22.6% Efficient Solar Cells with Polysilicon Passivating Contacts on n-type Solar-Grade Wafers

Czochralski (Cz)-grown upgraded metallurgical-grade (UMG) silicon wafers degrade significantly during high-temperature processes, eroding their appeal as a low-cost alternative to conventional electronic-grade silicon wafers. However, the thermal degradation in UMG wafers can be delayed by utilizing a prefabrication annealing step. Based on this, a high-efficiency solar-cell process is modified by selecting a single-boron diffusion step and applying phosphorus-doped polycrystalline films as electron-selective contacts with excellent impurity-gettering properties to minimize the thermal budget. The application of this modified high-efficiency solar-cell process to n-type UMG-Cz wafers results in a solar cell with a conversion efficiency of 22.6% on a cell area of 2 × 2 cm².