SCIENTIFIC HIGHLIGHTS

Printed perovskite LEDs – an innovative technique towards a new standard process of electronics manufacturing
 

Graphical representation of the printing process for the perowskite-LEDs.
© Claudia Rothkirch/HU Berlin

A team of researchers from the Helmholtz-Zentrum Berlin (HZB) and Humboldt-Universität zu Berlin has succeeded for the first time in producing light-emitting diodes (LEDs) from a hybrid perovskite semiconductor material using inkjet printing.This opens the door to broad application of these materials in manufacturing many different kinds of electronic components.The scientists achieved the breakthrough with the help of a trick: "inoculating" (or seeding) the surface with specific crystals.

Microelectronics utilise various functional materials whose properties make them suitable for specific applications. For example, transistors and data storage devices are made of silicon, and most photovoltaic cells used for generating electricity from sunlight are also currently made of this semiconductor material. In contrast, compound semiconductors such as gallium nitride are used to generate light in optoelectronic elements such as light-emitting diodes (LEDs). The manufacturing processes also different for the various classes of materials.

Transcending the materials and methods maze

A look inside the Helmholtz Innovation Lab HySPRINT.
Major work on the printable perovskite-LEDs was carried out here.
 © HZB/Phil Dera

Hybrid perovskite materials promise simplification – by arranging the organic and inorganic components of semiconducting crystal in a specific structure. “They can be used to manufacture all kinds of microelectronic components by modifying their composition“, says Prof. Emil List-Kratochvil, head of a Joint Research Group at HZB and Humboldt-Universität. What's more, processing perovskite crystals is comparatively simple. “They can be produced from a liquid solution, so you can build the desired component one layer at a time directly on the substrate“, the physicist explains.

First solar cells from an inkjet printer, now light-emitting diodes too

Scientists at HZB have already shown in recent years that solar cells can be printed from a solution of semiconductor compounds – and are worldwide leaders in this technology today. Now for the first time, the joint team of HZB and HU Berlin has succeeded in producing functional light-emitting diodes in this manner. The research group used a metal halide perovskite for this purpose. This is a material that promises particularly high efficiency in generating light – but on the other hand is difficult to process. “Until now, it has not been possible to produce these kinds of semiconductor layers with sufficient quality from a liquid solution“, says List-Kratochvil. For example, LEDs could be printed just from organic semiconductors, but these provide only modest luminosity. “The challenge was how to cause the salt-like precursor that we printed onto the substrate to crystallise quickly and evenly by using some sort of an attractant or catalyst“, explains the scientist. The team chose a seed crystal for this purpose: a salt crystal that attaches itself to the substrate and triggers formation of a gridwork for the subsequent perovskite layers.


Significantly better optical and electronic characteristics

In this way, the researchers created printed LEDs that possess far higher luminosity and considerably better electrical properties than could be previously achieved using additive manufacturing processes. But for List-Kratochvil, this success is only an intermediate step on the road to future micro- and optoelectronics that he believes will be based exclusively on hybrid perovskite semiconductors. “The advantages offered by a single universally applicable class of materials and a single cost-effective and simple process for manufacturing any kind of component are striking“, says the scientist. He is therefore planning to eventually manufacture all important electronic components this way in the laboratories of HZB and HU Berlin. List-Kratochvil is Professor of Hybrid Devices at the Humboldt-Universität zu Berlin and head of a Joint Lab founded in 2018 that is operated by HU together with HZB. In addition, a team jointly headed by List-Kratochvil and HZB scientist Dr. Eva Unger is working in the Helmholtz Innovation Lab HySPRINT on the development of coating and printing processes – also known in technical jargon as "additive manufacturing" – for hybrid perovskites. These are crystals possessing a perovskite structure that contain both inorganic and organic components.

Ralf Butscher

Finally, inkjet-printed metal halide perovskite LEDs – utilizing seed crystal templating of salty PEDOT:PSS
Felix Hermerschmidt, Florian Mathies, Vincent R. F. Schröder, Carolin Rehermann, Nicolas Zorn Morales, Eva L. Unger, Emil. J. W. List-Kratochvil.
Mater. Horiz. (2020) Advance Article

 

Modulating the luminance of organic light-emitting diodes via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode
 

Flavie Davidson-Marquis
a) Luminance of an OLED fabricated
with a SAM-modified ITO electrode.
The luminescence doubles
once the DAE is switched from
closed to open.
b) Values for the ratio between
the current densities and
luminescence measured
at 5 V upon multiple irradiation
cycles. The Modulation of the OLED
luminescence is reversible

Organic self-assembled monolayers (SAMs) deposited on inorganic bottom electrodes are commonly used to tune charge carrier injection or blocking in hybrid inorganic/organic optoelectronic devices. Beside the enhancement of device performance, the fabrication of multifunctional devices in which the output can be modulated by multiple external stimuli remains a challenging target. The authors of this CRC 951 research highlight report the functionalization of an indium tin oxide (ITO) electrode with a SAM of a photochromic diarylethene derivative designed for optically control the electronic properties. Following the demonstration of dense SAM formation and its photochromic activity, as a proof-of- principle, an organic light-emitting diode (OLED) embedding the light-responsive SAM-covered electrode is fabricated and characterized. Optically addressing the two-terminal device by irradiation with ultraviolet light (315 nm) doubles the electroluminescence (100% gain), which can be reversed by irradiation with visible light (530 nm). This approach of “dynamic” energy tuning could be successfully exploited in the field of opto-communication technology, for example to fabricate opto-electronic logic circuits.

Modulating the luminance of organic light-emitting diodes via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode

G. Ligorio, G. F. Cotella, A. Bonasera,
N. Zorn Morales, G. Carnicella, B. Kobin,
Q. Wang, N. Koch, S. Hecht,
E. J.W. List-Kratochvil, and F. Cacialli
Nanoscale 12, 5444 (2020)

Review on hybrid integrated quantum photonic circuits

Recent developments in chip-based photonic quantum circuits have radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies and different materials in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits. 

Several key functional elements integrated on single photonic chip

Researchers from the KTH Royal Institute of Technology, Stockholm, Sweden, the University of Muenster, Germany, the National Institute of Standards and Technology, Gaithersburg, USA, and IRIS Adlershof review the progress of hybrid quantum photonics integration. They discuss important design considerations, including optical connectivity and operation conditions, and outline the roadmap for realizing future advanced large-scale hybrid devices, beyond the solid-state platform, which hold great potential for quantum information applications.


Three examples of hybrid integration: (a) Dibenzoterrylene embedded in a rigid matrix of crystalline anthracene as molecule single-photon source on a silicon nitride waveguide [Lombardi, et al. ACS Photon. 5, 126–132 (2018)], (b) Nonlinear phase gate in a hybrid atomic-photonic system [Tiecke, et al., Nature 508, 241–244 (2014)], (c) Hybrid atomic cladding photonic waveguide demonstrating light–matter interaction at room temperature [Stern, et al., Nat. Commun. 4, 1548 (2013)].

Hybrid integrated quantum photonic circuits

A.W. Elshaari, W. Pernice, K. Srinivasan, O. Benson and V. Zwiller
Nat. Photonics (2020)

 

Excited-state charge transfer enabling MoS2/Phthalocyanine photodetectors with extended spectral sensitivity

The combination of inorganic monolayer (ML) transition-metal dichalcogenides (TMDCs) with organic semiconductors holds the promise to further improve opto-electronic device properties with added functionality. The authors of this CRC 951 research highlight investigate a hybrid inorganic/organic system (HIOS) consisting of metal-free phthalocyanine (H2Pc) as thin organic absorber layer and ML MoS2 as TMDC. Via a combination of photoemission (PES), photoluminescence (PL), and photocurrent action spectroscopy they demonstrate, that excited-state charge transfer from the H2Pc layer enhances the photo response of ML MoS2 without loss in sensitivity extended to spectral regions where the TMDC is transparent. This observation is explained by the staggered type II energy-level alignment at the hybrid interface facilitating efficient exciton dissociation and excited-state charge transfer with the holes residing in the H2Pc HOMO and the electrons in the MoS2 conduction band. In hybrid photodetectors, these transferred charges increase the concentration of carriers in MoS2 and with that its photoconductivity. The present demonstration of a highly efficient carrier generation in TMDC/organic hybrid structures paves the way for future nanoscale photodetectors with very wide spectral sensitivity.















(a) Schematic design of the hybrid H2Pc/MoS2 photodetecting device. The H2Pc layer thickness is dH2Pc = 3.0 nm b Photoresponse of the hybrid (blue) and the reference MoS2-only (red) device. The spectra were normalized at the spectral position where H2Pc does not absorb, i.e., between 2.5 and 2.55 eV. The difference between the spectra of the hybrid (Rhyb) and reference (Rref) devices ΔR = Rhyb – Rref (green).

Excited-State Charge Transfer Enabling MoS2/Phthalocyanine Photodetectors with Extended Spectral Sensitivity

N. Mutz, S. Park, T. Schultz, S. Sadofev, S, Dalgleish, L. Reissig, N. Koch, E. J. W. List-Kratochvil, and S. Blumstengel
J. Phys. Chem. C 124, 2837 (2020)

 

Insights into charge transfer at the atomically precise nanocluster/semiconductor interface for in-depth understanding the role of nanocluster in photocatalytic system

A TiO2/cluster composite of type II junction configuration for photocatalytic hydrogen evolution is built by deposition of atomically precise Ag44 nanocluster on TiO2. Besides photosensitizer, the cluster is found to serve as co-catalyst to improve the charge separation efficiency of the system, which is quite different from the well-known plasmonic nanoparticle (NP) enhanced systems. The hydrogen production rate by Ag44-TiO2 is ten times higher than that of the pure TiO2 and five times higher than that of the Ag NP-TiO2.



(a) Schematic illustration of the H2 production by Ag44-TiO2 under simulated sunlight; (b) Catalytic performance of TiO2 (black), Ag NP-TiO2 (yellow) and Ag44- TiO2 (red).

Insights into charge transfer at the atomically precise nanocluster/semiconductor interface for in‐depth understanding the role of nanocluster in photocatalytic system

Y. Wang, X-H. Liu, Q. Wang, M. Quick, A.S. Kovalenko, Q.-Y. Chen, N. Koch, and N. Pinna
Angew. Chem. Int. Ed. 2020

Off-shell gauge invariance

Flavie Davidson-Marquis
Master integrals for reduction of 4-point
functions

Dirk Kreimer (IRIS member), John Gracey (U. Liverpool and DFG Mercator Fellow in Kreimer’s group) and postdoc Henry Kissler could clarify the algebraic and combinatorical foundations of off-shell Slavnov Taylor identities, off-shell gauge invariance that is. The problem remained open in the litera- ture for many years and was now settled by modern algebra and confirmed computation- ally. Quantum chromodynamics served here as a concrete test case. Generalizations to other gauge theories are under study. Figure 1: Off-shell gauge invariance Using Hopf-algebraic structures as well and diagrammatic techniques for deter- mining the Slavnov-Taylor identities for QCD familiar from the study of graph complexes we construct relations for off-shell Green functions. The methods are sufficiently versatile to allow for applications even in the study of diffeomorphism invariance in quantum gravity in the future.

Self-consistency of off-shell Slavnov-Taylor identities in QCD
J. A. Gracey, H. Kißler, and D. Kreimer
Phys. Rev. D 100 (2019) 085001



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