I want to know the simple exact and easy to understand scientific logic of the phenomenon involved for the water dissociation in the photo catalytic cell.
Attached herewith Research Article links that will help you to understand scientific logic of the phenomenon involved for the water dissociation in the photo catalytic cell.
01. Article Advances in Photocatalytic CO2 Reduction with Water: A Review
When you illuminate your material, holes are created in the VB and the electrons pass to the CB. In contact with water, and since you are manipulating an n-type semiconductor, the electrons will pass through the metallic ohmic contact at the back of the electrode while the holes in the VB will migrate to the electrode-water interface. These holes play the role of oxidation sites : H2O (+holes) > 1/2 O2 + 2H+ (if your electrolyte solution is acidic tending to neutral). The H+ will be reduced by the electrons at the cathode. This how the holes play oxidative role at the photo-anode/water interface.
Consult in particular Chapter 11 of [1]. The underlying physics is that which is taught in courses on solid-state physics, on the subjects of semiconductor-semiconductor and semiconductor-metal junctions. Here one has two junctions, between a semiconductor and a redox material and this redox material and a metal. The entire system can then be considered under the conditions of open- and closed circuit.