Abstract
GaAs nanowires (NWs) offer the possibility of decoupling light absorption from charge transport for high-performance photovoltaic (PV) devices. However, it is still an open question as to whether these devices can exceed the Shockley-Queisser efficiency limit for single-junction PV. In this work, single standing GaAs-based nanowire solar cells in both radial and vertical junction configurations is analyzed and compared to a planar thin-film design. By using a self-consistent, electrical-optically coupled 3D simulator, we show the design principles for nanowire and planar solar cells are significantly different; nanowire solar cells are vulnerable to surface and contact recombination, while planar solar cells suffer significant losses due to imperfect backside mirror reflection. Overall, the ultimate efficiency of the GaAs nanowire solar cell with radial and vertical junction is not expected to exceed that of the thin-film design, with both staying below the Shockley-Queisser limit.
Highlights
It is commonly understood that with the advent of low-cost, moderate efficiency photovoltaics, the long-term future of photovoltaics, sometimes called the ‘third generation,’ would combine low costs with substantially higher efficiencies [1]
For GaAsbased single-junction photovoltaics, the SQ limit is at 33.5% [4], and the highest efficiency obtained today is at 28.8% under 1-Sun with a thin-film design [5, 6]
We focus on this specific nanowire geometry and compare its radial and vertical junction configurations with thin-film design
Summary
It is commonly understood that with the advent of low-cost, moderate efficiency photovoltaics, the long-term future of photovoltaics, sometimes called the ‘third generation,’ would combine low costs with substantially higher efficiencies [1]. Nanowire solar cells can potentially satisfy both requirements and, as a result, are emerging as one of the most promising possibilities. Nanowire array solar cells have reached an efficiency of 13.8% [2]. The experimentally obtained efficiencies so far are still well below the ShockleyQueisser (SQ) limit—the ultimate theoretical efficiency limit for solar cells [3]. There is still a lot of room for improvement, and nanowire array solar cells offer one possible approach. Since a single GaAs-based nanowire solar cell was recently reported to have an apparent solar conversion efficiency of 40% [7], there is an open question as to whether performance at this level could extend to large-area arrays
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