Inserting a Low-Refractive-Index Dielectric Rear Reflector into PERC Cells: Challenges and Opportunities: Preprint

One of the simplest and most effective ways to reduce the operating temperature of photovoltaic systemsin the field is to reflect unusable, 'sub-bandgap' lightwith energies below the cell absorber's bandgap energy. In this work, low-refractive index SiO2nanoparticle 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 intothestandard PERC fabrication sequence, revealing that thereflection benefits remains after some processing stepsbut are lost in certain conditions. The SiO2nanoparticle films are easily ablatedduring laser contact opening, but are undesirably etched during post-laser cleaning. After Al metallization, the fully fabricated devices show enhanced sub-bandgap reflection when annealed at moderate temperatures, but energy-dispersive x-ray spectroscopy showsthat high-temperature firing causes unwanted Al penetration into the SiO2nanoparticle film, compromising reflection.