Improved silicon solar cells by tuning angular response to solar trajectory
Martin A. Green, Zibo Zhou
Abstract
Silicon solar cell costs are reducing dramatically with these cells now providing the majority of new electricity generation capacity worldwide. Cost reduction has been via economies of scale and steadily increasing sunlight energy conversion efficiency. The best experimental cells at 27.4% efficiency approach the 29.4% figure almost universally regarded as the limit on silicon cell performance. Here we show that assumptions in deducing this limit are too restrictive, since failing to incorporate sunlight directionality. Furthermore, we show how this directionality and the cell’s angular response can be quantified compatibly, using projections of angular dependencies of both onto the solar module plane. Even simple schemes for exploiting directionality, including installing solar modules facing the equator at near-latitude tilt, increase theoretical limiting efficiency above 29.4%. Highest gains are for cells designed for sunlight tracking systems, including common 1-axis trackers, with such cells having theoretical efficiency limits > 30%. In this work, we provide a strategy for ongoing improvements in commercial cell efficiency over this decade, additionally lowering cost via reduced cell thickness. The efficiency of silicon solar cells has been regarded as theoretically limited to 29.4%. Here, the authors show that the sunlight directionality and the cell’s angular response can be quantified compatibly; and with 1-axis sunlight trackers, they demonstrate an efficiency limit of over 30%.