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

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-Perot 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 (J(sc)) 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 J(sc) of 34.0 mA cm(-2), corresponding to 93% of the J(sc) achieved by the thick world-record cell. This result shows that optoelectronic nanopatterning provides a path to high efficiency cells with reduced materials consumption.