Compact Layers of Hybrid Halide Perovskites Fabricated via the Aerosol Deposition Process : Uncoupling Material Synthesis and Layer Formation

We present the successful fabrication of CH3NH3PbI3 perovskite layers by the aerosol deposition method (ADM). The layers show high structural purity and compactness, thus making them suitable for application in perovskite-based optoelectronic devices. By using the aerosol deposition method we are able to decouple material synthesis from layer processing. Our results therefore allow for enhanced and easy control over the fabrication of perovskite-based devices, further paving the way for their commercialization

Structural diversity in layered hybrid perovskites, A2PbBr4 or AA′PbBr4, templated by small disc-shaped amines

Y.-Y.G. and T.L. acknowledge the University of St Andrews and China Scholarship Council for funding of studentships (201603780005) and (201606280032), respectively. J.A.M. and P.L. acknowledge financial support from the Leverhulme trust (RPG-2018-065). S.B., K.S. and F.P. acknowledge financial support from the German National Science Foundation via the Projects 423895689, KO 3973/2-1 and PA 3373/3-1 and further acknowledge support by the Bavarian State Ministry of Science, Research, and the Arts for the Collaborative Research Network ‘‘Solar Technologies go Hybrid’’.We present three new hybrid layered lead(II) bromide perovskites of generic composition A2PbBr4 or AA′PbBr4, which exhibit three distinct structure types. [TzH]2PbBr4, ([TzH+]= 1,2,4-triazolium), adopts a (001)-oriented layer structure, [AaH]2PbBr4, ([AaH+] =acetamidinium), adopts a (110)-oriented type, whereas [ImH][TzH]PbBr4, ([ImH+] =imidazolium),adopts a rare (110)-oriented structure with enhanced corrugation (i.e. ‘3 ×3’ type). The crystal structures of each are discussed in terms of the differing natureof the templating molecular species. Photoluminescent spectra for each are reported and the behaviours discussed in relation to the different structure of each composition.PostprintPeer reviewe

A unified picture of aggregate formation in a model polymer semiconductor during solution processing

One grand challenge for printed organic electronics is the development of a knowledge platform that describes how polymer semiconductors assemble from solution, which requires a unified picture of the complex interplay of polymer solubility, mass transport, nucleation and, e.g., vitrification. One crucial aspect, thereby, is aggregate formation, i.e., the development of electronic coupling between adjacent chain segments. Here, it is shown that the critical aggregation temperatures in solution (no solvent evaporation allowed) and during film formation (solvent evaporation occurring) are excellent pointers to i) establish reliable criteria for polymer assembly into desired aggregates, and ii) advance mechanistic understanding of the overall polymer assembly. Indeed, important insights are provided on why aggregation occurs via a 1- or 2-step process depending on polymer solubility, deposition temperature and solvent evaporation rate; and the selection of deposition temperatures for specific scenarios (e.g., good vs bad solvent) is demystified. Collectively, it is demonstrated that relatively straightforward, concurrent in situ time-resolved absorbance and photoluminescence spectroscopies to monitor aggregate formation lead to highly useful and broadly applicable criteria for processing functional plastics. In turn, improved control over their properties and device performance can be obtained toward manufacturing sensors, energy-harvesting devices and, e.g., bioelectronics systems at high yield

Understanding Differences in the Crystallization Kinetics between One-Step Slot-Die Coating and Spin Coating of MAPbI₃ Using Multimodal In Situ Optical Spectroscopy

To develop a detailed understanding about halide perovskite processing from solution, the crystallization processes are investigated during spin coating and slot-die coating of MAPbI3 at different evaporation rates by simultaneous in situ photoluminescence, light scattering, and absorption measurements. Based on the time evolution of the optical parameters it is found that for both processing methods initially solvent-complex-structures form, followed by perovskite crystallization. The latter proceeds in two stages for spin coating, while for slot-die coating only one perovskite crystallization phase occurs. For both processing methods, it is found that with increasing evaporation rates, the crystallization kinetics of the solvent-complex structure and the perovskite crystallization remain constant on a relative time scale, whereas the duration of the second perovskite crystallization in spin coating increases. This second perovskite crystallization appears restricted due to differences in solvent-complex phase morphologies from which the perovskite forms. The work emphasizes the importance of the exact precursor state properties on the perovskite formation. It further demonstrates that detailed analyses of multimodal optical in situ spectroscopy allows gaining a fundamental understanding of the crystallization processes that take place during solution processing of halide perovskites, independent from the specific processing method