Jana Wulf was born on November 17th 1990 in Rotenburg (Wümme).
She received her bachelor’s and master’s degree in nanoscience at the Julius-Maximilians-Universität in Wuerzburg. Due to her interest in renewable energies she chose the research field of organic solar cells for her master thesis. During her studies Jana Wulf spent two semesters abroad studying physics at the University of New Mexico in Albuquerque, USA and three months as a research intern in the field of MEMS/NEMS at the indian institute of science (IISc) in Bangalore, India. Moreover, she worked as an intern, working student and employee in the field of research and development at the company va-Q-tec AG in Wuerzburg, a company developing energy efficient and environmental friendly vacuum isolation panels. In 2018 Jana Wulf started researching on the topic of epitaxial lift-off of III-V cells at the Fraunhofer institute of solar energy systems (ISE) in Freiburg.
Short description of the doctoral thesis:
The goal of the dissertation project is the development and optimization of an industrial scalable epitaxial lift-off process for high efficiency III-V on silicon solar cells. The current record efficiency for silicon solar cell (Kaneka 2017: 26,7%) is very close to the practical limit of around 27%. Higher efficiencies can be reached with multi-junction solar cells.
At the Fraunhofer institute for solar energy systems an III-V on Si solar cell with an efficiency of 33.3% was demonstrated in 2017. The III-V top cells grown on a GaAs substrate which has to be chemically etched away after successful bonding the top cells to the silicon bottom cell, hence the substrate is lost. Reusing the expensive GaAs substrate for another growth process can be realised by developing the epitaxial lift-off process. The idea is to separate the very thin III-V cell from the substrate by using the highly selective etching of an Aluminum Arsenide (AlAs) sacrificial layer with hydrofluoric acid while keeping the substrate intact.
In the first part of the thesis the etching behaviour of an AlAs sacrificial layer will be analyzed in detail. Through experiments and dynamic microfluidic modelling a precise understanding of the sacrificial layer etching will be developed. The next step is to apply three different approaches of the epitaxial lift-off process. After evaluating the most promising route, this approach will be optimized and implemented for the realization of III-V on silicon solar cells. Finally, the reuse of the GaAs substrate will be demonstrated.