Nanophotonic engineering shows great potential for photovoltaics: the record conversion efficiencies of nanowire solar cells are increasing rapidly1,2 and the record open-circuit voltages are becoming comparable to the records for planar equivalents3,4. Furthermore, it has been suggested that certain nanophotonic effects can reduce costs and increase efficiencies with respect to planar solar cells5,6. These effects are particularly pronounced in single-nanowire devices, where two out of the three dimensions are subwavelength. Single-nanowire devices thus provide an ideal platform to study how nanophotonics affects photovoltaics7,8,9,10,11,12. However, for these devices the standard definition of power conversion efficiency no longer applies, because the nanowire can absorb light from an area much larger than its own size6. Additionally, the thermodynamic limit on the photovoltage is unknown a priori and may be very different from that of a planar solar cell. This complicates the characterization and optimization of these devices. Here, we analyse an InP single-nanowire solar cell using intrinsic metrics to place its performance on an absolute thermodynamic scale and pinpoint performance loss mechanisms. To determine these metrics we have developed an integrating sphere microscopy set-up that enables simultaneous and spatially resolved quantitative absorption, internal quantum efficiency (IQE) and photoluminescence quantum yield (PLQY) measurements. For our record single-nanowire solar cell, we measure a photocurrent collection efficiency of >90% and an open-circuit voltage of 850 mV, which is 73% of the thermodynamic limit (1.16 V).
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We acknowledge A. Polman for the use of lab space and equipment and for a thorough reading of the manuscript, M. Seynen, H.-J. Boluijt and D. Verheijde for technical support and H.-J. Boluijt for the schematic in Fig. 1c. We would like to thank R. Van Veldhoven for maintaining the MOCVD system and M. Verheijen for the TEM measurements. We acknowledge Solliance for funding the TEM facility and the technical support from the NanoLab@TU/e cleanroom. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme ((FP/2007–2013)/ERC Grant Agreement No. 337328, ‘NanoEnabledPV’), the Dutch Technology Foundation STW (project 11826), which is part of the Netherlands Organization for Scientific Research (NWO), and the Dutch Ministry of Economic Affairs. This work is part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is part of The Netherlands Organization for Scientific Research (NWO).
The authors declare no competing financial interests.
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Mann, S., Oener, S., Cavalli, A. et al. Quantifying losses and thermodynamic limits in nanophotonic solar cells. Nature Nanotech 11, 1071–1075 (2016). https://doi.org/10.1038/nnano.2016.162
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