A novel room temperature contacting technique applied to silicon solar cells

Abstract

A novel room temperature technique for ohmic contact formation to silicon has been investigated for application in silicon solar cells. Point-contacting by Localised Dielectric Breakdown (PLDB) relies on localised high doping to ensure electric field based breakdown of a passivating dielectric layer occurs preferentially at the high doping regions. This technique has been applied to two different types of solar cell designs. The first design, a conventional n on p front emitter design, used PLDB to form a point contact array at the rear surface. Results show good performance for both contact recombination and contact resistivity at the rear contacts. A lower than expected pseudo fill factor is shown to be largely caused by recombination in apertured regions beyond the active cell area. Investigation of the robustness of the process by applying a larger than necessary voltage leads to two separate breakdown events, both characterised by a Weibull distribution of breakdown voltages. The voltage ranges for these events are found to be well separated, meaning a voltage processing window exists that ensures completion of the contact formation, without damaging the surface passivation of the dielectric layers. Finally, the PLDB process has been applied to an interdigitated back contact (IBC) solar cell design employing a full area emitter. The self-aligned nature of the process has several benefits for improved carrier collection and greatly simplified fabrication flow. Results indicate an ongoing issue with a leakage current to p-type doped regions that was unresolved. Simulation work, using a Quokka based simulation model, indicate the potential for this type of IBC design to improve performance over more conventional designs, providing the processing issues identified can be overcome. Suggestions for future work to determine the best design for implementing PLDB in an IBC are also discussed.