Atomic-level chemical reaction promoting external quantum efficiency of organic photomultiplication photodetector exceeding 10 8 % for weak-light detection

• Published in: Science bulletin Vol. 68; no. 9; p. 928
• Main Authors: Shi, Linlin, Zhu, Yizhi, Li, Guohui, Ji, Ting, Wang, Wenyan, Zhang, Ye, Wu, Yukun, Hao, Yuying, Wang, Kaiying, Yuan, Jun, Zou, Yingping, Ong, Beng S, Zhu, Furong, Cui, Yanxia
• Format: Journal Article
• Language: English
• Published: Netherlands 15.05.2023
• Subjects: Interfacial; Weak-light detection; Atomic layer deposition; AlO; Organic photodetectors; Photomultiplication
• ISSN: 2095-9281

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 Al O by the 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 Al O 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 forwardly-biased PM-OPD with Al O treatment reaches a remarkable level of 2.5 nW cm , while that of the reversely-biased control is 25 times inferior. Meanwhile, the PM-OPD yields a record high EQE and responsivity of 4.31 × 10 % and 1.85 × 10 A W , respectively, outperforming all other polymer-based PM-OPDs.