Green Chemistry Preparation of P-N Junction Photoelectrode(2/2)

Utilize the solar energy efficiently is one of the most important tasks for every country. No matterwhether the solar energy is transformed into electricity, heat or chemical energy, a suitable medium to absorband store the solar energy is required. One of the green processes to transform solar energy into chemicalenergy is to use semiconductor photocatalyst. Take water splitting for example, when the semiconductor hasa suitable band gap, and right conduction band and valence band edges, the excited carriers gain enoughpotential to oxidize/reduce water and species presented in the electrolyte. Hydrogen and oxygen then can beproduced without any CO2 emission and hazardous waste. In the ideal condition, the hydrogen productionefficiency can reach 10% with the semiconductor of the band gap of 2.3 eV. Unfortunately, the real efficiencyis far below this value. The reasons are the following: 1. low excited carrier separation, 2. short carrierdiffusion length, 3. the small absorption/specific surface area, and 4. the slow reaction rate of the interface. Inthis proposed research, our approach involves the development of green pyrolysis to deposit semiconductorthin films, and generate homo- and heterojunction to create p-n junction. Based on our previous studies,different band positions and conductivity types of semiconductor (n-type and p-type) can be used as themodel system, to improve the electron-hole separation, and to investigate the carrier transfer mechanism.