Perfect absorption in nanotextured thin films via Anderson-localized photon modes

The enhancement of light absorption in absorber layers is crucial in a number of applications, including photovoltaics(1) and thermoelectrics. The efficient use of natural resources and physical constraints such as limited charge extraction in photovoltaic devices require thin but efficient absorbers. Among the many different strategies used(2-7), light diffraction(8) and light localization(9,10) at randomly nanotextured interfaces have been proposed to improve absorption. Although already exploited in commercial devices, the enhancement mechanism for devices with nanotextured interfaces is still subject to debate. Using coherent two-dimensional nanoscopy and coherent light scattering, we demonstrate the existence of localized photonic states in nanotextured amorphous silicon layers as used in commercial thin-film solar cells. Resonant absorption in these states accounts for the enhanced absorption in the long-wavelength cutoff region. Our observations establish that Anderson localization-that is, strong localization-is a highly efficient resonant absorption enhancement mechanism offering interesting opportunities for the design of efficient future absorber layers.