Multilayer OLEDs with four slot die-coated layers

For the first time, multilayer OLEDs with four solution-processed layers are fabricated step-bystep using slot die coating. A suitable choice of coating parameters and fluid formulation enables the application of different material classes as large-area homogeneous layers with thicknesses in the nanometer range. The AFM measurements of the slot die-coated layers consisting of small molecules showed Ra values of 0.21-0.28 nm, less than previously reported in the literature. Based on a two-layer reference OLED consisting of a HIL and EML, the stack architecture is first extended by a crosslinked HTL. These threelayer OLEDs with a crosslinked HTL achieve 70% higher efficiency, compared to that of the reference devices, thus assuming successfully separated layers. In a further step, an additional ETL is applied via the orthogonal solvent approach to obtain four solutionprocessed layers. The averaged power efficiency of the four-layer OLEDs is increased by a factor of 2.2 compared to the reference OLEDs up to a value of 3.5 lm/W. Based on these results, it can be assumed that both approaches, the use of orthogonal solvents as well as the application of crosslinkable materials, have been successfully combined to fabricate multilayer OLEDs with four separated slot die-coated layers

Comparative Study of Printed Multilayer OLED Fabrication through Slot Die Coating, Gravure and Inkjet Printing, and Their Combination

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N '-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N '-bis(4-methoxyphenyl)biphenyl-4,4 '-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A(-1) is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance

Comparative Study of Printed Multilayer OLED Fabrication through Slot Die Coating, Gravure and Inkjet Printing, and Their Combination

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N′-bis(4-methoxyphenyl)biphenyl-4,4′-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A⁻¹ is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance

Weed Dynamics and Management in Wheat

Wheat is among the most important cereal and food crops of world and is grown in almost all parts of the world. It is a staple for a large part of the world population. Any decline in wheat yield by biotic or abiotic factors may affect global food security adversely. Weeds are the most damaging pest of wheat causing in total 24% losses in wheat grain yield. In this chapter, we discuss the (i) weed flora in different wheat growing regions of world; (ii) the yield losses caused by weeds in wheat; (iii) the preventive and cultural options for weed management; (iv) physical weed control;(v) chemical weed control; and (vi) integrated weed management strategy in wheat. A critical analysis of recent literature indicated that broadleaved weeds are the most common group of weeds in wheat fields followed by grass weeds, while sedges were rarely noted in wheat fields. Across the globe, the most important weeds in wheat fields were Avena fatua L., Chenopodium album L., Phalaris minor Retz., Galium aparine L., Stellaria media (L.) Vill., and Veronica persica Poir., respectively. Adoption of wise weed management strategies may help control weeds and avoid yield losses. Both preventive measures and cultural practices have proved their significance for improving weed control in wheat; physical and chemical tools are the other options. Moreover, site-specific herbicide application may help to make weed control economical and reduce the herbicide input. Nonetheless, integrated strategies should be opted for effective and ecofriendly weed management in wheat

Agroecological weed control using a functional approach: a review of cropping systems diversity

International audienceAgriculture since the 1950s has shown pronounced trends toward specialisation and intensification. Intensive measures have been taken for crop protection against pests through the widespread use of chemical pesticides in order to reduce the loss of agriculture yield. Although crop protection practices have reduced the overall potential losses of 50 % to actual losses of about 30 %, crop losses due to pests still vary from 14 to 35 % according to the country. Moreover, consequences of this intensive agriculture are now well known with an important increase of atmospheric CO2 concentrations, water pollution and biodiversity loss. Current challenge is thus to design alternative sustainable cropping systems which maintain food production while reducing externalities. Application of ecological principles to agroecosystems has been proposed for that purpose. Nonetheless, it is difficult since crop systems are characterised by frequent and high disturbances, high nutrient input and high pressure of human activities. Here, we review the current knowledge in weed science and functional ecology and propose a conceptual framework to analyse weed community assembly in arable fields. Cropping systems are highly variable in their combination of agricultural techniques. We designed a trait-based approach of functional diversity (1) to establish a comparative description of the environmental gradients created by cropping systems and (2) to characterise the response of weeds to environmental gradients. We categorise the effects of cropping systems on the environment into disturbance and resource gradients. Disturbances induced by actual and previous agricultural practices are split into physical and chemical components, whose regime are defined by disturbance timing and frequency. Resource availability in arable fields is described by the value of effect traits of crops, such as plant height, that are related to their use of resources. Finally, we provide a list of relevant response traits of weeds to each component of the two gradients