Surface Modification of N-Gaas Semiconductor with Metalloporphyrin/ Polysiloxane Matrices Effect of Modification on : Band-Edge Positions, Short Circuit Current and Surface Stability in Aqueous Photoelectrochemistry

Hikmat S. Hilal's picture
Type: 
Thesis
Year: 
2001
Students: 
Muayad Masoud Mahmoud Masoud
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Surface Modification of N-Gaas Semiconductor with Metalloporphyrin/ Polysiloxane Matrices Effect of Modification on : Band-Edge Positions, Short Circuit Current and Surface Stability in Aqueous Photoelectrochemistry2.66 MB
Abstract: 
Semiconductor (SC) surfaces are currently being investigated as catalysts for solar energy utilization. In one of the most important applications of photoelectrochemical (PEC) cells, SCS are used as photocatslysts for water splitting. Unfortunately, there is no available SC that satisfies all the features of a good SC catalyst for PEC water splitting. Therefore, it is desired that the band edges of SC be shifted, mainly positively, to improve the charge transfer processes at the surface and to enhance the SC surface resistance against deterioration. We have developed a new technique to tailor the positions of SC band edges. Tetra (-4-pyridyl)porphyrinatomanganese(III)sulfate (MnP), existing in the form of Mnm and Mnu ion mixture, was embedded into a polysiloxane polymer matrix and was attached to the surfaces of n-GaAs wafers. The n- GaAs/polymer/MnP system was annealed under nitrogen and used for photoelectrochemical study in water/LiClO4 and Fe(CN)63'/Fe(CN)64` as a redox couple. The results indicated a positive shift in the value of the flat—band potential of the SC due to the presence of the MnP. Mott-Schotky plots indicated positive shift in the value of the flat-band potential. This was also manifested by shifting the values of the dark-current onset potential and the photocurrent open-circuit potential towards more positive values. Unlike earlier reports, the values of the short-circuit currents, measured with time of exposure, were significantly enhanced by modification. The modified surfaces were more stable, to photodegradation, than the unmodified surfaces while using high intensity illumination. The n-GaAs/polymer/MnP electrode showed higher cell efficiency than the unmodified.