How Gettering Affects the Temperature Sensitivity of the Implied Open Circuit Voltage of Multicrystalline Silicon Wafers

Abstract

The temperature sensitivity of the open circuit voltage of a solar cell is mainly driven by changes in the intrinsic carrier concentration, but also by the temperature dependence of the limiting recombination mechanisms in the cell. This paper investigates the influence of recombination through metallic impurities on the temperature sensitivity of multicrystalline silicon wafers. Spatially resolved temperature dependent analysis is performed to evaluate the temperature sensitivity of wafers from different brick positions before and after being subjected to phosphorus diffusion gettering. Local spatial analysis is performed on intra-grain areas, dislocation clusters and grain boundaries. Large variations in temperature sensitivity is observed across the wafers both before and after gettering. The spatially resolved γ parameter is found to change with gettering, indicating that the gettering process alters the balance between different recombination mechanisms in the material. Features with low temperature sensitivity are observed across the wafers and correlated with dislocation clusters. The locations of these areas remain unchanged by the gettering process, suggesting that the cause for the low temperature sensitivity is not removed. Gettering is observed to have a complex effect on the temperature sensitivity of the dislocation clusters depending on the wafer position in the brick, with dislocations from the top wafer exhibiting lowest temperature sensitivity both before and after gettering.