Self-Trapped Excitons in Low-Dimensional Perovskites - Do They Exst?
Simon Kahmann a, Eelco K. Tekelenburg a, Herman Duim a, Maria A. Loi a
a University of Groningen, The Netherlands, Nijenborgh, 4, Groningen, Netherlands
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Oral, Simon Kahmann, presentation 057
Publication date: 25th November 2019

We resolve a controversy surrounding the luminescence properties of low-dimensional halide perovskites and clarify that an often observed broad luminescence arises from defect states instead of commonly invoked self-trapped excitons.

Low dimensional halide perovskite are a class of semiconductors with intriguing opto-electronic properties showing already impressive performance metrics in devices. Whilst initial research in this field was predominantly driven by photovoltaic research and more recent efforts focused on the narrow emission linewidth in many of these compounds, the latest hotly examined observation is the presence of broad emission bands. This broad emission has the potential for direct white light generation and significant research is currently conducted to find and optimise compounds for this purpose. Crucially, these efforts commonly base on the assumption that the origin of this luminescence is a so-called self-trapped exciton. Whilst this concept is elegant and theoretical calculations have offered some support, experimental evidence for this interpretation is so far scarce.

We therefore studied single-crystals of two-dimensional lead iodide perovskites through a variety of spectroscopic techniques and prove that the broad emission is in fact due to defect states in the bulk of the material. We study two different compounds to underline the universality of our findings and meticulously exclude all other origins of broad emission bands that have hitherto been proposed.

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