The role of carrier and spin dynamics in novel organic optoelectronic devices

Autor: Gillan, Lara
Jazyk: angličtina
Rok vydání: 2022
Předmět:
DOI: 10.26190/unsworks/24402
Popis: For decades the solar technology industries have been dominated by silicon-based devices due to their relatively high efficiencies and long-term operational and environmental stability. While silicon remains a reliable material for use in solar technologies, the potential for substantial reduction in cost per watt has become limited. The maturity of silicon has seen efficiencies plateau - as devices approach the thermodynamic limit - while fabrication costs remain relatively high compared to other solution processable techniques, creating an opening for newer solar harvesting materials and devices to be developed, potentially driving the cost per watt down. Identifying new solar harvesting materials requires a balance between power generation efficiency, cost of production and maintenance, and stability. Understanding the underlying electronic processes which enable their operation, such as spin and charge dynamics, is imperative to improving solar power conversion efficiencies. In this thesis, the fundamental electronic processes which define and control the performance of organic and perovskite materials for use in solar cells and light-emitting diodes are investigated using a variety of microwave and magnetic-field-based techniques. The spin-dependent operation of organic photovoltaics is probed through transient electron paramagnetic resonance (trEPR) and magneto-photocurrent measurements. These results highlight the critical role of the charge-transfer state in free carrier generation. The effective energetic alignment of the HOMO and LUMO in P3HT:[70]PCBM blends efficiently dissociates excited species to free carriers without parasitic back electron transfer. Investigation of the carrier dynamics following photoexcitation in perovskite films by time-resolved microwave conductivity (TRMC) measurements demonstrates additive-based morphology improvement of the recombination processes, with improved diffusion lengths for all measured wavelengths and intensities. Finally, 2D perovskites and hybrid organic/perovskite architectures are explored for their capacity for light emission. Magneto-photoluminescence measurements of (PEA)2PbI4 reveal spin mixing between excitonic states at low temperatures. Upconversion is demonstrated in a rubrene/perovskite bilayer structure, revealing anomalous temperature-dependent upconverted emission in sensitiser-free DBP and rubrene (DBP) films. The insights gained in the thesis will help inform material choice and design of emerging optoelectronic devices, improving power conversion efficiencies, and light-emitting diode stability.
Databáze: OpenAIRE
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