3 positions for PhD students or postdocs are available for laser spectroscopy on dynamics
of excitons and charges in organic materials and quantum dots for solar cells.
Location: Laurens Siebbeles group at TU Delft, The Netherlands, www.dct.tudelft.nl/om
Research topic
You will study the dynamics of excitons and charge carriers with femtosecond and
nanosecond pump-probe laser techniques, including microwave and terahertz conductivity
measurements. In addition high-energy electron pulses can be used to specifically
generate charges. Materials of interest include quantum dots, phthalocyanine dye
molecules and conjugated polymers. A brief description of the projects is given below.
Further information and applications
Prof. Laurens D.A.Siebbeles
e-mail: [log in to unmask]
Please send your CV, a letter of motivation (1/2 A4) and letter(s) of recommendation.
Projects
1. Laser Spectroscopy on Multiple Excitons in Quantum Dots for Solar Cells
Semiconductor quantum dots are of great interest for application in solar cells that are
both cheap and highly efficient. The high potential efficiency is due to the fact that a
single photon can excite two or more electrons in a quantum dot. This process of so-
called carrier multiplication has been established very recently. The next challenge to be
addressed in this project is to extract the multiple charges from the quantum dots.
Your studies focus on quantum dots in blend films with metaloxides and organic materials
as electron and hole acceptors. Effects of the composition and size of the quantum dot
and blend composition on the efficiency of free charge generation will be studied with
time-resolved laser spectroscopy. Exciton decay, charge formation and decay via
recombination or trapping will be monitored on timescales ranging from tens of
femtoseconds to milliseconds. Your research will provide knowledge about the optimal
material for highly efficient solar cells in which a single photon creates two or more
electron-hole pairs.
2. Spectroscopy on Excitons and Charges in Molecular Materials for Solar Cells
Currently there is great interest in the use of organic molecules as the active component
in cheap and flexible solar cells. The project will be carried out in collaboration with the
BASF company. Particular interest exists in phthalocyanine molecules, due to large
absorption of the infrared part of the solar spectrum and prospects for achieving a higher
cell voltage. To realize solar cells on basis of these molecules fundamental understanding
of the steps from light absorption to generation of free charges that can contribute to the
photocurrent is essential.
The aim of the project is to provide insights into the influence of the chemical structure of
the molecules and the thin film nanostructure on charge and exciton mobility and lifetime.
Using time-resolved spectroscopic methods you will study to which extent exciton
diffusion and exciton dissociation into mobile charges can be optimized. Particular
attention will be paid to charge generation in composite systems of phthalocyanines and
C60 as electron acceptor. The mechanism of motion of excitons and charges in the
materials will be characterized.
3. Laser Spectroscopy on Conjugated Polymers for Organic Electronics
Currently there is great interest in the use of conjugated polymers as the active
component in cheap and flexible electronics, including transistors, solar cells and LEDs.
The project will be carried out in collaboration with Merck Chemicals Limited in the UK.
Particular interest exists in new thiophene based polymers with improved properties for
application in (opto)electronic devices.
The aim of the project is to provide insights into the influence of the chemical structure of
the polymers and the thin film nanostructure on charge and exciton mobility and lifetime.
You will study the dynamics of excitons and charge carriers with time-resolved laser
spectroscopy and high-energy electron pulses. You will study to which extent
photoexcitation of the polymer leads to generation of excitons and free charges. The
relation between material structure and charge mobility will be investigated. Exciton
diffusion and dissociation into mobile charges will be studied for blends of the polymers
with electron acceptors. The studies will provide information about the mechanism of
motion of excitons and charges.
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