• omnidirectional;
  • anti-reflection;
  • tailored-refractive-index;
  • photovoltaic devices;
  • solar cells


An optimized four-layer tailored- and low-refractive index anti-reflection (AR) coating on an inverted metamorphic (IMM) triple-junction solar cell device is demonstrated. Due to an excellent refractive index matching with the ambient air by using tailored- and low-refractive index nanoporous SiO2 layers and owing to a multiple-discrete-layer design of the AR coating optimized by a genetic algorithm, such a four-layer AR coating shows excellent broadband and omnidirectional AR characteristics and significantly enhances the omnidirectional photovoltaic performance of IMM solar cell devices. Comparing the photovoltaic performance of an IMM solar cell device with the four-layer AR coating and an IMM solar cell with the conventional SiO2/TiO2 double layer AR coating, the four-layer AR coating achieves an angle-of-incidence (AOI) averaged short-circuit current density, JSC, enhancement of 34.4%, whereas the conventional double layer AR coating only achieves an AOI-averaged JSC enhancement of 25.3%. The measured reflectance reduction and omnidirectional photovoltaic performance enhancement of the four-layer AR coating are to our knowledge, the largest ever reported in the literature of solar cell devices.