PLASMON-ENHANCED ABSORPTION AND PHOTOCURRENT IN ULTRATHIN GaAs SOLAR CELLS WITH METALLIC NANOSTRUCTURES

Metallic nanostructures can excite surface plasmons and can dramatically increase the optical path length in thin active photovoltaic layers to enhance overall photoabsorption. This effect has potential for cost and weight reduction with thinned layers and also for efficiency enhancement associated with increased carrier excitation level in the absorber layer. We have observed short-circuit current and efficiency enhancements under AM1.5G solar spectrum for GaAs cells with dense arrays of Ag nanoparticles deposited through porous alumina membrane masks, relative to reference GaAs cells with no metal nanoparticle array. This photocurrent enhancement is attributed to the scattering effects of metal nanoparticles for light incident into photovoltaic layers. A simple optical model representing metal nanoparticle surface plasmon resonances and multi-angle scattering has been developed and well explains the spectral behavior of the experimental photocurrent enhancement. A novel ultrathin GaAs cell structure with a metallic back layer has been also developed with a bonding and layer transfer technique. This waveguide-like GaAs cell showed significant enhancements in short-circuit current density and efficiency relative to reference GaAs cells with an absorbing GaAs back layer due to a Fabry-Perot resonance in the air/semiconductor/meta heterostructure.