Relaxor Solar Cell Absorbers
Final Report Abstract
Absorbers are the most important material component in solar cells, because they convert light into electric charge carriers. They must fulfill a number of material requirements for high performance: They must provide an appropriate band-gap, i.e. the proper semiconductor properties to match the energy of the incoming light, high charge carrier mobility and lifetime, high charge carrier output, appropriate work function, which is necessary to get the charges out of the solar cell, and an appropriate design for light capturing. Classical semiconductors necessitate exclusive crystal purification techniques removing defects to very low concentrations in order to warrant these requirements. Research into other material classes, less demanding with respect to material purity, has been going on over decades. In this project we tried to understand charge carrier mobility in relation to dielectric screening in oxide perovskites. It was anticipated that the screening by polarons as well as by the relaxor-state of the material both contribute to a long lifetime of charge carriers. The project aimed at tuning the band gap of existing relaxor systems towards the optimum for the solar spectrum (around 1.3 eV). The promising candidate relaxor system PbFe0.5Nb0.5O3 (PFN) was reported to possess a band gap of around 1.0 eV. The chemical versatility of the perovskites was considered to allow for tailoring the band-gap and the work function by cation doping. Furthermore, the ferroelectric state of this material system promised to allow for easy charge separation. Precursor ceramics and nanoparticles were developed in the project. Highly textured thin films of around 100 nm thickness were successfully manufactured on conducting substrates of strontium tianate-strontium ruthenate using the pulsed laser deposition technique. The films were very homogenous and nearly epitaxial. It turned out that PFN is a very good absorber in the UV light spectral range, but the extension into the visible as claimed in literature proved to be wrong. The anticipated manufacturing of broad range ferroelectric solar cells was hindered by this inadequate band-gap and numerous technical problems including the pandemic. The conclusion of the project is that despite large hopes into this material, relaxor ferroelectric solar cell absorbers will not perform better than other known oxide perovskite ferroelectrics in the context of solar absorption. The project was funded as a joint project between the Centralesupélec in France and the University of Duisburg-Essen in Germany. In the project planning, much work was allocated to happen in both locations.
Publications
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Influence of synthesis route on the properties of lead iron niobate. 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF), 1-4. IEEE.
Bartek, Nicole; Shvartsman, Vladimir V.; Lupascu, Doru C.; Prah, Uros & Ursic, Hana
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Band Gap of Pb(Fe0.5Nb0.5)O3 Thin Films Prepared by Pulsed Laser Deposition. Materials, 14(22), 6841.
Bartek, Nicole; Shvartsman, Vladimir V.; Bouyanfif, Houssny; Schmitz, Alexander; Bacher, Gerd; Olthof, Selina; Sirotinskaya, Svetlana; Benson, Niels & Lupascu, Doru C.
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Influence of calcination and sintering temperatures on dielectric and magnetic properties of Pb(Fe0.5Nb0.5)O3 ceramics synthesized by the solid state method. Ceramics International, 47(16), 23396-23403.
Bartek, Nicole; Shvartsman, Vladimir V.; Salamon, Soma; Wende, Heiko & Lupascu, Doru C.
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Optical absorption by design in a ferroelectric: co-doping in BaTiO3. Journal of Materials Chemistry C, 10(1), 227-234.
Hao, Shenglan; Yao, Minghai; Vitali-Derrien, Gaëlle; Gemeiner, Pascale; Otoničar, Mojca; Ruello, Pascal; Bouyanfif, Housnny; Janolin, Pierre-Eymeric; Dkhil, Brahim & Paillard, Charles
