Bicolour, large area, inkjet-printed metal halide perovskite light emitting diodes.

We demonstrate a bicoloured metal halide perovskite (MHP) light emitting diode (LED) fabricated in two sequential inkjet printing steps. By adjusting the printing parameters, we selectively and deliberately redissolve and recrystallize the first printed emissive layer to add a pattern emitting in a different color. The red light emitting features (on a green light emitting background) have a minimum size of 100 µm and originate from iodide-rich domains in a phase-segregated, mixed MHP. This phase forms between the first layer, a bromide-based MHP, which is partially dissolved by printing, and the second layer, an iodide-containing MHP. With an optimised printing process we can retain the active layer integrity and fabricate bicolour, large area MHP-based LEDs with up to 1600 mm2 active area. The two emission peaks at 535 nm and 710 nm are well separated and produce a strong visual contrast.

Doubly Bridged Anthracenes: Blue Emitters for OLEDs.

The photooxidative stability of a series of doubly bridged anthracenes was evaluated after their preparation via twofold macrocyclization of a bis(resorcinyl)anthracene. Lightfastness correlates with the energy levels of the highest occupied molecular orbital (HOMO), resulting in superior stability of the tetraesters compared to the tetraethers. The lengths and steric demand of the linker only plays a minor role for the ester-based compounds, which can be prepared in reasonable yields and thus tested in proof-of-concept organic light-emitting diodes. Double ester-bridging allows deep blue electro-luminescence, highlighting the importance of the choice of the functional groups used for macrocyclization.

Large area inkjet-printed metal halide perovskite LEDs enabled by gas flow assisted drying and crystallization.

We demonstrate the upscaling of inkjet-printed metal halide perovskite light-emitting diodes. To achieve this, the drying process, critical for controlling the crystallization of the perovskite layer, was optimized with an airblade-like slit nozzle in a gas flow assisted vacuum drying step. This yields large, continuous perovskite layers in light-emitting diodes with an active area up to 1600 mm2.

High performance organic light-emitting diodes employing ITO-free and flexible TiO x /Ag/Al:ZnO electrodes.

The broad application of flexible optoelectronic devices is still hampered by the lack of an ITO-free and highly flexible transparent electrode. Dielectric/metal/dielectric (DMD) transparent electrodes are promising candidates to replace ITO, especially in flexible devices due to their mechanical stability to bending, high optical transmittance and low sheet resistance (<6 Ω sq-1). This paper reports on organic light emitting diodes (OLEDs) employing a DMD electrode, specifically TiO x /Ag/Al:ZnO (doped with 2 wt% Al2O3) fabricated by sputter deposition, together with a solution-processed organic polymeric emitting layer. The electrodes were sputtered without substrate heating on rigid glass and flexible polyethylene terephthalate (PET). The results showed that the OLED devices on the DMD electrodes outperform the OLEDs on commercial ITO substrates in terms of maximum luminance as well as current efficacy. Specifically, DMD-based devices achieve up to 30% higher current efficacy on glass and up to 260% higher efficacy on PET, as compared to the ITO-based reference devices. Maximum luminance reaches up to 100 000 cd m-2 for the DMD-based OLEDs on glass and 43 000 cd m-2 for those on PET. This performance is due to the low sheet resistance of the electrodes combined with efficient light outcoupling and shows the potential of DMDs to replace ITO in optoelectronic devices. This outstanding type of optoelectronic device paves the way for the future high throughput production of flexible display and photovoltaic devices.

Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols.

High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3 interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.

High-Performing Polycarbazole Derivatives for Efficient Solution-Processing of Organic Solar Cells in Air.

The application of conjugated materials in organic photovoltaics (OPVs) is usually demonstrated in lab-scale spin-coated devices that are processed under controlled inert conditions. Although this is a necessary step to prove high efficiency, testing of promising materials in air should be done in the early stages of research to validate their real potential for low-cost, solution-processed, and large-scale OPVs. Also relevant for approaching commercialization needs is the use of printing techniques that are compatible with upscaling. Here, solution processing of organic solar cells based on three new poly(2,7-carbazole) derivatives is efficiently transferred, without significant losses, to air conditions and to several deposition methods using a simple device architecture. High efficiencies in the range between 5.0 % and 6.3 % are obtained in (rigid) spin-coated, doctor-bladed, and (flexible) slot-die-coated devices, which surpass the reference devices based on poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT). In contrast, inkjet printing does not provide reliable results with the presented polymers, which is attributed to their high molecular weight. When the device area in the best-performing system is increased from 9 mm(2) to 0.7 cm(2), the efficiency drops from 6.2 % to 5.0 %. Photocurrent mapping reveals inhomogeneous current generation derived from changes in the thickness of the active layer.

Knowledge-based development of a nitrate-free synthesis route for Cu/ZnO methanol synthesis catalysts via formate precursors.

High-performance Cu/ZnO/(Al(2)O(3)) methanol synthesis catalysts are conventionally prepared by co-precipitation from nitrate solutions and subsequent thermal treatment. A new synthesis route is presented, which is based on similar preparation steps and leads to active catalysts, but avoids nitrate contaminated waste water.