The effect of rapid thermal annealing on the performance of CIGS cells with an ITO layer

Rapid thermal annealing studies were conducted on SS/Mo/CIGS/CdS/ITO/Ag devices as a function of anneal time in dry N₂ in the temperature range 50 to 200°C, as well as in humidified N₂ (85% RH) at 85°C. Interestingly, dry N₂ annealing produced an enhancement in cell performance for low thermal budget, predominantly due to increased J_SC, and to a lesser extent higher V_OC. As examples, CIGS cell efficiency increased by 1.8±0.8% after annealing at 50°C for 300s and 2.0±2.3% when annealed at 100°C for 600s. At higher anneal temperature or longer time the cell performance deteriorated with significant decrease in FF and V_OC. The results for the 85% RH at 85°C anneals were similar to the dry anneal studies but with less dramatic changes. Cell performance results after dark annealing indicate light-soaking effects induced by the lamp are not important at these relatively short anneal times. Measurement of quantum efficiency for the annealed samples supports the assumption that the buffer layer/absorber interface degrades at a relatively low temperature and that ITO degradation takes place at higher thermal budgets.