Impact of agricultural atmospheric pollutants on the opto-electrical performance of CIGS solar cells

The reliability of CIGS solar systems in agricultural environments was investigated using an accelerated aging test. Both complete cells and representative stacks of selected layers and interfaces were exposed to humidity and temperature variations for 9 to 14 days with and without ammonium sulfate (NH₄)₂SO₄, an aerosol pollutant representative of agricultural activities. The performance evolution of complete cells was evaluated by J-V curves and EQE measurements. After 9 days, the presence of (NH₄)₂SO₄ led to a performance loss of 58%, significantly higher than the 37% loss observed without pollutants. Using computer calculations based on the two-diode model, it was possible to de-correlate some interactions between J-V parameters. The results of modeling suggested that the pollutant caused optical losses and conductivity loss of electrical contacts, presumably by corrosion. Sheet resistance and Hall effect measurements on the representative stacks of layers confirmed that the conductivity loss of ZnO:Al (AZO) after 14 days of aging strongly impacted the cell performance, this phenomenon being even more severe in the presence of (NH₄)₂SO₄. The conductivity of Mo remained significantly less affected by aging both with and without pollutants. The NiAlNi contacts after aging with (NH₄)₂SO₄ became so resistive that measurement was impossible. Corroborating modeling and experimental results, the drop in J_sc was attributed to the loss of the interference fringes in the AZO rather than to the loss of optical transmittance. Finally, aging without pollutants mostly impacted V_oc and R_sh due to the formation of shunt paths.