Controlling luminescence properties of 2D perovskites by structural design
Date of Issue2018-02-02
Interdisciplinary Graduate School
Energetics Research Institute
Metal halide perovskites are rapidly emerging for their light emitting properties, making perovskite-based light-emitting diodes, transistors, lasers and scintillators the new frontier of solution-processable optoelectronic devices. In this regard, two-dimensional perovskites are extremely appealing due to their increased synthetic versatility, which allows the incorporation of a wider range of organic and metallic cations for the fine-tuning of their optoelectronic properties. Hybrid functional materials can be synthetized by including optoelectronically active cations within the perovskite framework and provide new emissive properties to the resulting hybrid system. On the other hand, the templating properties of organic cations can be exploited to control the structural arrangement of the inorganic motif and the interplay between excitonic and polaronic properties to induce narrow- to ultrabroad-band luminescence. The rational synthetic design to achieve optical properties on demand is conditional to the understanding of the self-assembling behaviour and photophysical processes underlying the emissive properties of these materials, which are still mostly unexplored. In this thesis project, crystal engineering principles are applied for the design and synthesis of perovskites with desired luminescence properties. Such model materials are studied by a combination of steady state and time resolved spectroscopic measurements and ab initio simulations to reveal the interplay between structure and optical properties in both lead-free and lead-based systems. Firstly, we show that active functional cations can be used in combination to copper perovskites to overcome their limitations in terms of emission tunability and stability. Furthermore, we employ the organic cations as templating elements to induce specific structural arrangements and distortions of the inorganic framework in lead-based perovskites and to selectively tailor their luminescence bandwidth and energy by structural design. We argue that the formation of small polaronic species localized at specific sites of the inorganic lattice are responsible for the photoluminescence broadening in 2D perovskites, ultimately leading to white light emission. Our results highlight the importance of perovskite’s structural engineering to achieve a rational synthetic design of the material, and point to a wider consideration of the role of polarons and charge self-trapping in hybrid perovskites. The ability to selectively control the optoelectronic properties in these low-dimensional systems will provide distinctive advantages for their application in solid-state lighting and scintillators.