In-Situ Deposition and Growth of Cu2ZnSnS4 Nanocrystals on TiO2 Nanorod Arrays for Enhanced Photoelectrochemical Performance

Highly ordered TiO2 nanorod (TNR) arrays decorated with Cu2ZnSnS4 (CZTS) nanocrystals were prepared via a facile and effective method. The TNR arrays were synthesized using a hydrothermal treatment, and the CZTS nanocrystals were deposited by a three-step successive ionic layer adsorption and reaction (SILAR) technique followed by annealing in a sulfur atmosphere. The morphology, structure, composition, optical, and the photoelectrochemical (PEC) properties of the CZTS/TNR arrays were investigated in detail. The results demonstrate that the CZTS/TNR arrays can effectively facilitate photoinduced carrier transport, reduce the recombination rate of electron-hole pairs, and as a result demonstrate improved light absorption properties and PEC performance. The CZTS/TNR arrays sensitized with 7 SILAR cycles showed a maximal photocurrent density of 2.17 mA/cm2 at 0 V and the longest electron lifetime of 47.39 ms, which is nearly 80 and 2.03 times higher than those of pure TNR, respectively. The improvement in performance can be attributed to the high absorption coefficient and narrow bandgap of CZTS and the type-II nanoheterostructures with a staggered alignment of band edges present at the heterointerface. Surface passivation with ZnS resulted in a further improvement in PEC performance in comparison to the untreated CZTS/TNR arrays with values of 2.53 mA/cm2 and 59.77 ms for the maximal photocurrent density and longest electron lifetime, respectively.