Evolution pathways for the formation of Nano-Cu2ZnSnSe4 absorber materials via elemental sources and isophorondiamine chelation

This paper reports the preparation of Cu2ZnSnSe4 (CZTSe) nanocrystals via a method under nitrogen atmosphere at a temperature of 235 °C using elemental copper, zinc, tin, and Se powders as precursors, and isophorondiamine (IPDA) as a coordinating solvent. We investigated the influence of reaction time on the crystal structure, shape, particle size, optical properties, and composition of the nanocrystals. We also carried out a systematic study of the growth and evolution pathways of quaternary CZTSe nanocrystals in the IPDA solution. The reaction began with the formation of binary and ternary crystals, which subsequently transformed into Cu2ZnSnSe4 nanocrystals. These binary and ternary compounds dissolved during the course of the reaction to produce the molecular precursor used in the formation of monophasic Cu2ZnSnSe4 nanocrystals. Experimental results indicate that the phase changes in CZTSe nanocrystals are time-dependent. Spherical CZTSe nanocrystals with diameters in the range of 20-30 nm were obtained at 20 h. Characterization using X-ray diffraction (XRD) confirmed the as-synthesized CZTSe as single-phase quaternary nanocrystals with a stannite structure. The band gap energy of the as-synthesized CZTSe nanocrystals is 1.6 eV. The proposed process of synthesizing CZTSe nanocrystals is applicable to the production of inexpensive thin film solar cells using a relatively simple, low cost, and convenient coordinating solvent route.