Coupling of light scattered by nanoparticles into waveguide modes in quantum-well solar cells

Abstract

We describe experimental and theoretical analysis of coupling of light scattered by metal or dielectric nanoparticles into waveguide modes of InP/InGaAsP quantum-well solar cells. The integration of metal or dielectric nanoparticles above the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material. Photocurrent response spectra yield clear evidence of scattering of photons into the multiple-quantum-well waveguide structure, and consequently increased photocurrent generation, at wavelengths between the band gaps of the barrier and quantum-well layers. With minimal optimization, a short-circuit current density increase of 12.9% and 7.3% and power conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively. A theoretical approach for calculating the optical coupling is described, and the resulting analysis suggests that extremely high coupling efficiency can be attained in appropriately designed structures.