Large photoresponse from a small molecule: Application in photodetector and pseudo-transistor

The observation of large photoresponsivity in a π-conjugated small organic molecule, viz., N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) and consequently, fabrication of organic photodetector with single layer of PTCDI-C8 is reported. The same device, without any actual gate terminal, can also be used to obtain field-effect transistor (FET) characteristics by exploiting the photoresponse properties of the material. Photo-illumination on the active material which ensured an induced channel by the photo generated charge carriers, resembled as the pseudo gate electrode. The simple lateral structure with gold (Au) as source and drain electrodes and vacuum deposited thin film of PTCDI-C8 as the active layer produced high-performance photodetector and transistor behavior, showing pseudo-output and transfer curves with an on/off ratio of 4 × 102. The two terminal organic devices exhibited photoresponsivity value ca. 50 mA/W, external quantum efficiency ∼40%, reproducible and reversible photo-switching behavior with photo to dark current ratio ca. 200 and a switching time <10 ms. Modulation and tuning of the device's performance were done by controlling the number of photo generated carriers. The multifunctional ability, such as, photosensing, photoswitching, and signal amplification realized in a single unit opens up immense possibilities for integrated device applications in large-scale and low-cost plastic optoelectronic devices.

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