Optimising The Parameters For The Synthesis Of Cuin-Nanoparticles By Chemical Reduction Method For Chalcopyrite Thin Fil
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OPTIMISING THE PARAMETERS FOR THE SYNTHESIS OF CuInNANOPARTICLES BY CHEMICAL REDUCTION METHOD FOR CHALCOPYRITE THIN FILM PRECURSORS Matthias Schuster1, Stefan A. Möckel1, Rachmat Adhi Wibowo², Rainer Hock², Peter J. Wellmann1 1 Department Materials Science, Chair Materials for Electronics and Energy Technology, Friedrich-Alexander-University of Erlangen-Nürnberg, Martensstr. 7, 91058 Erlangen, Germany; ²Chair for Crystallography and Structure Physics, Friedrich-Alexander-University of ErlangenNürnberg, Staudtstr. 3, 91058 Erlangen, Germany.
ABSTRACT Roll-to-roll deposition techniques for the fabrication of chalcopyrite solar cells are of major interest and are a promising alternative to state of the art vacuum processes. However, for roll-to-roll processes the preparation of precursor materials like nanoparticle inks is a crucial point. In this work a study on the preparation technique of copper-indium intermetallic nanoparticles was conducted. The preparation of the nanoparticles is based on the chemical reduction of copper and indium cations with sodium borohydride. Different parameters are discussed regarding their influence on (1) size and shape of the nanoparticles, (2) Cu/In ratio within the synthesised nanoparticles and (3) yield of the synthesis. Results show a strong dependency of the Cu/In ratio of the nanoparticles and the yield of the synthesis on the synthesis parameters. The influence of different parameters like (a) the ratio of metal cations to BH4anions, (b) the Cu2+/In3+ cation ratio within the precursor solution and (c) the dropping rate of the copper-indium precursor solution are discussed. The Cu/In ratio within the nanoparticles can mainly be controlled by the Cu2+/In3+ cation ratio and the dropping rate of the copper-indium precursor solution. The yield of the synthesis shows saturation behaviour depending on the ratio of metal cations to BH4- anions. Shape and size of the nanoparticles are independent of the varied parameters. INTRODUCTION Chalcopyrite solar cells are a promising alternative to conventional silicon solar cells. Due to their high absorption coefficient layer thickness and thereby material usage can be reduced. Solar cells with an efficiency up to 20.3% [1] can be achieved by well-established fabrication processes like co-evaporation. However, to reduce fabrication costs non-vacuum processes are investigated [2]. Recently a lot of research was conducted on preparation methods using bimetallic CuIn nanoparticles for roll-to-roll processing of copper indium diselenide (CISe) solar cell absorbers [3–7]. Efficiencies of cells processed by this route range from 1.43% [3] to 7% [4]. However, for CISe thin-film solar cells the ratio of elements within the absorber layer is a critical point. Champion solar cells, which also incorporate gallium, were fabricated with a Cu-depleted composition [8]. The main reason for this composition is to avoid the formation of conductive copper-selenides which may shunt the solar cell.
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To avoid etching with KCN to remove these copper-selenides
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