Improving The Performance of Organic Photodetectors with Removable Ultrathin Top Electrodes

Recently, Organic photodetectors (OPD) with removable top electrode have attracted much attention for systematic analysis of the degradation of the device. This new structure of OPD consist of a bottom and top electrode sheets. The bottom electrode sheet was fabricated by forming a transparent electrode, electron transport layer (ETL) and active layer on a glass or flexible substrate. The top electrode sheet contains an electrode and hole transport layer (HTL) on another substrate. The top electrode sheet can be attached to the bottom electrode sheet by intermolecular forces. The top electrode sheet can be easily removed from the bottom electrode sheet without damaging the organic semiconductor layer. Using this structure, our group has succeeded in directly and continuously evaluating the electrical properties of the OPD and the crystallinity and chemical analysis of the interface between active layer and HTL before and after operating the device by removing the top electrode sheet.^[1]In previous report, the thickness of the top electrode sheet is 1 mm. This thicker substrate shows the weak adhesion between the active layer and the HTL. So, the device cannot be operated as an OPD without applying pressure. However, continuous pressure distorts the active layer and accelerate the degradation and possibly change the crystallinity.^[2] Therefore, it is important to develop OPD with removable top electrode that can be operated without applying pressure.<br/>In this study, we developed OPD with removable top electrode that can be operated without pressure by using an ultrathin rubber sheet as a substrate of top electrode. The ultrathin rubber sheet is an extremely tough, self-adhesive and gas-permeable polydimethylsiloxane (PDMS) nanofilm with a thickness of approximately 700 nm, fabricated by dip coating a thin polyurethane nanofiber sheet with PDMS.^[3] The fabricated OPD shows 67% EQE at 550 nm and -5 V (light intensity is 6.7×10^-3 mW/cm²) without applying pressure. The specific detectability of OPD is as high as 2.9×10¹² Jones. The photocurrent and dark current at -2 V were changed 42.9 % and 117%, respectively after 100 cycles of lamination and delamination the top electrode sheet.<br/><br/>Reference<br/>[1] Shimanoe, et al. “Development of Air Stable Photomultiplication Type Organic Photodetector and Analysis of Active Layer using Removable Top Electrode,” <i>Advanced Electronic Materials</i>, 2200651, 2022.<br/>[2] Cheng, Pei, et al. "Stability of organic solar cells: challenges and strategies." <i>Chemical Society Reviews</i> 45.9 , 2544-2582, 2016.<br/>[3] Wang, Yan, et al. "Robust, self-adhesive, reinforced polymeric nanofilms enabling gas-permeable dry electrodes for long-term application." <i>Proceedings of the National Academy of Sciences</i> 118.38, e2111904118, 2021.