The Impact of Hot Injection Reaction Temperature on the Properties of Cu₂ZnSnS₄ Nanocrystal Thin Films for PV Devices

Cu2ZnSnS4 (CZTS) is a p-type absorber layer semiconductor, which is a promising candidate material for advanced solar cell devices. CZTS nanoparticle thin films were synthesized via the hot-injection spin-coating method. Nanoparticle inks were deposited on soda lime glass substrates. Different reaction temperatures during synthesis were investigated by using X-ray diffraction (XRD), focused ion beam microscopy (FIB-SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and Ultraviolet-visible spectroscopy to study the effects of the synthesis reaction temperature on CZTS thin films. The energy band-gap decreased with increasing reaction temperatures from 1.55 to 1.34 eV for the temperature range 225 degrees C-300 degrees C. These energy bandgaps show values close to the optimum for a CZTS solar cell device. XRD confirmed the kesterite structure, which is the preferred structure in CZTS for high efficiency PV device performance. In addition, a clear increasing trend of the scattering domain size with the reaction temperature is found to be in good agreement with the FIB-SEM images. Raman spectra showed no secondary phases. EDS of thin films demonstrated compositions consistent with start-up precursor ratios (Cu-poor Zn-rich composition). And 250 degrees C was identified as the most suitable reaction temperature for CZTS devices.