Control of excitation recombination and transfer with tailored material design

• Applicant: Professor Dr. Felix Deschler
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387651688

There is a constant search for new semiconducting materials with tailored properties for optimised, more efficient applications. Functional materials are omnipresent in technology, and specifically semiconductors have promoted high-tech electronics and sustainable energy generation. However, guided exploration of the immense materials space has been limited, since a fundamental paradigm on how structure and composition control electronic and optical properties of high-quality semiconductors is missing.I will address and overcome this limitation by a combined spectroscopic and structural investigation on how the dimensionality of excitations effects their photo-physical properties, with particular focus on radiative recombination and excitation transfer at interfaces. Here, materials are required, in which the photo-physical properties of excited states can be tailored by facile, controlled variations of material parameters. This is now possible in the recent material class of hybrid metal-halide perovskites - so far mostly investigated for their use in photovoltaic applications - which provides an exciting scientific opportunity. I propose a broader fundamental scientific scope for hybrid perovskites, which aims to take the field beyond its current device-optimisation driven research. Changes in crystal structure, dimensionality and composition in these solution-processed materials, give now unprecedented control over excited states and band structure. Further, efficient excited state conversion requires clarification of the energy and charge transfer processes between materials, which exhibit excited states with distinct electronic properties. Multilayer hetero-junctions with perovskite monolayers will provide unique van der Waals structures, likely with novel physical features. These will give the opportunity to study transfer processes at single-atom interfaces between nanosheets without the interference from bulk effects and disorder.The results from my research programme will generate impact in two directions: (1) Insights on fundamental connections between material structure and excited state properties answer central physical questions on the material control of electronic states. Feedback of these criteria to informatics-based approaches will change the current perspective on material exploration. (2) Identification of the criteria for high-quality semiconductors will lead to the discovery of unexpected, novel materials for optoelectronic applications. The tailored development of optical electronic properties will produce solar cells and light-emitting diodes with optimised efficiency. To achieve this, I bring proven expertise in the study of the photo-physical and electronic properties of novel semiconductors, with a wide range of excited state properties, combined with competence in advanced spectroscopic and structural investigation techniques.

• DFG Programme: Independent Junior Research Groups
• Major Instrumentation: High pulse energy, high repetition rate amplifier laser system ; SNOM-AFM ; iCCD camera
• Instrumentation Group: 5091 Rasterkraft-Mikroskope ; 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek) ; 5700 Festkörper-Laser