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.

Enhanced photomultiplication in filter-free organic photodetectors for red and NIR light sensing using minimal nonfullerene blends

“…[28][29][30] These devices incorporate minimal acceptor content in organic BHJ layers, acting as electron traps to enhance hole injection, known as the charge injection narrowing (CIN) effect. [31][32][33] For instance, Wang et al reported red-light PM-OPDs with an EQE of 53 500% using a 2.5 mm thick P3HT:PC 71 BM layer at a high À60 V bias. 34 Similarly, NIR PM-OPDs incorporating PTB7-Th achieved EQEs around 2000% at À50 V. 35 Suthar et al proposed a narrowband PM-OPD at low external biases through a pseudo bilayer structure comprising a photon-filtering layer and a PM layer.…”