Understanding and modelling the electronic transport properties of Poly-Si Passivating Contacts by Low-Temperature I-V Characterization

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Demystifying the carrier transport through novel passivating contact layers

With the challenges posed by the global warming and an ever-increasing energy demand of the world’s population, transitioning to energy harvesting from renewable sources is an essential step to be taken for a sustainable future. While photovoltaics (PV) show great promise for facilitating this transition with its steadily increasing installed power generation capacity and by allowing an already low levelized-cost-of-electricity, further price reduction is necessary to raise the share of PV in the global energy mix and to replace the fossil fuels. One of the most viable means for such price reduction is improving the power conversion efficiency of the state-of-the-art solar cells produced by the PV industry. With its expertise in PV and cutting-edge infrastructure, Imec’s PV department works towards developing highly-efficient solar cells fabricated by methods feasible for the PV industry.

This master’s thesis is concerned with investigating polycrystalline silicon (poly-Si) passivating contacts for solar cells, a contact structure that recently gained a lot of attention and is poised to be included in industrial solar cells in the near future. These contacts consisting of a stack of an ultrathin silicon oxide (SiOx) and heavily-doped poly-Si have been shown to minimize the recombination of minority carriers at the metal-silicon interface after their generation by the absorption of sunlight. Simultaneously, these contacts allow uninhibited extraction of the majority carriers to an external circuit for electricity generation. Thus, these contacts reduce both the recombination and resistive losses, thereby yielding higher solar cell efficiencies.

Even though very high efficiencies up to 26.1% were demonstrated with cells incorporating poly-Si contacts, the mechanism of the excellent passivation provided by these or specifically of the carrier transport through these structures are still disputed. There is, in fact, still no consensus whether current flow through the pinholes in the SiOx or tunneling through the SiOx layer is dominant. During this thesis, samples with a metal (rear)/c-Si (substrate)/SiOx/poly-Si/metal (front) stack will be fabricated in Imec’s clean room, the temperature-dependent dark I-V characteristics of the samples will be measured at a range of very low to higher temperatures using equipment at Imec. During the analysis, the I-V characteristics will be investigated to find out if features characteristic to tunneling are present. A similar study to determine the specific contact resistance as a function of temperature will follow, based on temperature-dependent transfer length measurements, on samples featuring contact pads of different areas. All in all, both studies will provide fundamental insight into the current flow through poly-Si passivating contacts.

The student is required to have a solid background in materials and is expected to be motivated in semiconductor device characterization. During this thesis, the student will acquire fundamental understanding about silicon solar cells and poly-Si passivating contacts by a literature study. Moreover, the student will gain valuable experiences in device characterization and fabrication and thus be well-positioned for their future endeavors.


Type of project: Internship, Thesis

Duration: 6-12 months

Required degree: Master of Engineering Technology, Master of Science, Master of Engineering Science

Required background: Energy, Nanoscience & Nanotechnology, Physics

Supervising scientist(s): For further information or for application, please contact: Meric Firat (Meric.Firat@imec.be)

Allowance only for students from a non-Belgian university

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