Suppression of Significant Dark Current in Organic Photodetectors through Side Chain Fluorination of Conjugated Polymers
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The dark current density (Jdark) is a critical aspect affecting signal-to-noise ratio, linear dynamic range, and detection sensitivity of organic photo-detectors (OPDs).1 Despite its importance, Jdark in OPDs produced through liquid processes is poorly understood and challenging to control.2-4 This study investigates the effect of adding fluorine atoms to conjugated polymers (CPs) on OPD performance. OPDs made with fluoro-alkylated CPs showed a high external quantum efficiency (78%) and Jdark suppression (≈3.73 x 10-10 A·cm-2, -2V) by 100 times. The fluoro-alkylation of CPs leads to regular molecular structures, reducing trap density and energy disorder, resulting in effective Jdark suppression and improved charge carrier mobility. These OPDs also exhibit high D* (≈3.39 x 1013 cm·Hz1/2·W-1, -2 V) and appropriate response speed (f-3db≈56.31 kHz). The study also demonstrates a photoplethysmography (PPG) sensor using fluoro-alkylated CPs. (1) Sol. RRL, 4, 2000139 (2020). (2) Adv. Funct. Mater., 29, 1805058 (2019). (3) Adv. Mater., 28, 4766 (2016). (4) Adv. Funct. Mater., 30, 2001402 (2020).