계면 제어를 통한 빠른 응답속도를 지니는 광증폭형 유기 포토디텍터의 개발

Abstract

Organic photodetectors have emerged as promising optoelectronic devices due to their unique properties and wide-range applications. Unlike conventional inorganic photodetectors, organic photodetectors utilize organic semiconductors as a photoactive layer, offering advantages such as flexibility, lightweight, and compatibility with large-area and flexible substrates. This research aims to enhance the performance of organic photodetectors, specifically focusing on the photomultiplication (PM) type organic photo diodes (OPDs), which enables efficient detection of weak light signals without the need for pre-amplifier circuits. However, the response speed of PM-OPDs has been a critical limitation. In this study, I suggest the charge carrier trapping and accumulation process within the PM operating mechanism as a potential bottleneck for the response speed. To address this, I propose a novel device architecture incorporating a PM-inducing interlayer. Two different types of interlayers are incorporated: a core-shell quantum dot (QD) monolayer and an ionic crystal-based metal-halide perovskite QD monolayer. In Chapter 2, a core-shell QD monolayer is positioned between the photoactive layer and a metal electrode in a PM-OPD. This interlayer effectively suppresses dark current and facilitates photocurrent significantly reducing the time required for charge accumulation by rapidly capturing and trapping photo-generated electrons. The PM-OPD with the core-shell QD interlayer demonstrates high response speed and a high external quantum efficiency (EQE). I further demonstrate that the response speed of the PM-OPD is determined by the charge carrier trapping dynamics within the QD interlayer and therefore the response time of the PM-OPD can be effectively manipulated by controlling the charge trapping dynamics of the QD interlayer. In Chapter 3, I focus on an alternative approach using an ionic crystal-based metal-halide perovskite QD interlayer. Ion migration within these QDs induces PM, enabling high EQE, fast response, and an improvement in the EQE-bandwidth product. This performance was achieved at a low operating bias voltage of 3 V, which is comparable to the actual operation voltage of a commercial image sensor. I also confirmed the dynamics of ionic motion play a critical role in determining the response speed of the PM-OPD. This research not only identifies the bottleneck process in PM operation but also proposes novel device architectures to minimize the time required for charge carrier accumulation. Also, by employing different PM-inducing interlayers, it is possible to overcome limitations associated with the trap-assisted charge-carrier injection mechanism.