Influence of PEIE interlayer on detectivity of red-light sensitive organic non-fullerene photodetectors with reverse structure

In this work we analyse an influence of 80% ethoxylated polyethyleneimine (PEIE) interlayer modifying the ITO electrode work function on the detectivity and time response of the red-light sensitive photodetectors based on donor-acceptor copolymer HFQx-T (where HFQx stands for hexafluoroquinoxaline acceptor units, and T for benzodithiophene derivative donor blocks) blended with acceptor ITIC (with indacenodithieno[3,2-b]thiophene as central donor unit and 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile as acceptor end groups). Modification of ITO electrode by PEIE interlayer allows to construct the photodiode with reversed structure which results in low dark current and high detectivity of the photodetector. The 3.5 nm thick PEIE interlayer causes strong reduction of the dark current in comparison to the dark current measured in classical photodiode structure; this allowed to obtain remarkably high detectivity, exceeding 2 × 1013 Jones. However, a presence of the PEIE interlayer has significantly lengthen the photodiode time response. We demonstrate that when designing the photodiodes with reversed structure, one should consider compromise between the required detectivity and the time response of the photodetector.