Size-dependent performances in homogeneous, controllable, and large-area silicon wire array photocathode

For photoelectrochemical (PEC) photoelectrodes composed by semiconductor wire arrays, the precisely designed wires play a crucial role in regulating the photoelectrochemical performances; however, an experimental evaluation of the size effect for high PEC performances relies on a controllable fabrication of the wires by preferentially the cost-effective and large-area method. Here, the fabrication of large-area and homogeneous silicon wire arrays with a good size controllability is realized by using the nanosphere lithography, inductively coupled plasma-reactive ion etching, and metal-catalyzed electroless etching. It is verified that the effects of the wire length/diameter on the PEC responses and carrier collection can be completely different for the PEC systems with or without surface passivation. Compared to the case with a relative-small length, the silicon wire array photocathode with a relative-large length shows the inferior (superior) PEC performances before (after) surface passivation (e.g., the saturated photocurrent density under AM 1.5G irradiation is significantly improved from 18.2 to 35.6 mA cm−2); moreover, a substantial anodical shift of the onset potential up to 0.95 V is realized for only increasing the wire diameter. The underlying mechanisms are revealed through analyzing the optical absorption, surface recombination, surface catalytic activity, and spatial flux density of the photogenerated carriers.