The Transformation of Chemical into Electrical Potential in Solar Cells: a Contact Issue
Uwe Rau a
a IEK-5, Forschungszentrum Jülich, IEK5-Photovoltaics
Online School
Proceedings of Online School on Fundamentals of Emerging Solar Cells (PVSCHOOL)
Online, Spain, 2021 February 10th - 12th
Organizers: Bruno Ehrler, Thomas Kirchartz and Elizabeth von Hauff
Invited Speaker, Uwe Rau, presentation 005
DOI: https://doi.org/10.29363/nanoge.pv school.2021.005
Publication date: 29th January 2021

The generation of electron-hole pairs by solar photons and the resulting non-equilibrium excess concentration of those charge carriers is the driving force behind the photovoltaic action of solar cells. However, in order to generate electrical power, the charge carriers must (i) build up a photovoltage and (ii) must be continuously extracted to provide a photocurrent. This task leads to the question of contacts and the concept of contact selectivity in solar cells because it is at the contacts where both, the photovoltage as well as the photocurrent, are generated. Thus, whereas the non-equilibrium chemical potentials of electrons and holes can be looked at as the ‘engine’ driving the solar cells, we must look at the contacts as the ‘gear’ that transforms this undirected power into electrical power with a clearly defined polarity of the electrical terminals. The present contribution will clarify how this transformation occurs physically and by which equation it is dominated.

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