Nanocomposites and nanomaterials

Raman characterization of Cu2ZnSnS4-type nanocrystals obtained at different parameters of colloidal synthesis 
Havryliuk Ye.O1, Kapush O.A.1, Dzhagan V.M.1, Yukhymchuk V.O.1, Valakh M.Ya.1
1 V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, 41 pr. Nauki, 03028, Kyiv, Ukraine
E-mail: evgenko93@isp.kiev.ua

Up to date, more than 85% of solar panels use Si as an absorbing layer. However, due to this material has non-direct bandgap, a rather thick layer is required for absorbing sunlight effectively. In addition, the production of silicon-based solar panels is not environmentally friendly. For the last few years significantly growth of CdTe- and CIGS-based thin film solar cells are observed. But they are toxic and expensive, respectively. That's why one of the world's leading fields of research is finding alternative to Si materials that are environmentally friendly, with direct bandgap, and inexpensive. The materials of the Cu2ZnSnS4 (CZTS) family have all the necessary parameters. They have direct band gap 1,4 – 1,6 eV and absorption coefficient ~104. The constituent elements are widespread and non-toxic. Eco-friendly low-temperature colloidal synthesis of CZTS nanocrystals (NC) makes these materials promising for use in the so-called third generation of a truly thin-film photovoltaics. However, there are a number of issues that need to be overcome to achieve a conversion efficiency of solar energy into electricity sufficient for commercial use. For example, due to the multiple constituent components of these compounds, there is a high probability of the formation of internal defects in the form of vacancies, antisite defects, as well as the formation of secondary phases of binary and ternary compounds. This leads to a decrease of the crystalline quality and consequent decrease of the conversion factor.
In this work, the effect of different parameters of low-temperature colloidal synthesis on the crystallinity quality and stability of the obtained CZTS NCs was investigated. It was found that by using our modified technique of low-temperature colloidal synthesis withthioglycolic acid as stabilizer, NCs of good crystallinity can be obtained without post-synthesis thermal treatment., In addition, the  synthesis of CZTS NC in presence of CdTe, Au or Ag nanoparticles was investigated. It was shown that the crystalline quality of CZTS NC was improved by the adding of CdTe, whereas no effect was observed with the adding of Ag and Au. The latter novel hybrid nanosystems still needs further research.