Photoluminescence and transient absorption spectroscopy techniques applied to perovskite semiconductors.

General context:

Over the past few years, a new class of promising materials, Organic-Inorganic Perovskites, has attracted global scientific interest, because of impressive performance in new generation solar cells. These materials are also of high importance for modern technology, as they serve as active layers in light emiting devices (LEDs). Therefore, the understanding of the photophysical properties of these materials, as well as their interaction with other materials when implemented in complete devices, is very crucial. Ultrafast spectroscopy is a valuable tool for the investigation of the intrinsic photophysical properties of such semiconductors and their interaction with other materials acting as electron/hole acceptors or donors.

Specific objective: MASTER THESIS

The current project has two parts. The first focuses more technically on understanding time-resolved spectroscopic techniques that allow to observe the evolution of different processes on the nanosecond timescale. You will have the opportunity to familiarize with the existing set-ups and will construct a set-up for transient absorption spectroscopy. In the second part, you will use this setup to study the photophysical properties of modern semiconducting materials, namely Perovskites, for applications in LEDs and solar cells.

You will learn:

Functioning of new generation solar cells and LEDs
Laser Spectroscopy techniques in the nanosecond timescale
Intrinsic semiconductor properties
Ultrafast processes taking place in perovskites and at their interface with other materials

A word about the group:

We are a small group of 10 people with either a Chemistry, a Physics or a Materials background. Our research evolves around the central question of what happens on the ultrashort time scale and ultra small length scale in both organic and hybrid semiconductors with applications in new generation solar cells, organic transistors and (biological) sensors. We propose a mechanistic, physical-chemistry approach, but with multidisciplinary scope at the interface of chemistry, physics, engineering and materials science. Experimentally, we use a complementary palette of techniques combining time-resolved spectroscopy, pulsed photocurrent methods, terahertz experiments, Stark-effect spectroscopy and device testing. In the case of your master thesis, you will be supervised by a PhD student. If you have questions, please don’t hesitate to contact us and we’ll be happy to discuss this project with you.

Contacts:

Prof. Natalie Banerji, office 525, natalie.banerji@dcb.unibe.ch

Nikos Droseros, office 524, nikolaos.droseros@dcb.unibe.ch

Studying PEDOT:PSS, from scratch to THz spectroscopy.

General context: OSIRIS PROJECT

Organic biosensing and bioelectronics is a young, dynamic and exciting field, uniting researchers from highly diverse backgrounds – life sciences, synthesis, physical chemistry, solid-state physics, materials science and device engineering. One prominent example in bioelectronics are OECTs (organic electrochemical transistors). Such devices can be integrated with living cells, tissues and organs to monitor cellular activity. However, an in-depths understanding of the underlying fundamental processes and working principles of OECTs is still lacking. The vision of the ERC-funded OSIRIS project (organic semiconductors interfaced with biological environments) is to pioneer a new research direction by bringing sophisticated spectroscopic studies into this emerging field.

Specific objective: MASTER THESIS

The aim of this Master project will be the preparation and characterization of PEDOT:PSS polymers films which are the key component of OECT devices. Due to its excellent chemical stability, good charge transport properties and low cytotoxicity, PEDOT:PSS is one of the most used polymers for bioelectronic applications. Yet, a complete characterization of its optical and terahertz spectroscopic properties has not been reported in the literature. As a first step, your objective will be to prepare a panel of PEDOT:PSS films with different thicknesses and morphologies. In a second step, you will characterize them in state of the art ultrafast spectroscopy laboratories. You will be introduced to different spectroscopic setups with a particular emphasis on terahertz techniques. Depending on your interests, you may also be involved in the design and conception of a new kind of spectroscopic setup, or in the design of devices interfacing solid polymer films with liquid electrolytes. The results of this work will likely lead to a publication, in which you will be involved.

You will learn:

How to design and plan a research project.

How to prepare doped polymer films using different techniques like spin-coating, drop casting.

How to manipulate spectroscopic setups and analyze the results of your measurements.

How to efficiently formulate and report your research.

A word about the group:

If you have questions, please don’t hesitate to contact us and we’ll be happy to discuss this project with you.

Contacts:

Prof. Natalie Banerji, office 525, natalie.banerji@dcb.unibe.ch

Gonzague Rebetez, PhD students, office 530, gonzague.rebetez@dcb.unibe.ch

Dr. Julien Réhault, office 524, julien.rehault@dcb.unibe.ch