The present disclosure relates to an additive for improving the light stability of a conjugated polymer, a method for preparing the same and an organic photovoltaic cell containing the same. Since the additive of the present disclosure improves the light stability of a conjugated polymer, it can be used for an organic photovoltaic (OPV) cell device and can also be usefully used for an organic optoelectronic device using a conductive polymer, such as an organic photodiode (OPD), an organic thin-film transistor (OTFT), an organic light-emitting diode (OLED), etc.