Excited State Dynamics Dependence on Variable Size of Nanostructured Cu2ZnSnS4 (CZTS)

The question the proposed research aims to address is the excited state dynamics dependence on variable size of nanostructured Cu₂ZnSnS₄ (CZTS). CZTS is a p-type (positively doped), Earth-abundant, and non-toxic semiconducting material. The short electron diffusion length of CZTS increases the difficulty of incorporation of the material into photovoltaic cells. However, high surface area CZTS nanostructures are well suited for photocatalytic surface reactions such as water reduction when employed in mesoscopic architectures. The mesoscopic donor-acceptor architecture substantially reduces the necessary diffusion length of the electrons (minority carriers) from the particle core to its surface where the photocatalytic reactions take place. The thermodynamic potential of the conduction band electrons is more than sufficient to drive water reduction, approximately -1.2 eV.

This research first aims to probe the excited state lifetime dependence on CZTS particle size. Second, we aim to assemble donor-acceptor architectures with NiO (p-type) as hole acceptor from CZTS to promote interfacial charge separation. Ultrafast laser spectroscopy was used to measure the dynamics of quantized CZTS nanocrystals prepared by hot injection method. In addition to assembling CZTS onto NiO, we also deposited the CZTS quantum dots on an insulating material to ascertain the hole transfer kinetics. It was found that the excited state lifetime decreases as the CZTS particle size decreases. We also present our preliminary results on the hole transfer from CZTS to NiO.