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The effect of ultraviolet (UV)-light ozone exposure on phenyl-C61-butyric acid methyl ester (PC61BM) is studied using solid-state modification of the material. In this study, solution processed PCBM films that have been deposited and dried over glass were exposed to UV ozone at ambient temperature and pressure from 0 to 120 min. Core-level and valence-band photoelectron spectroscopy studies indicate that the UV-ozone-induced oxidation results in C-O-C bonds in PCBM and a change in the highest occupied molecular orbital level, respectively. The modification of PCBM with C-O-C binding was observed from 5 to 60 min, but further exposure, typically beyond 120 min, was found to degrade the material. A solubility study also showed an exposure time-dependant solubility change of the material, in solvents like toluene and acetone, where it indicates the change in the chemistry of the material that can be related to the C-O-C binding of the material by the exposure. The method is an easily implementable approach for flexibility on choice of solvents for PCBM, and it has implications on the processing and stability of the material.