Inserting A Low -Refractive -Index Dielectric Rear Reflector Into Perc Cells: Challenges And Opportunities

One of the simplest and most effective ways to reduce the operating temperature of photovoltaic systems in the field is to reflect unusable, "sub-bandgap" light with energies below the cell absorber's bandgap energy. In this work, low refractive index Si02 nanoparticle films inserted between c-Si wafers and metal electrodes significantly increase the reflectance of sub-bandgap light in fabricated test structures. These films are then integrated into the standard PERC fabrication sequence, revealing that the reflection benefits remains after some processing steps but are lost in certain conditions. The Si02 nanoparticle films are easily ablated during laser contact opening, but are undesirably etched during post-laser cleaning. After Al metallization, the fully fabricated devices show enhanced subbandgap reflection when annealed at moderate temperatures, but energy-dispersive x-ray spectroscopy shows that hightemperature firing causes unwanted Al penetration into the Si02 nanoparticle film, compromising reflection.