Rational Molecular Design of π-Extended Thiazolothiazole for High-Performance UV-OPDs Seamlessly Integrated with CMOS

Abstract

Vacuum-deposited organic photodiodes (OPDs) offer unique advantages-including narrowband selectivity and compatibility with standard fabrication processes-but achieving ultraviolet (UV) selectivity in such devices remains a key challenge. This is due to the need to reconcile two competing design requirements: 1) strong pi-pi stacking for efficient charge transport, and 2) limited pi-conjugation to retain a wide bandgap suitable for UV absorption and vacuum deposition. Here, we report a molecular design strategy for UV-selective OPDs based on thiazolothiazole (Tz)-based small molecules with tailored backbone planarity and conjugation length. The resulting vacuum-deposited active layers simultaneously exhibit wide bandgaps and robust pi-pi interactions. The optimized devices achieve outstanding UV selectivity (full-width at half-maximum: 60 nm), high specific detectivity (1.06 x 1012 Jones), and fast dynamic response (cutoff frequency of 50,100 Hz)-representing the highest performance for vacuum-deposited UV-OPDs reported to date. Furthermore, it is demonstrated the seamless integration of these semi-transparent OPDs with complementary metal-oxide-semiconductor (CMOS) image sensors (CIS), underscoring their potential for multifunctional imaging applications. The findings provide key molecular insights for advancing UV-selective organic photodetectors.