Charge Carrier Localisation in Metal Halide Perovskites for Optoelectronic Applications

This dissertation is concerned with the charge carrier dynamics in semiconductors based on metal-halide perovskites. These materials have shown remarkable performance in optoelectronic applications like solar cells or light-emitting devices. They are solution-processable at low temperature using inexpensive earth-abundant reagents, have low Urbach energies, high carrier mobilities and long diffusion lengths, while their bandgap can be tuned across the visible and near-infrared spectrum through the chemical composition. In this thesis, two different perovskite-based systems are studied with respect to their carrier dynamics and related photoluminescence yields as a probe for their performance in devices. The first study compares a variety of perovskite thin films containing mixed cations (cesium, methylammonium, formamidinium) and mixed halides (bromide, iodide). I find that the disordered energetic landscape arising from domains that are bromide- or iodide-rich allows charge carriers to accumulate in low-bandgap regions. Recombination of charges at these sites follows quasi-first-order kinetics and the locally high carrier density allows bimolecular radiative recombination to outcompete trap-mediated loss channels. Thus, the photoluminescence yields in mixed-halide compositions remain high even at low excitation densities. This unearths a new route towards highly efficient light-emitting devices or solar cells through micro-structuring of the energy landscape in these materials. The second study investigates the consequences of manganese-doping for the carrier dynamics of cesium lead halide nanocrystals. Photoluminescence quantum yields are shown to double upon doping. This is found to be not only a consequence of reduced non-radiative losses, but of an increased intrinsic radiative excitonic recombination rate as well. The origin of this stronger emission lies in a carrier localisation effect induced by the manganese dopants which locally break the periodicity of the host crystal lattice. This leads to an increased overlap of electron and hole wave functions and thus favours radiative recombination. The mechanism provides a new strategy of transition-metal doping for highly efficient light-emitting devices.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Feldmann, Sascha

Advisor dc:contributor.advisor

• Friend, Richard Henry

• spectroscopy
• halide perovskites
• optoelectronics
• solar cells
• light-emitting diodes
• semiconductors

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/6e003024-0a3a-4fc7-ad3b-44bff45d457c/download
• https://creativecommons.org/licenses/by-nc-sa/4.0/

Language dc:language

eng

Author Identifier

0000-0002-6583-5354

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/317717