Development and understanding of high efficiency screen printed concentrator silicon solar cells

Concentrator cells have the potential for reducing the usage of semiconductor material while producing high efficiency and more power density. Silicon solar cells now provide a unique opportunity for low-cost concentrator systems that are suitable for low to medium (2~20×) concentration because cell technology and screen printed contacts have improved considerably. New screen printing pastes, which give higher aspect ratio and good ohmic contacts to high sheet emitters, can now lead to high efficiency at low to medium concentration. In this paper, we report on the understanding and development of screen-printed concentrator solar cells which can meet the cost and efficiency targets for grid parity. Computer modeling was performed first to show that, under 10% metal coverage, it is possible for screen-printed cells to have series resistance that is low enough (<;0.286 Ω-cm²) to maintain significant efficiency at low to medium concentrations. This was validated by design and fabrication of 40.56cm² screen-printed cells using an industrial feasible process that achieved 17.2% efficiency at 20 suns and 18.8% peak efficiency at ~6 suns, which is the best screen printed Si cell efficiency reported in the literature in this concentration range. Model calculations show that ~20% efficient cells can be achieved at 5-12× with finer grid lines and improved contact resistance.