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Ville Polojärvi has been awarded for the best doctoral thesis of the year 2016 by Photonics Finland

TUT researcher Ville Polojärvi has won the prize of the best doctoral thesis in 2016 awarded by Photonics Finland. Polojärvi’s doctoral thesis deals with III-V semiconductor solar cells electrical, optical and structural properties.
Ville Polojärvi Presenting his work at Optics & Photonics Days in Oulu Finland, May 29–31 2017.
Ville Polojärvi Presenting his work at Optics & Photonics Days in Oulu Finland, May 29–31 2017.

Ville Polojärvi studied in his doctoral thesis “Novel III-V Heterostructures for High Efficiency Solar Cells: Studies of Electrical and Optical Properties” various kind of semiconductor heterostructures, which could potentially be applied in high-efficiency solar cells. Examples of such heterostructures are semiconductor quantum dots, quantum wells, and lattice matched dilute nitride materials consisting of Ga, In, N, As, and Sb.

Polojärvi’s work enabled higher conversion efficiencies for the III-V semiconductor solar cells designed, fabricated and processed at the TUT. Such multijunction solar cells are applied in space satellites and in terrestrial concentrated photovoltaics applications. Conversion efficiency is a critical parameter in both abovementioned applications, because all the other costs than fabrication of the solar cell itself scales down with the conversion efficiency. In space, especially high power-to-mass ratio and radiation hardness are essential.

One of the key research areas in Dr. Polojärvi’s thesis is related to the properties of dilute nitride GaInNAsSb semiconductor material. This material can be ultimately used for harvesting sun’s infrared radiation very efficiently. In order to achieve very high conversion efficiency major part of the solar spectrum, from UV radiation to infrared, must be exploited.

Dr. Polojärvi’s doctoral thesis is part of the active solar cell research at Optoelectronics Research Centre (ORC) in TUT funded by, e.g., European Research Council, the Finnish Funding Agency for Technology and Innovation (Tekes), European Space Agency, and various foundations. Currently eleven people work on solar cells at ORC.

Because of long-term research conducted by the top scientists, solar cells made in ORC/TUT are top class globally, and their conversion efficiencies are comparable to the best cells in the world. Best space solar cells made in Tampere have over 30 percent conversion efficiency, when typical commercial space solar cells conversion efficiency is slightly less than 30 per cent. TUT’s conversion efficiency record for concentrated photovoltaic solar cells is over 40 per cent, but the goal is to exceed 50 per cent limit and bring the title of the most efficient solar cell in the world to Tampere.

The best doctoral thesis award in the year 2016 based on three criteria:

1. Scientific impact (quality and number of journal papers used as basis for the thesis);

2. Societal impact (relevance in terms of real-world applications);

3. Quality of the manuscript (overall presentation, amount of work etc.)

Ville Polojärvi works as a postdoctoral researcher in Laboratory of Photonics, Optoelectronics Research Centre, in Professor Mircea Guina’s group. Dr. Polojärvi is head of the solar cell processing group and is responsible for the solar cell processing and process development. He is also doing research on, e.g., different semiconductor materials and surfaces, nanostructures and thin films.

Doctoral thesis: Novel III-V Heterostructures for High Efficiency Solar Cells: Studies of Electrical and Optical Properties

Photonics Finland

News submitted by: Tuuli Laukkanen
Keywords: science and research, doctoral thesis, award, photonics