A low-cost and novel method for fabricating bifacial solar cells
In this work we proposed and demonstrated a novel and very cost effective method to fabricate bifacial solar cells with conventional structure. Bifacial cells collect sunlight from both faces, and hence have an obvious advantage over monofacial cells by occupying the same physical area and converting solar energy to electricity more efficiently. Despite this fact, bifacial cells are not that popular simply because of the costs associated with them. These costs are related to both manufacturing of the actual cells and integration of modules/solar panels. The cost of manufacturing is higher than regular commodity cells because the number of processing steps for fabrication is higher than their monofacial counterparts. The main reasons for that is a necessity of some kind of lithography step and/or alignment to make the grid pattern on both sides separately. Also metallization has to be done on both sides separately, one at a time. The method proposed in this work gets rid of both of those limitations by use of a lithography/alignment-less method for patterning contact holes, and a low temperature metallization scheme used for both the front and rear surfaces to grow metal simultaneously. This technique is simple and cost effective enough to be potentially incorporated in a batch process in industry, thereby reducing the cost of manufacturing. In this thesis we have presented preliminary results from the cells (bifacial and monofacial) fabricated using the above technique with proposals for further improvements. The measurement data underscores the clear advantage in using bifacial cells over monofacial cells fabricated using this method, in terms of efficiency. This also demonstrates that this proposed method is a viable way to manufacture bifacial cells with lower cost and relative ease. We also fabricated and measured monofacial solar cells in order to study the beneficial effects of including buried contacts as a possible part of device structure. The study shows significant improvement in efficiency due to incorporation of deep trenches for metal contacts in device design.