Vacuum-Processed Small Molecule Organic Photodetectors with Low Dark Current Density and Strong Response to Near-Infrared Wavelength

A near-infrared photodetector with optimized performance is reported using varied thickness (20, 40, 60, and 80 nm) of the active layer comprising chloroaluminium phthalocyanine (ClAlPc) and fullerene (C-70) at the ratio of 1:3, and TAPC:10% MoO(3)and BPhen as electron and hole blocking layers, respectively. The experimental results reveal that the photodetector with 80 nm thick active layer provides the best performance at the wavelength of 730 nm achieving a very low dark current density of 1.15 x 10(-9)A cm(-2)and an external quantum efficiency of 74.6% with a responsivity of 0.439 A W(-1)at -2 V bias. Additionally, the device exhibits a dramatic high detectivity of 4.14 x 10(13)cm Hz(1/2)W(-1)at 0 V bias. The device exhibits not only a large linear response over a wide optical power range (LDR of 173.0 dB), but also a broad frequency response (778.7 kHz) and rise/fall time of 2.13/0.77 mu s (based on trigger pulses at a frequency of 10 kHz) at the applied bias of -2 V. Based on the impedance spectroscopic study and the conventional characterization of electro-optical properties, the results demonstrate the superiority of this device over other small molecule-based near-infrared photodetectors.