The objective of this study is to investigate the stability of the active layer of polymer solar cells from the effect of UV-visible light irradiation using different conditions with respect to time. The active layers were composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM), deposited on conductive glass substrates through spin coating. These samples are placed in a UV-visible light exposure chamber using different conditions (heat and water) over the specific periods of time. The samples are analyzed by UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy (FTIR) measurements. The results indicate that after continuous exposure to UV irradiation for 72 and 120h, the sample shows a significant decrease in absorption of the main peak. The sample shows around 25% loss in absorption (main peak) after 72h of irradiation. The FTIR results illustrate a progressive decrease in intensities of all typical absorption peaks owing to P3HT ring scission, side chain oxidation as well as degradation of the side groups of PCBM. [GRAPHICS] .