Highly Sensitive UV–Vis‐to‐Near‐Infrared Organic Photodetectors Employing ZnO: Polyethylenimine Ethoxylated Composite as Hole‐Blocking Layer

Abstract

Significantly suppressed leakage current and reduced shot noise in organic photodetectors (OPDs) are achieved by employing charge blocking layers, which have led to tremendous advances in highly sensitive devices with photoresponse covering from the ultraviolet to near‐infrared regions. However, trap‐assisted charge carrier injection through tunneling can significantly contribute to the sources of leakage current upon the use of charge blocking layers. Herein, it is shown that leakage current in organic photodetectors can be effectively reduced to an intrinsic lower limit by using a composite hole blocking layer (HBL) that consists of zinc oxide (ZnO) blended with different weight concentration of polymer polyethylenimine ethoxylated (PEIE). The best device shows an ultralow dark current density down to 0.18 nA cm−2, which translates to high specific detectivity (D*) over 1 × 1013 Jones in broad response range from 340 to 1100 nm (with peak value of 4.2 × 1013 Jones at 940 nm and 3.5 × 1013 Jones at 1050 nm), approaching to the intrinsic dark current‐limited detectivity value. It is found that the incorporated N atoms fill the deficient site of oxygen in ZnO, thus giving rise to the reduced proportion of emission via defects.

Highly Efficient Ternary Near-Infrared Organic Photodetectors for Biometric Monitoring

“…Photodetection techniques rely on the ability to convert optical signals into electrical signals for various applications, including image sensing, optical communication, and medicine . Because of their low cost, light weight, flexibility, and amenability to rapid roll-to-roll printing, organic PDs (OPDs) have received much attention for their potential advantages over conventional PDs based on silicon and other inorganic counterparts. − Typically, solution-processed OPDs have been fabricated using blends of donors and acceptors to form bulk-heterojunction (BHJ) active layers. , Benefiting from the successful use of non-fullerene acceptors (NFAs) in organic photovoltaics (OPVs), the device performance of OPDs has progressed tremendously in recent years . Nevertheless, some key issues have thwarted the commercialization of OPDs, including how to suppress the dark current under reverse bias for high detectability and how to realize an ultrafast response and minimize injection of charge carriers.…”

Quantification of an effective charge injection barrier in non-fullerene-based organic photodetectors

“…Therefore, there appears to be a consensus that the dark current in organic photodetectors mainly originates from the charge injection across the electrode/organic interface under reverse bias, while contribution due to bulk thermal generation of carriers becomes negligible when the bandgap of the semiconductor is larger than 1.0 eV. 9,10,[12][13][14] Given that charge injection is recognized to be the dominant source of dark current in OPDs as mentioned above, its careful evaluation is highly urgent. However, this goal is not satisfactorily achieved because the factors that affect the charge injection are very complicated by the ill-defined nature of organic materials and the organic/electrode interface.…”

Suppressed Trap Density Leads to Versatile p‐i‐n Heterojunction Photodiode with Enhanced Photovoltaic/Photodetection Dual‐Function

“…For instance, uncontrolled J dark aggravates shot noise ($${S_{{\rm{shot}}}} = \sqrt {2e{I_{{\rm{dark}}}}\Delta f} $$), which is detrimental to the detectivity of OPDs. [ 24,25 ] On the other hand, the resultant large non‐radiative recombination and energetic disorder have been identified as the determining mechanisms for the loss of open‐circuit voltage ( V OC ) in OPV devices. [ 26 ]…”

“…), which is detrimental to the detectivity of OPDs. [24,25] On the other hand, the resultant large non-radiative recombination and energetic disorder have been identified as the determining mechanisms for the loss of open-circuit voltage (V OC ) in OPV devices. [26] To address these issues, considerable optimization strategies have been proposed to improve the solid-state molecular arrangement of OPV and OPDs.…”