In this study, a diketopyrrolopyrrole (DPP)-based small molecule, 3,6-bis(5′-(2-octyldodecyl)-[2,2’-bithiophen]-5-yl)-2,5-dipropyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DBT-I), was synthesized via Stille coupling. The thin-film morphology, crystallinity, and organic field-effect transistor (OFET) performance of DBT-I were systematically investigated under various solution-processing techniques and solvent environments. Particular emphasis was placed on understanding the influence of processing conditions on film microstructure and their correlation with device performance. It was found that the appropriate combination of solvent, deposition method, and thermal treatment significantly enhances the crystallinity of the DBT-I thin films. Since the electrical properties are influenced by the chemical structure and morphology of the semiconductor, the obtained low-bandgap material was integrated into OFETs fabricated by solution-processing methodologies, such as spin coating and solution-shearing. The optimal performance in OFETs was achieved with the shear-coated DBT-I films, showcasing a mobility of 0.26 cm²V^–1s^–1and a current on–off ratio of 10⁶. The OFET performance correlated with morphology features such as crystallinity and grain size opens the possibility for a rational optimization of OFET characteristics.