Photomultiplication-Type Organic Photodetectors with High EQE-Bandwidth Product by Introducing a Perovskite Quantum Dot Interlayer

A photomultiplication (PM)-type organic photodetector (OPD) that exploits the ionic motion in CsPbI₃ perovskite quantum dots (QDs) is demonstrated. The device uses a QD monolayer as a PM-inducing interlayer and a donor–acceptor bulk heterojunction (BHJ) layer as a photoactive layer. When the device is illuminated, negative ions in the CsPbI₃ QD migrate and accumulate near the interface between the QDs and the electrode; these processes induce hole injection from the electrode and yield the PM phenomenon with an external quantum efficiency (EQE) >2000% at a 3 V applied bias. It is confirmed that the ionic motion of the CsPbI₃ QDs can induce a shift in the work function of the QD/electrode interface and that the dynamics of ionic motion determines the response speed of the device. The PM OPD showed a large EQE-bandwidth product >10⁶ Hz with a −3 dB frequency of 125 kHz at 3 V, which is one of the highest response speeds reported for a PM OPD. The PM-inducing strategy that exploits ionic motion of the interlayer is a potential approach to achieving high-efficiency PM OPDs.