Novel light-trapping structures for thin-film solar cells

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2018-09-14
Degree programme
94 + app. 58
Aalto University publication series DOCTORAL DISSERTATIONS, 145/2018
The thesis is devoted to the development of novel broadband light-trapping structures based on regular arrays of nanostructures and microstructures often referred in the modern literature as metamaterials. Our suggested light-trapping structures offer the gain in the optical efficiency of thin-film solar cells of several types without damaging their operational characteristics. These types of photovoltaic devices include thin-film solar cells based on amorphous silicon, organic and perovskite materials. In the first part, we present a metal light-trapping structure based on arrays of nanoantennas and report its theoretical and experimental studies. We reveal unusual eigenmodes in arrays of metal elements with domino-like proportions and show that in the optical range of frequencies they may composite a broad frequency band comparable with the operation band of a realistic solar cell. We experimentally confirm the existence of these modes and theoretically prove their light-trapping functionality. We design the optimal array of metal nanoantennas supporting these modes and theoretically demonstrate the enhancement of the useful absorption for a realistic organic solar cell. Finally, we present experimental results demonstrating an increase of the overall power conversion efficiency granted by our light-trapping structure compared to the reference solar cell with a conventional design. In the second part, we discuss novel all-dielectric light-trapping structures and report the results of full-wave numerical simulations. For amorphous silicon-based thin-film solar cell, we study the suppression of both reflection and transmission granted by the following systems: a flat antireflection coating, an array of densely packed polystyrene nanospheres, and arrays of nanovoids (cylindrical and tapered shape, both in the PMMA layer). We optimize the geometrical parameters to obtain the highest absorption in the photovoltaic layer and reveal light-trapping properties of these structures. Finally, we suggest and study a universal light-trapping structure for solar cells of 3rd generation. The structure consists of an array of dielectric truncated cones serving as the tapered optical waveguides for the incident light and optically connected to the thin-film solar cell through the holes in the metal film (e.g., Au). We theoretically show the advantages of our solution with respect to known analogs: it grants a gain in the PV absorption both in case of the organic thin-film SC (more significant) and perovskite thin-film SC (less significant but still noticeable). The existing techniques allow us to fabricate such a structure rather simply and quickly without involving expensive materials or processes. We believe that the presented results are helpful for the further development of thin-film solar cells of these three types.
Supervising professor
Simovski, Constantin, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
Belov, Pavel, Prof., ITMO University, Russia
solar cells, light-trapping, nanoantennas, metamaterials
Other note
  • [Publication 1]: Pavel M. Voroshilov, Constantin R. Simovski. Leaky domino-modes in regular arrays of substantially thick metal nanostrips. Photonics and Nanostructures: Fundamentals and Applications, 20, 18-30, July 2016.
    DOI: 10.1016/j.photonics.2016.03.002 View at publisher
  • [Publication 2]: Ivan S. Sinev, Pavel M. Voroshilov, Ivan S. Mukhin, Andrey I. Denisyuk, Mikhail E. Guzhva, Anton K. Samusev, Pavel A. Belov, Constantin R. Simovski. Demonstration of unusual nanoantenna array modes through direct reconstruction of the near-field signal. Nanoscale, 7, 765-770, January 2015.
    DOI: 10.1039/C4NR04872E View at publisher
  • [Publication 3]: Pavel M. Voroshilov, Constantin R. Simovski, Pavel A. Belov. Nanoantennas for enhanced light trapping in transparent organic solar cells. Journal of Modern Optics, 61, 1743-1748, July 2014.
    DOI: 10.1080/09500340.2014.940019 View at publisher
  • [Publication 4]: Pavel M. Voroshilov, Victor Ovchinnikov, Alexios Papadimitratos, Anvar A. Zakhidov, Constantin R. Simovski. Light Trapping Enhancement by Silver Nanoantennas in Organic Solar Cells. ACS Photonics, 5,1767-1772, April 2018.
    DOI: 10.1021/acsphotonics.7b01459 View at publisher
  • [Publication 5]: Pavel M. Voroshilov, Constantin R. Simovski, Pavel A. Belov, Alexander S. Shalin. Light-trapping and antireflective coatings for amorphous Si-based thin film solar cells. Journal of Applied Physics, 117, 203101, May 2015.
    DOI: 10.1063/1.4921440 View at publisher
  • [Publication 6]: Pavel M. Voroshilov Constantin R. Simovski. Affordable universal light-trapping structure for third-generation photovoltaic cells. Journal of the Optical Society of America B, 37, D77-D80, June 2017.
    DOI: 10.1364/JOSAB.34.000D77 View at publisher