The influence of Al-doped ZnO (AZO) thin films degraded under high temperature and damp heat on the performance deterioration of Cu(In,Ga)$Se_2$ (CIGS) solar cells was investigated. CIGS solar cells with AZO/CdS/CIGS/Mo structure were prepared on glass substrate and exposed to high temperature ($85^{circ}C$) and damp heat ($85^{circ}C$/85% RH) for 1000 h. As-prepared CIGS solar cells had 64.91% in fill factor (FF) and 12.04% in conversion efficiency. After exposed to high temperature, CIGS solar cell had 59.14% in FF and 9.78% in efficiency, while after exposed to damp heat, it had 54.00% in FF and 8.78% in efficiency. AZO thin films in the deteriorated CIGS solar cells showed increases in resistivity up to 3.1 times and 4.4 times compared to their initial resistivity after 1000 h of high temperature and damp heat exposure, respectively. These results can be explained by the decreases in carrier concentration and mobility due to diffusion or adsorption of oxygen and moisture in AZO thin films. It can be inferred that decreases in FF and conversion efficiency were caused by an increase in series resistance, which resulted from an increase in resistivity of AZO thin films degraded under high temperature and damp heat.