This study elucidates the thermal-induced bandgap broadening (TBB) phenomenon in copolymer organic semiconductors (OSCs). From the perspective of device physics, the diketopyrrolopyrrole-based copolymer was employed as the semiconductor layer to fabricate a back-to-back Schottky junction structure. Characterization through the analysis of I–V curves enables the qualitative exploration of the correlation between bandgap and temperature in copolymer OSCs. Then, technology computer-aided design was utilized to explore the influence of thermal-induced bandgap broadening on the back-to-back Schottky I–V curves. Subsequently, the variable temperature UV-VIS-NIR absorption spectra of the copolymer OSCs were analyzed, providing quantitative evidence of the thermal-induced bandgap broadening phenomenon and confirming its recoverability. Through the research of the Schottky junction and absorption spectra, we verified the consistency of the TBB phenomenon in both the electrical and optical bandgaps. From the scanning electron microscope images of the copolymer OSC films, it is found that the thermal-induced bandgap broadening phenomenon is mainly caused by thermal expansion and increased disorder of copolymer molecules. This study highlights a physical phenomenon of copolymer OSCs that is different from most inorganic semiconductors, and such insight offers a theoretical perspective for the application and thermal stability investigation of copolymer devices under high temperature conditions.

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