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Michael Rauer was born in Herbolzheim on April 10, 1984.
Michael Rauer studied Physics at the Albert-Ludwig-University Freiburg and graduated in September 2009. During his studies he worked as student assistant at the University of Freiburg and at the Fraunhofer Institute for Solar Energy Systems (ISE), which offered him insight into the development of photovoltaic systems. This led him to conduct his diploma thesis, entitled "Evaluation and Optimisation of PECVD Layers for the Surface Passivation of n-type Silicon Solar Cells", at ISE under the supervision of Prof. Eicke Weber. His PhD project expands and furthers the work begun with this diploma thesis.
"Evaluation of New Technologies for the Realisation of High Efficiency n-type Silicon Solar Cells"
Today's solar cell fabrication is mainly focused on cells produced of boron-doped p-type crystalline silicon material due to historical reasons. Phosphorous-doped n type silicon is only sparsely used, even though it provides superior electrical properties, which makes this material well-suited for the fabrication of high-efficiency silicon solar cells.
However, switching from p-type to n-type silicon presents technological challenges for solar cell manufacturing, particularly for the fabrication of the highly-doped p+ emitter, which accounts for the separation of photo-generated charge carriers. A cost-effective and industrially feasible approach is based on screen-printing aluminium paste onto the back side of the wafer and forming the highly Al-doped p+ region in a subsequent high temperature alloying step. Promising solar cell efficiencies exceeding 20% have been reported recently for this solar cell structure, however, thereby benefiting from various time-consuming and complex fabrication steps.
Therefore, this PhD project aims at further developing and improving n-type Si solar cells with screen-printed Al-alloyed rear emitters by using industrially feasible fabrication techniques. In addition to the implementation of innovative technologies, a pronounced physical understanding of the Al emitter formation shall be developed within the scope of this PhD project.
By theoretically modelling the Al-Si alloying process, predictions of the emitter homogeneity and the emitter surface properties are to be enabled. At the same time, the modelling allows the incorporation of impurity atoms into the Al-p+ emitter to be investigated in order to define purity standards.
Technologically, the implementation of the emitter surface passivation, i.e. the deactivation of defect centres at the emitter surface, shall be included into the solar cell concept with the use of industrially relevant techniques. As has been demonstrated for the "time-consuming solar cell concept", the emitter passivation can lead to a considerable improvement of the cell efficiency. First promising approaches are already under investigation at Fraunhofer ISE.
Another issue, which is especially important for solar cells with rear emitter, deals with the formation of selective phosphorous-doped front-surface-fields. Since the front side of such a selectively-doped n type Si solar cell is a very complex system, comprising many parameters, multidimensional simulations will be performed to support optimisation.
The key goal of this PhD project is the concluding combination of the optimised industrial fabrication techniques with the knowledge of the emitter formation to manufacture high efficiency n-type Si solar cells with Al-alloyed rear emitter.