Quantifying losses and thermodynamics limits in nanophotonic solar cells

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. Singlenanowire devices thus provide an ideal platform to study how nanophotonics affects photovoltaics7–12. 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)

Controlling crystallization to imprint nanophotonic structures into halide perovskites using soft lithography

Halide perovskites have recently gained widespread attention for their high efficiencies in photovoltaics, and they have also been studied for applications in light emission. Both of these fields can benefit from nanophotonic patterning. Here, by controlling the crystallization of the perovskite film in contact with a nanotextured silicone polymer stamp, nanostructures are reproduced in the perovskite. Soft lithography techniques such as this imprinting are particularly useful for halide perovskites, which are incompatible with the aqueous solutions and plasmas used in conventional patterning processes. Additionally, soft lithography can pattern over defects and avoids damaging the master. By extending nanoscale soft lithography to halide perovskites, new opportunities arise in merging nanophotonics with these remarkable materials