Enhancement of thermoelectric properties of sulphurized CZTS nano-crystals by the engineering of secondary phases

In this manuscript, we have explored the potential of Copper Zinc Tin Sulfide (CZTS) nano-crystals for thermoelectric power generation application by the engineering of secondary phases. CZTS nano-crystals were grown on various substrates (crystalline silicon (c-Si), multi-crystalline silicon (mc-Si), Soda Lime Glass (SLG) and Indium Tin Oxide (ITO) coated glass) using sol-gel solution technique. The grown samples were sulphurized in tube furnace at 500C for 20 min under vacuum. It was observed that sample grown on me-Si has highest Seebeck coefficient of 667 mu V/C-0 while sample grown on ITO substrate has the lowest value of Seebeck coefficient (70 mu V/C-0) at measurement temperature 100 degrees C. The reported high Seebeck coefficient of CZTS/mc-Si sample is related to the emergence of secondary phases. To verify this argument, we have performed XRD, Raman spectroscopy and UV/Visible measurements. XRD data revealed the presence of (112), (103) and (220) phases of CZTS in all samples but CZTS/mc-Si and CZTS/c-Si samples demonstrated additional phases related to secondary phases. Raman spectroscopy was also used to verify the presence of secondary phases in CZTS/mc-Si. Raman measurements showed that all samples consisted of CZTS vibration mode at 329 cm(-1) but CZTS/mc-Si and CZTS/c-Si have additional secondary phases due to CuxS, CuSnS and SnxS vibration modes. UV-Vis data also verified our argument that Seebeck coefficient was enhanced due to secondary phases engineering using various substrates for CZTS growth.