Enabling highly conductive charged oxide inversion layers through hot corona discharge

Silicon solar cell manufacturing is dominated by cell architectures that rely on a high-temperature energy-intensive diffusion process to introduce dopants. Such doped layers lead to substantial Auger recombination losses. Charged oxide inversion layer (COIL) solar cells eliminate the need for high-temperature diffusion and highly doped surface layers by incorporating charge in a surface dielectric to form an inversion layer emitter beneath the semiconductor-dielectric interface. The success of the COIL design hinges on achieving a sufficiently high dielectric charge to produce highly conductive inversion-layer emitters. In this work, we develop a new “hot-corona discharge” technique to facilitate the charge drive-in via a process integrating corona charging and thermal annealing into a single step. We show the process is effective in creating an n-type inversion layer on p-type silicon wafers, yielding increases in carrier lifetime and reductions in emitter sheet resistance. The temperature (330–430 °C) and time (30–1020 s) dependence of this new hot-corona approach is studied, demonstrating careful control over charge density. By optimising the process against temperature and ion drive-in cycles, we achieve the highest positive charge concentration reported on a SiO2/Si interface of >4.0 × 1013 q/cm2. With the ability to incorporate such high charge density, a low sheet resistance and highly conductive inversion layer can be formed. This represents a significant step forward in the attempt to replace the diffused emitter technology with a low-temperature alternative, enabling high-efficiency inversion-layer solar cells with reduced thermal budget and intrinsic losses.