Optimization of Photon and Electron Collection Efficiencies in Silicon Solar Microcells for Use in Concentration-Based Photovoltaic Systems

Ultrathin silicon solar microcells (mu-cells) afford a means to reduce semiconductor material consumption and can be integrated with concentration optics to improve their power density. A mu-cell design is described that optimizes electron and photon collection with enhanced efficiency for solar concentration applications. An interdigitated back contact (IBC) design improves carrier collection partially due to larger contact coverage while further enabling optimization of the mu-cell front surface. To do so, a silicon nitride antireflection thin film coating is utilized to enhance photon absorption and improve surface passivation. Performance of IBC mu-cells is compared to an optimized top contact design and improves mu-cell conversion efficiencies from 9.9 to 13.7%. Improvements at 1 Sun are amplified under concentration and increase power densities at 20 Suns to 346 from 192 mW cm(-2) due to minimized series resistance. Benefits afforded by IBC mu-cells are exemplified following their integration into a dual concentrator system, affording photon collection capacities for direct and diffuse irradiance. A traditional lens concentrates direct light while a luminescent solar concentrator (LSC) collects diffuse photons otherwise not utilized by passive optics. Addition of the LSC increases maximum power densities on clear and cloudy days, providing concentration for the latter and further increasing the power density.