In her research Khan studied titanium dioxide (TiO2), a versatile semiconductor material, that holds immense promise in the realm of solar energy and is a key component in numerous photocatalytic and photovoltaic applications. However, unlocking its full potential requires mastering its structural and optoelectronic properties.
“That is where my research steps in. The team I work in has employed atomic layer deposition (ALD) to synthesize TiO2 thin films with controlled parameters, meticulously optimising their optoelectronic properties for enhanced performance in photonic devices,” Khan says.
Her study centres around utilising femtosecond transient absorption spectroscopy, which allows monitoring the dynamics of photogenerated charge carriers within these TiO2 thin films upon excitation with a suitable wavelength.
Khan noticed that the excitation of the TiO2 films not only changes the absorption of the sample but also its reflection, which made it impossible to interpret the transient signal without taking the reflection into account. In many previous studies, reflection had not been considered at all. Therefore, she examined the films in both transient transmittance and transient reflectance modes to unlock crucial insights into the photoinduced optoelectronic changes in the films. Moreover, considering the changes in the refractive index provides an opportunity to study the diffusion of carriers across the films as well.
The culmination of the research team’s efforts has revealed an exciting discovery: the careful control of ALD growth temperature, coupled with a specific heat-treatment regime leads to the production of anatase TiO2 films with significantly extended carrier lifetimes. This matters as the enhanced carrier lifetime translates into the improved functionality of photonic devices.
“However, the significance of the work does not stop there. These optimized TiO2 films exhibit remarkable potential as corrosion protection layers over light absorbing materials such as silicon and boast favourable properties for a seamless interfacial charge transfer in TiO2–Si heterojunctions. This breakthrough is not just theoretical; it is practical!” Khan says.
By optimizing the transport of carriers from silicon through the TiO2 layer to catalytic centres in the TiO2–Si heterojunctions-based photovoltaic and photoelectrochemical devices, the efficiency and overall energy conversion will be significantly enhanced.
“I am delighted to have had the opportunity to conduct research on the optimization of the sustainable energy materials which is a profoundly crucial and relevant topic right now,” she adds.
Ramsha Khan is originally from Pakistan. She has been working as a doctoral researcher in the Photonic Compounds and Nanomaterials team at Tampere University since 2019.
Public defence on Friday 19 January
The doctoral dissertation of M.Sc. Ramsha Khan in the field of chemistry titled Charge Carrier Dynamics in TiO2 Thin Films for Photonic Applications will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12.00 on Friday 19 January 2024 on the Hervanta campus in auditorium Pieni Sali 1 of the Festia building.
The Opponent will be Senior lecturer Dr. Tatu Kumpulainen from the University of Jyväskylä. The Custos will be Professor Nikolai Tkachenko from the Faculty of Engineering and Natural Sciences.
The doctoral dissertation is available online.
The public defence can be followed via a remote connection.
Photo: Ambreen Khan