Photocurrent improvement in nanocrystalline Cu2ZnSnS4 photocathodes by introducing porous structures

Cu2ZnSnS4 (CZTS) is a potential low-cost photocathode material for solar water splitting. In this study, we prepare dense and porous nanocrystalline Cu2ZnSnS4 films by a facile metal organic decomposition (MOD) method. The porous structures are adjusted by varying the amount of thiourea in the precursor solution. The porous CZTS photocathode yields 3 times higher photocurrent than that of the dense electrode. Thermogravimetric/differential thermal analysis shows that the porous structure comes from decomposition of excess thiourea. Different characterization methods, such as X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, SEM and UV-vis-NIR transmission, have been carried out to analyze the mechanism of photocurrent improvement. The results suggest that the dense and the porous CZTS photocathodes have similar crystallinity, composition, thickness and light absorption. The relative electrochemical active area indicates that shortening of the electron transport distance is a possible reason for photocurrent improvement in the porous CZTS photocathode.