Printed organic thin-film transistors (OTFTs) are highly promising for flexible electronic applications due to their ability to be processed at low temperatures and their inherent flexibility. The advancement of these devices is significantly propelled by high-mobility organic semiconductors such as IDT-BT, which exhibit mobility on par with amorphous silicon. However, a persistent challenge is the degradation caused by water trapping in voids within the polymer matrix. In this study, we have fabricated printed OTFTs by incorporating additives into IDT-BT to effectively eliminate these voids, thereby enhancing environmental stability. Additionally, we have elucidated the physical mechanisms of environmental degradation by examining device performance under various environmental conditions and temperatures. These insights will facilitate the integration of printed OTFTs into flexible backplanes and circuits, thereby advancing the development of sophisticated flexible electronic systems.