Evolution of LeTID defects in industrial multi-crystalline silicon wafers under laser illumination - Dependency of wafer position in brick and temperature

Abstract

In the past few years, a hot topic in both research and industrialization of p-type multi-crystalline silicon (mc-Si) solar cells is to investigate the mechanism, measurement and mitigation of the light- and elevated temperature-induced degradation (LeTID), which has been found to be a bulk-sensitive degradation behavior and is dependent on the degradation condition. In this paper, we study the influence of silicon bulk property on LeTID from five representative positions along a relative low resistivity (0.82–1.33 Ω cm) p-type mc-Si brick. The evolution of degradation and regeneration under different laser illumination conditions are investigated. Identical defect capture cross section ratio k values of ~35 at mid-gap along the brick height are found. For the first time, the activation energy for degradation (Ea,deg) and regeneration (Ea,reg) along the brick are studied, which shows Ea,deg = Ea,reg and a tendency of larger values towards the brick bottom. These results indicate that the LeTID in the whole brick might be induced by a single defect and thus mitigated in a single manner. Besides, a laser illumination of 45 kW/m2 at 142 °C for 100 s is able to induce over 90% degradation for all wafers, which could be used as a universal and fast LeTID test condition.