Thickness-dependent performance of a 2AC-CF₃Ph single-component donor–acceptor–donor UV organic photodiode

The development of efficient and stable ultraviolet (UV) organic photodiodes (OPDs) remains a key challenge in optoelectronic research. Herein, we report the design and characterization of a single-component donor–acceptor–donor (D-A-D) conjugated molecule, 10,10′-(2-(trifluoromethyl)-1,4-phenylene) bis(9,9-dimethyl-9,10-dihydroacridine), for UV photodetection. Density functional theory (DFT) calculations revealed balanced charge delocalization across donor and acceptor moieties, an energy gap of 3.01 eV, and a small singlet-triplet energy splitting (ΔEST ≈ 0.05 eV), favouring efficient charge transfer. The molecule exhibited strong UV absorption (200–330 nm), high photoluminescence quenching behaviour, and remarkable thermal stability with a decomposition onset above 297 °C. Device performance was strongly dependent on the active layer thickness. The OPD incorporating a 10 nm film achieved superior photoresponse characteristics, including a high photocurrent density (75.18 mA/cm2), responsivity (742.2 mA/W), detectivity (1.38 × 1012 Jones), and fast response times (Tr/Td = 1 s). In contrast, the 100 nm film showed lower responsivity and slower dynamics due to enhanced recombination from surface roughness. These findings highlight a promising single-component material for efficient, thermally stable UV photodetectors. This work demonstrates that precise thickness control can substantially enhance charge extraction and response speed in organic UV sensing applications.

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