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Dong H.,Karlsruhe Institute of Technology | Schnabel T.,Zentrum fur Sonnenenergie und Wasserstoffforschung Baden Wurttemberg ZSW | Ahlswede E.,Zentrum fur Sonnenenergie und Wasserstoffforschung Baden Wurttemberg ZSW | Feldmann C.,Karlsruhe Institute of Technology
Solid State Sciences | Year: 2014

Cu2ZnSnS4 kesterite nanoparticles (CZTS) with a particle diameter of 10-20 nm are prepared by a polyol-mediated synthesis with diethylene glycol as the liquid phase. The polyol - a high-boiling multidentate alcohol - allows controlling the particle size and agglomeration as well as preparing readily crystalline nanoparticles. The as-prepared kesterite nanoparticles exhibit an overall composition of Cu1.56Zn 1.29Sn1.16S4.59 and a band gap of 1.37 eV. As a first test, thin-film solar cells are manufactured after layer deposition of the as-prepared CZTS nanoparticles and conversion to Cu2ZnSn(S,Se) 4 (CZTSSe) via gas-phase selenization. The volume increase of about 15% due to the CZTS-to-CZTSSe conversion supports the formation of a dense layer, reduces the interparticulate surfaces and leads to a reduction of the band gap to 1.14 eV. The chemical composition of the as-prepared CZTS nanoparticles and of the deposited CZTSSe thin film prior and after selenization are studied in detail by energy-dispersive X-ray spectroscopy, Raman spectroscopy and X-ray fluorescence analysis. All these methods confirm the intended copper-poor and zinc-/tin-rich CZTS/CZTSSe composition. The resulting thin-film solar cells show an open-circuit voltage of 247.3 mV, a short-circuit current density of 21.3 mA/cm2, a fill factor of 41.1% and a power-conversion efficiency of 2.2%. © 2014 Elsevier Masson SAS. All rights reserved. Source

Dong H.,Karlsruhe Institute of Technology | Quintilla A.,Zentrum fur Sonnenenergie und Wasserstoffforschung Baden Wurttemberg ZSW | Cemernjak M.,Zentrum fur Sonnenenergie und Wasserstoffforschung Baden Wurttemberg ZSW | Popescu R.,Karlsruhe Institute of Technology | And 3 more authors.
Journal of Colloid and Interface Science | Year: 2014

Selenium nanoparticles with diameters of 100-400nm are prepared via hydrazine-driven reduction of selenious acid. The as-prepared amorphous, red selenium (a-Se) particles were neither a stable phase nor were they colloidally stable. Due to phase transition to crystalline (trigonal), grey selenium (t-Se) at or even below room temperature, the particles merged rapidly and recrystallized as micronsized crystal needles. As a consequence, such Se particles were not suited for layer deposition and as a precursor to manufacture thin-film CIS (copper indium selenide/CuInSe2) solar cells. To overcome this restriction, Se@CuSe core@shell particles are presented here. For these Se@CuSe core@shell nanoparticles, the phase transition a-Se→t-Se is shifted to temperatures higher than 100°C. Moreover, a spherical shape of the particles is retained even after phase transition. Composition and structure of the Se@CuSe core@shell nanostructure are evidenced by electron microscopy (SEM/STEM), DLS, XRD, FT-IR and line-scan EDXS. As a conceptual study, the newly formed Se@CuSe core@shell nanostructures with CuSe acting as a protecting layer to increase the phase-transition temperature and to improve the colloidal stability were used as a selenium precursor for manufacturing of thin-film CIS solar cells and already lead to conversion efficiencies up to 3%. © 2013 Elsevier Inc. Source

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