Research Melissa Van Landeghem

Abstract

The weak spin-orbit interaction inherent to organic semiconductors makes them ideal candidates for spintronics applications. While typical spin lifetimes easily surpass those of their inorganic counterparts by several orders of magnitude, the main limitation in organic spin transporters is the spin diffusion length, often not exceeding 50 nm. It has now been established that spins in organic materials can be transported either by mobile charges or via spin exchange between localized polarons. The latter mechanism opens up an interesting new avenue toward longer spin diffusion lengths by increasing the intrinsic spin density of the materials. In 2019, record spin diffusion lengths of 1 um have been reported for the first time in a highly-doped polymer. In this project, I propose to investigate spin transport in paramagnetic polymers, a recently-discovered class of ultra-low-bandgap semiconductors exhibiting a triplet ground state and hence a large intrinsic spin density. Spin transport experiments will be performed in state-of-the-art spintronic devices based on spin pumping injection. In addition, the combination of electron paramagnetic resonance methods and supporting quantum-chemical computations will provide detailed information on spin delocalization and spin-spin-interactions. By expanding my study to a series of these polymers, structure-property relations can be elucidated and used to establish the fundamentals of spin transport in these innovative materials.

Researcher(s)

• Promoter: Van Doorslaer Sabine
• Co-promoter: Cambré Sofie
• Fellow: Van Landeghem Melissa

Research team(s)

• Biophysics and Biomedical Physics
• Theory and Spectroscopy of Molecules and Materials (TSM²)

Project type(s)

• Research Project

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 21% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also appear due to degradation, thereby reducing the useful lifetime of the solar cells. The main goal of my project is the identification and characterization of the defects that set a limitation to the solar cell performance. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects and of their surroundings. Knowledge of the electronic structure and creation processes of the defects will allow to design better perovskite materials for these solar cells and to optimize the device fabrication process.

Researcher(s)

• Promoter: Goovaerts Etienne
• Co-promoter: Van Doorslaer Sabine
• Fellow: Van Landeghem Melissa

Research team(s)

• Nanostructured and organic optical and electronic materials (NANOrOPT)

Project type(s)

• Research Project

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 21% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also appear due to degradation, thereby reducing the useful lifetime of the solar cells. The main goal of my project is the identification and characterization of the defects that set a limitation to the solar cell performance. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects and of their surroundings. Knowledge of the electronic structure and creation processes of the defects will allow to design better perovskite materials for these solar cells and to optimize the device fabrication process.

Researcher(s)

• Promoter: Goovaerts Etienne
• Co-promoter: Van Doorslaer Sabine
• Fellow: Van Landeghem Melissa

Research team(s)

• Nanostructured and organic optical and electronic materials (NANOrOPT)

Project type(s)

• Research Project

Abstract

Organometal trihalide perovskite solar cells have in the few years since their first introduction (in 2009) demonstrated very high power conversion efficiencies, up to 18% with potential for further increase. It is announced to become a game changer in the field of thin film photovoltaics, but this will critically depend on avoiding defect formation in the perovskite layer as well as at the interfaces with adjacent layers. The defects act as trapping centers for negative and positive charge carriers and as such impede the carriers to contribute to the photocurrent. The defects may result from the material synthesis and device fabrication methods, but they can also increasingly appear due to degradation, thus reducing the useful lifetime of the solar cells. The main goal of my project is the identification of the defects that either set an initial limitation to the solar cell performance or else cause degradation of the solar cell during operation. To learn about the geometric and electronic structure of these defects I will apply multi-frequency electron paramagnetic resonance (EPR) techniques which are able to reveal the nature of the defects. Knowledge of the electronic structure and creation processes of the defects will allow designing better perovskite materials for these solar cells and to optimize the device fabrication.

Researcher(s)

• Promoter: Goovaerts Etienne
• Co-promoter: Van Doorslaer Sabine
• Fellow: Van Landeghem Melissa

Research team(s)

• Nanostructured and organic optical and electronic materials (NANOrOPT)

Project type(s)

• Research Project