Awodugba A O and Araromi D O
Keywords: Chemical bath deposition, film thickness, supersaturation, multiobjective functions genetic algorithm.
Abstract: Chemical bath deposition (CBD) has been adjudged as a simple and convenient process of producing large area thin films, favourable for photovoltaic application. However, there is competing undesirable homogeneous precipitation reaction and molecular level heterogeneous precipitation surface reaction that can affect the film quality. Degree of supersaturation of solution in CBD depends on which of these reactions reign supereme. pH of the reacting solution and ammonia concentration are two contrasting factors affecting both film thickness and supersaturation ratio. Hence, there is need to find correct pH and ammonia concentration that will put the solution at supersaturation ratio within the acceptable range for good guality film as well as the desired thickness at less deposition time. In this work, genetic algorithm (GA) in the frame multiobjective optimization (MO) was used to search for optimal pH, ammonia concentration and deposition time in order to minimize supersaturation ratio to the acceptable range for good quality film and maximize film thickness at the optimal deposition time. Multiobjective functions were formulated with constraint decision variables to evalutate fitness function for GA searching. Other genetic manupulative factors were fixed except population size which were varied from 30 to 90 in the step of 30 to search for near optimal solutions. The results show that population size of 90 gives best result with film thickness of 1.36?m and supersaturation ratio of 7.94 at deposition time 600s. The pH and ammonia concentration that evaluated these results are respectively 12.0 and 0.001142mol/cm3.
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