Laboratoire de Physique des Interfaces et des Couches Minces

CNRS - École polytechnique - Institut Polytechnique de Paris

Low temperature PECVD epitaxy for tandem c-Si/c-Si solar cells

Plasma-enhanced chemical vapour deposition of silicon thin films is currently used in various processing steps of c-Si solar cells such as a-SiN:H passivation and antireflection coating, heterojunction solar cells, surface texturing, etc. Interestingly, PECVD processes have been shown to be capable of growing epitaxial Si and SiGe layers at low temperature and their application to solar cells has been successfully demonstrated at LPICM laboratory [1-3].

The objective of this internship will be to put into practice a recent modelling work [4] in which the authors show that tandem c-Si/cSi solar cells have the potential to achieve over 30% conversion efficiency. The facilities at LPICM seem to be ideally suited to put this theoretical work into practice.

In order to get familiar with the project, the student will be involved in the PECVD deposition of the epitaxial films, their structural characterization via spectroscopic ellipsometry and Raman spectroscopy as well as their electronic characterization mainly via photoluminescence. The optimized layers will be applied to solar cells as indicated in the figure below. The fabricated solar cells will be characterized by means of their dark and light J(V) measurements as well as Quantum Efficiency measurements. A particular attention will be paid to the development of the tunnel junction connecting the thick wafer based c-Si solar cell, on which the top and thin epitaxial cell will be deposited by PECVD. The figure below, taken from [4], shows the band diagram of the targeted structure. Modelling will be used in parallel to guide the experimental development of the tandem structure.

Schematic band diagram of a monolithic tandem device under operating conditions (illumination and V < Voc). Energies and distances not to scale, from reference [4]
Contacts: Prof. Pere Roca i Cabarrocas –


[1] M. Chrostowski, R. Peyronnet, W. Chen, N. Vaissiere, J. Alvarez, E. Drahi, and P. Roca i Cabarrocas: “Low temperature epitaxial growth of boron-doped silicon thin films”. AIP Conference Proceedings 1999 (2018) 070001.

[2] Marta Chrostowski, José Alvarez, Alessia Le Donne, Simona Binetti, and Pere Roca i Cabarrocas : “Annealing of Boron-Doped Hydrogenated Crystalline 2 Silicon Grown at Low Temperature by PECVD”. Materials 2019, 12, 3795; doi:10.3390/ma12223795.

[3] Cyril Leon, Sylvain Le Gall, Marie-Estelle Gueunier-Farret, Jean-Paul Kleider, Pere Roca i Cabarrocas : “Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates”. EPJ Photovoltaics 11, 4 (2020).

[4] F.-J. Haug and C. Ballif: “A recalculation of the efficiency limit in crystalline Si/Si tandem solar cells”. Solar Energy Materials & Solar Cells 224 (2021) 111008.

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