Optimization of Cu2ZnSnS4 Nanocrystal Composition and Thin Film Fabrication for Photovoltaic Applications

In this work Cu2ZnSnS4 (CZTS) nanocrystals (NCs) were prepared via a solvothermal, one-pot method. Given that the composition affects the electronic properties of this p-type semiconductor, comparative compositional analysis was done from various designed and synthesized analogues. EXAFS studies indicated that the stoichiometries with lower Cu-contents (Cu Sn+Zn The effects of Cu were further studied, using Cu-poor and Cu-stoichiometric NCs.This time the precursor content of Zn was also increased to yield samples with Zn rich compositions. NCs in which the Cu concentration was below stoichiometric (Cu1.8Zn1.1Sn1.0S4.8) were more crystalline and yielded a higher photoresponse (~53 μA/cm2). The compositionally optimized CZTS NCs were then deposited using four experimental approaches to yield CZTS thin films: (1) drop cast, (2) joule heating, (3) dip coating and (4) spin coating. The depositions were carried out on FTO and Mo-coated substrates. Comparably, films fabricated using the spin coat method, consistently exhibited a good photoresponse (FTO=69-75 μA/cm2, Mo=60-77 μA/cm2), along with smoother surfaces with less carrier traps. The NCs deposited in this manner were further used for device fabrication. The preliminary results of the final device yielded a low efficiency indicating that optimization of the processes post-deposition, are required