Asea Brown Boveri Ltd. (ABB) Award - 2023 - Laurie-Lou Senaud
Electrical Losses Mitigation in Silicon Heterojunction Solar Cells
EPFL thesis n°8648
Thesis director: Prof. Ch. Ballif
For her work on the optics and electronics of high efficiency heterojunction crystalline silicon solar cells, allowing the achievement of efficiencies over 25% with industry compatible processes.
To overcome the worldwide challenges of climate change, photovoltaics is foreseen to play a significant role in the world electricity production. Nowadays, single junction crystalline-silicon (c-Si) based solar cells hold the largest share of the global photovoltaic market. To achieve their maximum energy conversion efficiency, carrier-selective-passivating contacts have been demonstrated to be the most promising technologies. Among them, silicon heterojunction (SHJ) solar cells demonstrated record efficiency thanks to high c-Si bulk quality and excellent surface passivation. However, despite remarkable performance, the material layers used to build SHJ cells are at the origin of significant trade-offs between electrical and optical properties. The aim of this thesis is to accurately describe, quantify, and mitigate the electrical losses occurring in SHJ solar cells by means of advanced methodologies and characterization methods.
The outcomes of this work are manifolds. First, a generalized and unambiguous description of the concept of contacts is introduced, and a characterization methodology using two new approaches designed to independently track the physical properties of the material layers is proposed. Secondly, transfer length method measurements under variable illumination are demonstrated as a novel advanced characterization method to study the electrical transport losses. Finally, by engineering the electrical and optical properties of the material layers, impressive solar cells efficiencies are achieved.