A number of lectures will be presented. The lectures describe a number of active research areas undertaken in Professor Hilal’s research lab. The lectures describe earlier achievements and future prospects in the areas of semiconductor electrodes and their application in solar energy processes. Semiconductors are being used in solar energy in different forms. Monolithic materials are being used in photovoltaic (PV) as homo-junctions, hetero-junctions or tandem systems. Monolithic electrodes are also used in photo-electrochemical (PEC) processes when brought in direct contact with suitable solutions. The solid/liquid interfaces behave as n-p (or p-n) junctions and can effectively be used like PV systems. Such electrodes suffer the shortcoming of being unstable under PEC conditions. Their conversion efficiencies are also lower than predicted in theoretical reports. Enhancing their conversion efficiency and stability can be achieved by simple techniques. This is one area where we have been active, and our results will be presented.
Due to their cost and advanced preparation processes, monolithic PV systems are being replaced by thin film electrodes. TiO2 and other stable wide band gap semiconductor materials have been extensively investigated. Unfortunately such systems demand UV radiations (with wavelengths shorter than 400 nm) which account to less than 5% of incident solar radiations. Sensitizing such systems using dye molecules or quantum dots is an active area, but again suffers many shortcomings. Narrower band gap materials are being widely considered recently for PEC applications due to their ability to function in the visible region (highly abundant in incident solar radiations). Metal chalcogenide thin films with the general formula (MnXm: where M is Cu, Cd, Zn, …; X is S, Se or Te) are heavily studied. Despite their many advantages, such as band gap suitability, ease to manufacture and ease to modify, such systems showed low conversion efficiency to many reasons. They also photo-degrade under PEC conditions. These labs have been active in finding simple ways to stabilize such systems and to increase their conversion efficiencies. We have shown that conversion efficiencies of up to 17% can be attained by modified metal chalcogenide thin film electrodes. This is far higher than the US-DOE expectations for the year 2020. For these purposes, we have modified the electrodes by a number of methods, including multi-layers deposition (using successive electrochemical and chemical bath depositions), coating with electro-active species inside polymers, annealing and cooling rate control. By these methods we have been able to control flat band potential values and charge transfer across the solid/liquid junction. We managed to prevent hole accumulation in the space charge region of the working electrodes. All PEC characteristics have been enhanced, including the fill factor, the short circuit photocurrent, the efficiency, the open circuit potential and the stability. A model will be presented to explain such enhancements.
Another active area has been enhancing quantum-dot semiconducting electrodes in water purification and disinfection. We have developed new ways to enhance efficiency and stability of such nano-size electrodes in environmental protection with solar light. Killing bacteria and completely mineralizing their residues has been achieved here for the first time. All these activities will also be presented.
Future prospects of research in these areas will be presented. Areas of collaboration and future project plans will be discussed. Involvement of new advanced materials such as grapheme sheets and carbon nano-tubes will be discussed. Coating the thin film electrodes by electro-active species trapped onto graphene will be jointly examined.