce the formation of excimer in FSO based blue-emitting copolymer, which in turn leaded to broadened photoluminescence and electroluminescence spectra along with decreased emission efficiency. In contrast, device based on green and red-emitting copolymers exhibited stable emission, and device performance improved progressively with the enhanced content of aminoalkyl co-monomers. Comparing to the copolymers without aminoalkyl side chains, aminoalkyl functioned materials exhibited distinctly improved device performances for the application as emissive layer in light emitting diodes using high work-function Al as cathode due to the formation of interfacial dipoles that can facilitate electron injection. The maximum luminous efficiency of 3.28, 7.31 and 0.79 cd A−1 was achieved based on copolymers BFN1, GFN15 and RFN15, respectively with device architecture of ITO/PEDOT:PSS/PVK/copolymer/Al. These results indicate that aminoalkyl functionalized copolymers can have great potential for the application as efficient light-emitting layer with high work-function/air-stable cathode.Graphical abstract

A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.

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.

Single-emitting-layer (single-EML) hybrid white organic light-emitting diodes (WOLEDs) have attracted a great deal of attention due to their simplified structures. However, the guest concentration is usually too low, which is quite difficult to control and reproduce in the coevaporation process. Herein, for the first time, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine has been used as both the host and the blue emitter in single-EML WOLEDs. By dint of this multifunctional material, the concentration is found to be as high as 1.5%. This device exhibits a maximum total efficiency of 65.3 lm W−1, indicating a significant step towards the real commercialization. Besides, low voltages (i.e., the turn-on voltage is 2.4 V and 3.45 V at 1000 cd m−2) and a color rendering index (CRI) of 77 are obtained for this two-color WOLED. Unlike the working mechanisms in previous single-EML hybrid WOLEDs with low guest concentrations, devices comprising high concentrations exhibit more sophisticated engineering, in which the device smartly allows the utilization of both the fluorescence from the host itself, and the complementary phosphorescence from the guest by incomplete Förster energy transfer, Dexter energy transfer as well as direct exciton formation on the guest. Moreover, we have incorporated this unique host–guest system into a dual-EML hybrid WOLED. Maximum efficiencies of 17.2 lm W−1 and 10.2 lm W−1 at 1000 cd m−2 (3.85 V) with an ultrahigh CRI of 93 are achieved, providing a new opportunity to accomplish the simplified structure/low voltage/high efficiency/ultrahigh CRI trade-off.