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Large area metal halide perovskite LEDs were fabricated by inkjet printing. Homogeneous drying and crystallization was facilitated by a guided and optimized gas flow.

In this work, we rationalize the chemical pathways and kinetics of the crystallization of methylammonium lead iodide hybrid perovskite. Our approach includes a combination of analysis of solvent coordination, the structure of intermediate solvate phases, and modeling evaporation rates of precursor solutions. The evolution of solution species via intermediate solvate phases and into perovskite thin films during drying was monitored by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). All studied precursor solutions exhibited the formation of intermediate solvate phases including a previously unreported GBL phase. In single-solvent solutions, crystallization kinetics are determined by the solvent evaporation rate and saturation concentration required for nucleation. In binary solvent mixtures, the evaporation rate of solutions is dominated by the most volatile solvent which leads to unequal evaporation of the components of the mixture. The structure of the intermediate phases in such systems strongly depends on the coordination strength and the availability of solvents upon nucleation. The combined approach described in this work allows predicting the kinetics and the chemical pathways of crystallization of hybrid perovskites in complex solvent mixtures. This insight is of great importance for future perovskite ink design.

In this communication, we present the phase diagram of CsPb BrxI1 amp; 8722;x 3 0 amp; 8804; x amp; 8804; 1, 300 585 K obtained by high throughput in situ GIWAXS measurements of a combinatorial thin film library. We find that all compositions convert to the cubic perovskite phase at high temperature and that the presence of bromide in the films stabilizes the metastable perovskite phases upon cool down. In accordance with recent predictions from DFT calculations, the transition temperatures monotonically decrease with increasing bromide content

Silver particle free inks display immense superiority and potential over silver nanoparticle based inks in the aspect of synthesis, flexibility and low temperature processing, which has attracted considerable research interest as an alternative for fabricating conductive structures in recent years. Although recent research on silver particle free inks has led to beneficial results, there are still some drawbacks some of the inks are chemically unstable and hence are not suitable for industrial inkjet printing process, although they have good conductivity; while others are cheap in terms of raw material costs but are complicated to make due to the complex synthetic route or using hazardous procedures, or are not compatible with inkjet printing. Therefore, it will be advantageous to develop a stable, cheap and inkjet printable silver particle free ink using a simple synthetic procedure. Alcohols are favorable solvents for silver particle free inks that can provide the ink with essential fluid properties for inkjet printing. However, they have some negative effects on the ink performance due to their physicochemical properties, which should be avoided. In this work, a simple do it yourself silver particle free ink is presented, which shows high chemical stability, low cost and good printability. The ink is formulated via a simple silver oxalate precursor route in alcohols. The fluid property, thermal property, stability and electrical performance of the inks based on different alcohols were investigated and optimized to obtain the final ink for printing on glass and flexible polyimide substrates. The printed Ag features yielded a resistivity of 15.46 amp; 956; amp; 937; cm at a sintering temperature of 180 C, which is equivalent to 10 times bulk silver. Based on a comprehensive assessment, we can offer a low cost, easy to make, reliable and highly competitive ink for flexible printed electronics

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 applications

Solar cells based on metal-halide perovskite semiconductors inspire high hopes for efficient low cost solar cell technology. This material class exhibits a facile tunability of the band gap making them interesting for multi-junction device technology. We here compare and highlight trends in the band gap tunability and device performance metrics in reported metal halide perovskite alloys of a wide compositional range from low band gap compounds, such as FA0.75Cs0.25Sn0.5Pb0.5I3 with an absorption onset of 1.2 eV, to high bandgap compounds, such as CsPbBr3 with an absorption onset close to 2.4 eV. In between, metal halide perovskites can seemingly be seamlessly tuned by compositional engineering. However, mixed bromide–iodide compounds with band gaps above 1.7 eV often exhibit photo-induced phase segregation inducing domains with lower band gaps that emit photons of low energy. This effect also reduces the photoluminescence quantum yield and hence the maximum open circuit voltage achievable in devices. This highlight summarizes general trends for metal halide perovskites with respect to their absorption onset. Furthermore recent progress as well as possible roadblocks for the band gap tunability of metal halide perovskites are highlighted as this is of particular importance for the development of multifunction solar cell technology.

Hybrid organo-metal halide perovskites are an exciting new class of solar absorber materials and have exhibited a rapid increase in solar cell efficiencies throughout the past two years to over 17% in both meso-structured and thin-film device architectures. We observe slow transient effects causing hysteresis in the current–voltage characterization of these devices that can lead to an over- or underestimation of the solar cell device efficiency. We find that the current–voltage (IV) measurement scan direction, measurement delay time, and light and voltage bias conditions prior to measurement can all have a significant impact upon the shape of the measured IV light curves and the apparent device efficiency. We observe that hysteresis-free light IV curves can be obtained at both extremely fast and slow voltage scan rates but only in the latter case are quasi-steady-state conditions achieved for a valid power conversion efficiency measurement. Hysteretic effects are also observed in devices utilizing alternative selective contacts but differ in magnitude and time scale, suggesting that the contact interfaces have a big effect on transients in perovskite-absorber devices. The transient processes giving rise to hysteresis are consistent with a polarization response of the perovskite absorber that results in changes in the photocurrent extraction efficiency of the device. The strong dependence of the hysteresis on light and voltage biasing conditions in thin film devices for a period of time prior to the measurement suggests that photo-induced ion migration may additionally play an important role in device hysteresis. Based on these observations, we provide recommendations for correct measurement and reporting of IV curves for perovskite solar cell devices.

Correction for ‘Roadmap and roadblocks for the band gap tunability of metal halide perovskites’ by E. L. Unger et al., J. Mater. Chem. A, 2017, 5, 11401–11409.