Improvement of near-infrared diffuse reflectance of silver back reflectors through Ag2O formation by a UV-ozone exposure process

Abstract

We report on the fabrication and analysis of highly optically reflective textured stacks consisting of silver oxide (Ag2O) coated silver for application as scattering back reflectors in thin-film solar cells. Thin Ag2O layers have been formed on textured silver back reflectors by using a UV-ozone (UVO) exposure technique, and during this formation, the stacks display improvement in their diffuse reflectance, particularly in the near infrared (NIR) spectral region. The silver oxide formed is composed of densely packed small grains with sizes from 20nm to 50nm, and their formation measurably increases the roughness of the silver reflector. The optimized silver reflector showed a ~ 6% increase in diffuse reflectance in the spectral range from 800nm to 1100nm while maintaining excellent total reflectance (over 95%). As a result, a high haze value (~ 98%) in the NIR region was achieved using these stacks. The stacks were tested as the back reflector in microcrystalline silicon solar cells. Due to the improved optical properties of the back reflector, a higher external quantum efficiency in the NIR region was obtained, and thus an increased short current density (from 22.3mA/cm2 to 23.6mA/cm2). It is also worth noting that the open circuit voltage was unchanged (0.529V) while the fill factor also increased (from 66.3% to 72.3%).