Optoelectronic Enhancement of Ultrathin CuIn1-xGaxSe2 Solar Cells by Nanophotonic Contacts

Abstract

CuIn1–xGaxSe2 (CIGSe) solar cells have achieved record efficiency values as high as 22.6% for small areas, with module efficiency values of 16.5%. However, for economic viability these values must be achieved with reduced material consumption (especially indium), which requires reducing the CIGSe absorber thickness from 2000–3000 nm to below 500 nm. Soft-imprinted SiOx nanoparticles (NPs) beneath a conformal CIGSe layer enable this thickness reduction. Optically, they enhance the absorption of light through Fabry–Pérot and waveguided resonances within the CIGSe layer, preventing current loss. For CIGSe solar cells on ITO with an absorber thickness of only 390 nm and a nanophotonic contact the current density (Jsc) increases from 25.7 to 32.1 mA cm−2. At the same time, the nanopatterned contact reduces the back barrier, leading to an increased open-circuit voltage (518 to 558 mV) and fill factor (50.7% to 55.2%). Combined, these effects increase the efficiency value from 6.8% to 10.0% for this initial demonstration. With the addition of an antireflection coating, the champion NP-enhanced cell achieves a Jsc of 34.0 mA cm−2, corresponding to 93% of the Jsc achieved by the thick world-record cell. This result shows that optoelectronic nanopatterning provides a path to high efficiency cells with reduced materials consumption.