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Solar cells and temperature coefficients

Sissel Tind Kristensen of the Faculty of Engineering and Science at the University of Agder has submitted her thesis entitled “Temperature coefficients and crystal defects in multicrystalline silicon solar cells“ and will defend the thesis for the PhD-degree Friday 11 December 2020. (Photo: Private)

The work has expanded the knowledge about how solar cells are influenced by the operating temperature.

Sissel Tind Kristensen

PhD Candidate

The disputation will be held digitally, because of the Corona covid-19-situation. Spectators may follow the disputation digitally.


Sissel Tind Kristensen of the Faculty of Engineering and Science at the University of Agder has submitted her thesis entitled “Temperature coefficients and crystal defects in multicrystalline silicon solar cells“ and will defend the thesis for the PhD-degree Friday 11 December 2020. 

She has followed the PhD-programme at the Faculty of  Engineering and Science with specilisation in Engineering Sciences, scientific field Renewable Energy.


Summary of the thesis by Sissel Tind Kristensen:

Solar cells and temperature coefficients: Understanding how multicrystalline silicon solar cells are influenced by temperature and crystal defects

Solar cells (or solar photovoltaics) are fascinating devices that convert sunlight directly into electrical energy that we can extract and use. Naturally, we want to extract as much power as possible from a photovoltaic device. In order to do so, we need to understand how it operates under various conditions.

The importance of studying operating conditions

When solar cells are fabricated, they are typically tested and optimized for a specific set of operating conditions (a specific temperature, light intensity and spectrum, etc.), including a cell temperature of 25°C.

However, when solar cells are connected to form a module and installed on a field or a rooftop, the operating temperature can vary substantially from 25°C.

At most locations worldwide, operating temperatures are much higher, which causes the output power from the solar cells and modules to decrease. This decrease in power is quantified using a parameter called the temperature coefficient.

It is very important to understand the influence of temperature on solar device performance for two main reasons.

  • First, it is necessary to accurately predict how much power a photovoltaic plant will produce during its lifetime and at various periods during the year.
  • Second, it enables the optimization of solar cells for different climatic conditions.

Crystal defects

My PhD work has studied one aspect of why and how solar cells are influenced by temperature, investigated through experiments and modeling.

During my PhD, I have studied solar cells made from multicrystalline silicon, which is the most common material used for industrial applications.

The multicrystalline silicon material is not a perfect crystal but contains structural defects and impurity atoms, commonly referred to as crystal defects.

Temperature coefficients

This PhD work has shown that the temperature coefficient of a multicrystalline silicon solar cell is partly determined by the presence of crystal defects.

Additionally, the work has uncovered the individual contribution from different defect types and found an especially interesting contribution from one type of crystal defect called a dislocation.

A novel characterization technique has been developed during the project which can obtain images of silicon wafers at various temperatures.

This enables a better understanding of how the performance varies across a photovoltaic device at various temperatures.

Finally, a numerical model has been developed, which makes it possible to predict the temperature coefficient of a solar cell from the knowledge of the defects present in the material.

Increased understanding of device physics and more accurate power predictions

The work has expanded the knowledge about how solar cells are influenced by the operating temperature.

This increases the understanding of the device physics of solar cells and ultimately enables more accurate power predictions under realistic operating conditions.


Disputation facts:

The trial lecture and the public defence will take place online, via the Zoom conferencing app (link below)

Professor Henrik Kofoed Nielsen, Department of Engineering Sciences, Faculty of  Engineering and Science, University of Agder, will chair the disputation.

Trial lecture at 10:15 hours
Public defense at 12:15 hours

Given topic for trial lecture: "Current challenges and opportunities for silicon crystallization processes: A review of both monocrystalline and multicrystalline processes"

Thesis Title: “Temperature coefficients and crystal defects in multicrystalline silicon solar cells

Search for the thesis in AURA - Agder University Research Archive, a digital archive of scientific papers, theses and dissertations from the academic staff and students at the University of Agder.

The thesis is available here:




The CandidateSissel Tind Kristensen (1991, Ringkøbing, Denmark) Bachelor of Science (B.Sc.) in Technical Physics, Aarhus University (2014), Master of Science (M.Sc.) in Physics, Aarhus University (2016).


First opponent: Research Scientist Olivier Dupré, CEA Liten, France

Second opponent: Professor Marisa di Sabatino Lundberg, Department of Materials Science and Engineering, NTNU

Professor Kjell Gunnar Robbersmyr, Department of Engineering Sciences, UiA, is appointed as the administrator for the assessment commitee.

Supervisors were Associated Professor Rune Strandberg, UiA (main supervisor) and Professor Tor Oskar Sætre, UiA (co-supervisor)


What to do as an audience member:

The disputation is open to the public, but to follow the trial lecture and the public defence, which is transmitted via the Zoom conferencing app, you have to register as an audience member.

We ask audience members to join the virtual trial lecture at 10:05 at the earliest and the public defense at 12:05 at the earliest. After these times, you can leave and rejoin the meeting at any time. Further, we ask audience members to turn off their microphone and camera and keep them turned off throughout the event. You do this at the bottom left of the image when in Zoom. We recommend you use ‘Speaker view’. You select that at the top right corner of the video window when in Zoom.

Opponent ex auditorio:

The chair invites members of the public to pose questions ex auditorio in the introduction to the public defense, with deadlines. Questions can be submitted to the chair, Henrik Kofoed Nielsen on e-mail henrik.kofoed.nielsen@uia.no