Atomic-level Chemical Reaction Promoting External Quantum Efficiency of Organic Photodetector Exceeding 10^8% for Weak-Light Detection

Abstract Low-cost, solution-processed photomultiplication organic photodetectors (PM-OPDs) with external quantum efficiency (EQE) above unity have attracted enormous attention. However, their weak-light detection is unpleasant because the anode Ohmic contact causes exacerbation in dark current. Here, we introduce atomic-level chemical reaction in PM-OPDs which can simultaneously suppress dark current and increase EQE via depositing a 0.8 nm thick Al2O3 by atomic layer deposition. Suppression in dark current mainly originates from the built-in anode Schottky junction as a result of work function decrease of hole-transporting layer of which the chemical groups can react chemically with the bottom surface of Al2O3 layer at the atomic-level. Such strategy of suppressing dark current is not adverse to charge injection under illumination; instead, responsivity enhancement is realized because charge injection can shift from cathode to anode, of which the neighborhood possesses increased photogenerated carriers. Consequently, weak-light detection limit of the Al2O3 treated PM-OPD reaches a remarkable level of 2.5 nW/cm2, while that of the control is 25 times inferior. Meanwhile, the PM-OPD yields a record high EQE and responsivity of 4.31×108% and 1.85×106 A/W, respectively, outperforming all other polymer-based PM-OPDs.