High detectivity squaraine-based near infrared photodetector with nA/cm[sup 2] dark current

We demonstrate an organic photodetector showing high detectivity (3.4×1012 Hz0.5 cm/W) at a wavelength of 700 nm, based on squaraine/phenyl-C61-butyric-acid-methyl-ester bulk-heterojunction active material. This result is achieved by suppressing the device dark currents while simultaneously preserving its external quantum efficiency, as high as 15% at 700 nm. To this aim, a thin cross-linked film based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] is exploited to suppress electron injection from the device anode into the organic blend, thus reducing the dark currents by a factor of 30, to the extremely low value of 2 nA/cm2. Also, the detector bandwidth ( ∼ 1 MHz) is unaffected by the introduction of a blocking layer