High Detectivity in Photomultiplication-Type Organic Photodetectors: a Study on EQE and Dark Current Balance via Processing Methods

Abstract

Achieving high detectivity in photomultiplication-type organic photodetectors (PM-type OPDs) at low bias voltages is crucial for applications in imaging, biomedical monitoring, and other fields. In addition to the conventional one-step deposition method, the two-step deposition (TSD) method has emerged as a promising technique for fabricating active layers in organic solar cells and photodetectors. In this study, the balance between EQE and dark current in the PM-type OPDs is optimized by refining the processing methods, resulting in a remarkable detectivity of 9.32 × 1013 Jones. The formation of pure donor and acceptor phases near the electrodes in the TSD devices significantly reduces the dark current. Thermal admittance spectroscopy and impedance spectroscopy reveal an increase in the activation energy of trap states and a reduction in the density, contributing to improved performance. Additionally, an ultrafast response speed is achieved with a fall time of only 356.2 µs. Morphological analysis suggests a transition in molecular stacking from edge-on to face-on orientation, which is highly beneficial for enhancing the device's response speed. This work highlights the potential of TSD processing as a valuable approach for achieving high-performance PM-type OPDs.