Neutrons and photons in photovoltaic materials research
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2021-05-11 05:12
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SCHORR, S.. Neutrons and photons in photovoltaic materials research. In: Materials Science and Condensed Matter Physics, 13-17 septembrie 2010, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2010, Editia 5, p. 26.
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Materials Science and Condensed Matter Physics
Editia 5, 2010
Conferința "Materials Science and Condensed Matter Physics"
Chișinău, Moldova, 13-17 septembrie 2010

Neutrons and photons in photovoltaic materials research


Pag. 26-26

Schorr S.
 
Freie Universitat Berlin, Institut fur Geologische Wissenschaften
 
Disponibil în IBN: 12 aprilie 2021


Rezumat

Within the renewable energies photovoltaics, the direct conversion of sunlight into electrical energy, plays a key role. Thin film solar cells are considered the next generation of photovoltaics, because of their considerable cost reduction potential based in comparison with silicon solar cells through the minimization of material needed and processing techniques which allow a more efficient use of the module surface and a monolithic integration1. Amongst the most promising material options for thin film solar cells are compound semiconductors. Using ternary and quaternary chalcopyrite type compounds like Cu(In,Ga)Se2 as absorber material in the thin film solar cell results in the highest efficiencies in the laboratory scale (20.1%) as well as in the module production. In order to secure the long term development of compound semiconductor based thin film solar cells, alternative absorber materials like the kesterites Cu2ZnSnS4 and Cu2ZnSnSe4 were tested successfully (efficiencies up to 9.6%). These compounds are characterized by non-stoichiometry and the existence of intrinsic point defects (vacancies and anti sites), which influence the electronic properties of the material. A detailed knowledge of the structural parameters of the absorber material, especially cation order and disorder causing cation anti sites as well as the cation/vacancy distribution is the basis to understand structure property relations which are crucial for tailoring of high efficient solar cells. Regarding the elements Cu and Zn as well as Cu and Ga, their cations Cu+, Zn2+ and Ga3+ have the same number of electrons (28). Due to their similar scattering power in X-ray diffraction a precise differentiation between Zn2+ and Cu+ as well as Cu+ and Ga3+ on different structural sites is not possible by this method. But the neutron scattering lengths of these elements are different, thus neutron diffraction is the only possibility to answer the question of cation distribution. Temperature dependent structural phase transitions, linear thermal expansion coefficients, reaction kinetics and chalcogenization pathways are important to know for the successful growth of the absorber layers. Insitu high temperature diffraction experiments using synchrotron X-rays are the method of choice to gain a detailed knowledge on these properties. Within the talk the results of a number of neutron and synchrotron X-ray diffraction experiments on the chalcopyrites Cu(In,Ga)S2/Se2 as well as the kesterites Cu2ZnSnS4/Se4 covering a temperature range from 1.5 K to 1100°C will be presented. It will be shown, like the complementary use of neutrons and synchrotron Xrays results in a comprehensive picture of the different faces of the crystal structure of these next generation photovoltaic materials.