Finally, inkjet printed metal halide perovskite LEDs utilizing seed crystal templating of salty PEDOT PSS

Solution processable metal halide perovskites are increasingly implemented in perovskite based light emitting diodes PeLEDs . Especially green PeLEDs based on methylammonium lead bromide MAPbBr3 composites exhibit impressive optoelectronic properties, while allowing processing by low cost and upscalable printing methods. In this study, we have investigated the influence of potassium chloride KCl blended into the common hole injection material poly 3,4 ethylenedioxythiophene polystyrene sulfonate PEDOT PSS to boost PeLED device performance. The inclusion of KCl firstly results in a change in morphology of the PEDOT PSS layer, which then acts as a template during deposition of the perovskite layer. A MAPbBr3 polyethylene glycol PEG composite was used, which does not require the deposition of an anti solvent droplet to induce preferential perovskite crystallization and is therefore suitable for spin coating and scalable inkjet printing processes. PeLEDs utilizing the KCl induced templating effect on a planar PEDOT PSS MAPbBr3 PEG architecture show improved performance, predominantly due to improved crystallization. PeLEDs incorporating spin coated perovskite layers yield a 40 fold increase in luminance 8000 cd m 2 while the turn on voltage decreases to 2.5 V. KCl modified PEDOT PSS contact layers enabled the realization of inkjet printed PeLEDs with luminance increased by a factor of 20 at a maximum of 4000 cd m 2 and a turn on voltage of 2.5 V. This work paves the way for inkjet printed perovskite light emitting devices for a wide variety of low cost and customizable application

Gas flow assisted vacuum drying Identification of a novel process for attaining high quality perovskite films

Controlling the nucleation and crystal growth in solution processed metal halide perovskite MHP thin films is the pivotal point in fabricating homogenous and pinhole free films. Using scalable coating and printing techniques, vacuum and gas flow assisted drying processes turn out to be the most promising methods to induce nucleation and crystallization. Yet, the exact interplay and nature of these processes are unclear. In our work, we optically monitor these processes in situ. For the first time, we can show that a controlled venting of the vacuum chamber and the use of a subsequent gas flow are key to achieve homogenous nucleation. Utilizing this gas flow assisted vacuum drying process, we find that regular, optically dense and pinhole free MHP layers can be fabricated via inkjet printing, which yield solar cells with a power conversion efficiency of 16 , as compared to 4.5 for vacuum dryin

Combinatorial inkjet printing for compositional tuning of metal halide perovskite thin films

To accelerate the materials discovery and development process for a sustainable technology advancement it is imperative to explore and develop combined high throughput material synthesis and analysis workflows. In this work, we investigate a method of combinatorial inkjet printing to tune the composition of the inorganic cesium lead mixed halide perovskite solid solution, CsPb BrxI1 amp; 8722;x 3. The compositional variation is achieved by simultaneous printing of different precursor inks with multiple printheads and controlled by varying the number of droplets printed by each printhead throughout the sample. The droplet placement is optimised through an algorithm that allows maximum mixing of the combined inks. The local compositional homogeneity of thin film samples was investigated as a function of the printing resolution by micrometer resolution X ray fluorescence and synchrotron based grazing incidence wide angle X ray scattering. We show that a combinatorial library of ten compositions between CsPbI3 and CsPbBr2I, printed using the developed algorithm, is locally homogeneous for the optimised printing parameters. An implementation of the algorithm in the high level programming language Python is provided for easy use in other system

An open-access database and analysis tool for perovskite solar cells based on the FAIR data principles

Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42, 400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences. © 2021, The Author(s)

A guide to qualitative haze measurements demonstrated on inkjet printed silver electrodes for flexible OLEDs

The search for alternative transparent electrodes to the commonly used indium tin oxide ITO in optoelectronic devices has led to solution based approaches based on inkjet printing. As an additive manufacturing technique that allows drops to be positioned only where necessary, inkjet printing shows reduced waste of starting material compared to other methods such as spin coating. As a result, functional materials can be both coated and structured without the need for masks or lithographic pre patterning of the substrate. For this contribution, we utilized a particle free silver ink to produce a transparent electrode by inkjet printing. After printing, the silver ions were reduced to metallic silver by an argon plasma. The process takes place at low temperatures ca. 40 50 C , making it suitable for use with flexible substrates, which are often temperature sensitive. The printed silver layers show good electrical conductivity and optical transmittance, with a crystalline grain structure being formed and maintained during the metallization process. This structure forms a self organized nanometer size grid, whose structure allows light to pass through. Due to its nano structured property, the haze of the electrode was investigated using a simple experimental setup based on a light source shining through the electrode and analyzing the size of the projected pattern. Such qualitative assessment can be a useful indication of the quality of the electrode and we provide details on how to replicate this setup. The final electrodes were implemented in solution processed OLEDs, which showed bright luminance and overall low haze compared to ITO based reference device