Triple-junction InGaP/GaAs/Ge solar cells integrated with polymethyl methacrylate subwavelength structure

GaAs-based triple-junction tandem solar cells incorporating an antireflection coating (ARC) consisting of a subwavelength structure (SWS) and bilayer thin films are reported. A high aspect ratio SWS was realized on polymethyl methacrylate (PMMA) using a two-step etched silicon template and a stamping method. The fabricated PMMA SWS consisting of a two-dimensional array of nanoscale needles with a period of 300 nm and an aspect ratio exceeding 2.3 exhibited significantly improved optical performance. The average reflectance of the PMMA SWS was reduced from 7.1 to 4.4% as compared to that of the bare PMMA film, which resulted in an improvement of the transmittance from 90.7 to 92.9% in the wavelength range between 300 and 1700 nm. By integrating the PMMA SWS together with a TiO2/Al2O3 bilayer AR coating onto the top of an InGaP/GaAs/Ge triple-junction solar cell, the surface reflection of the solar cell could be minimized. The integrated PMMA SWS on the bilayer thin film ARC enhanced the power-conversion efficiency (η) of the triple-junction solar cell from 30.2 to 31.6% and from 37.8 to 40.8% under 1 and 157 sun condition, respectively.