Impact of copper back contact in CdTe solar cells: study of defects by temperture-dependent capacitance-voltage measurements

摘要

Copper diffusion from back contact creates semishallow and deep-level defects in n~+-CdS/p-CdTe solar cells. This study analyzes the impact of copper as a function of annealing temperatures during back contact formation. The observed defect levels, formed after copper diffusion, were identified by employing the temperature-dependent capacitance-voltage (C-V) characteristics at reverse bias in the dark. Theoretical background involving recombination centers, defect density and the role of impurity defects (copper-related defects) suggests that the temperature-dependent C-V profiling is a suitable technique to investigate the copper-related defects. Samples, annealed at 160℃ for 30min, show only one energy level, whereas samples annealed at 280℃ for 30min reveal two distinct deep levels. From the reported observations, the trap levels were identified as copper-related defects. Variation in annealing temperature can impact the defect formation process: substitutional impurities of copper (160℃) and deep levels (280℃).