2019 EPFL doctorate Award - Finalist – Jérémie Werner
Special distinction from the selection committee to Jérémie Werner for his thesis “Perovskite/Silicon Tandem Solar Cells: Toward Affordable Ultra-High Efficiency Photovoltaics ?”
EPFL thesis n°8659 (2018)
Thesis directors: Prof. C. Ballif, Dr B. Niesen
Photovoltaics solar energy is one of the key renewable energy for the green energy transition necessary to reduce our dependence on polluting fossil fuels. Over 95% of the photovoltaic market is however dominated currently by silicon technologies, which show performance already very close to their theoretical limits. In this thesis, a new class of photovoltaic materials, called perovskites, were investigated as an add-on to silicon to build multijunction solar cells. This concept should allow the fabrication of solar modules with higher power density and reduced cost per watt.
In particular, this thesis has helped to develop specific deposition techniques for the perovskites to be coated conformally onto the silicon micron-sized pyramid surface. The device optics were one of the main focus of this thesis, with attention to reducing parasitic absorption losses through the development of more transparent electrodes, adapted charge transport materials and careful device layer stack optimization. The perovskite absorber layer was also the subject of intense work to tune its optoelectronic properties, improve its growth quality and enhance its stability. During the 4 years of this work, several devices with world record efficiency were demonstrated as single junction semitransparent perovskite cells, as 4-terminal perovskite/silicon tandem, as 2-terminal monolithic tandem and triple junction solar cells.