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Guest talks

Dr. Wenxin Mao (Guest talk, Monash University)

i-MEET, seminar room 3.71
Martensstraße 7, 91058 Erlangen

07.10.2019, 11:00

Organo-lead halide perovskites (OHPs) have recently emerged as a new class of exceptional optoelectronic materials. However, despite the thorough studies into lead halide perovskites during over past 10 years, there are still many unknowns concerning both the device performance and the stability.
The first part of this presentation introduces the fabrication of a single-crystalline perovskite based electric-optical modulator device through a novel solution-processed perovskite crystal growth method. The as-synthesized MAPbBr3 microplatelets were tailored into a waveguide-based photonic device, of which an efficient active electro-optical modulator (AEOM) consisting of a MAPbBr3 non-linear arc waveguide was demonstrated, exhibiting a 98.4% PL intensity modulation with an external voltage of 45 V. This novel synthetic approach as well as the demonstration of effective waveguiding will pave the way for developing a wide range of photonic devices based on organo-lead halide perovskites.
The second part of this presentation explores the much-debated mechanism of light induced phase segregation in mixed halide perovskite single crystals. Herein, a method for growing large (30×30×1 μm) monocrystalline MAPb(BrxI1-x)3 single crystals is presented. The direct visualisation of the growth of nanocluster-like I-rich domains throughout the entire crystal revealed grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time-resolved spectroscopy provided new insight into the nature of phase segregated domains and the collective impact on optoelectronic properties.

Dr. Fabian Panzer (Guest talk, University of Bayreuth)

30.10.2019, 11:00

Helmholtz-Institut Erlangen-Nürnberg (HI ERN)
Fürther Str. 248, 90429 Nürnberg

Understanding and controlling perovskite film formation – optical in situ characterizations during solution processing and a solvent free route for film processing based on pressure treatment of perovskite powders

Optoelectronic devices based on hybrid perovskites have undergone a remarkable development in recent years mainly due to enormous efforts in optimizing their film properties. However, the relatively complex film formation dynamics as they occur, e.g. during solution processing, has not yet been addressed and understood in detail. In the first part of my talk I discuss measurements of absorption and photoluminescence (PL) during a solution based two-step synthesis of the model hybrid perovskite CH3NH3PbI3 in situ while spin coating. We observe changes in both, absorption and PL during the spin-coating process which allows us to identify different time regions with specific spectral changes. Our results suggest that prior to film formation, a variety of intermediate states exist in the electronic structure to which the transition rates can be altered with temperature.

In the second part of my talk I will present an alternative, entirely dry processing approach, decoupling perovskite crystallization and film formation, by using readily prepared perovskite powders and produce films by appropriate mechanical pressure treatment. We show how a mechanochemical synthesis by ball milling allows to produce a wide range of phase pure and highly stable perovskite powders with a high flexibility in processing and we address the impact of milling parameters on the powder properties. Using these powders, we demonstrate how the used pressure and the powder microstructure, i.e. particle size and stoichiometry affect the mechanical stability, compactness and surface roughness of the pressed layers. We further address how specific temperature treatment during the pressing step can improve the properties of the pressed layer, and show their capability to be used in perovskite based optoelectronic devices.

Short Biography:

Dr. Fabian Panzer (born in Marktredwitz, Germany, 1988) is a Junior Researcher (Habilitand) at the Chair for Soft Matter Optoelectronics at the University of Bayreuth. He studied Physics at the University of Bayreuth where he obtained his PhD in 2016 with honors. A major interest of his work is to understand how changes in the conformation or structure of organic or hybrid semiconductors affect their optical properties. With these findings he addresses technical and application-oriented questions of these semiconductor materials, with a focus on their film formation process, to advance their successful processing in an industrial context.

Towards Single-Crystalline Perovskite Devices