METAL ORGANIC FRAMEWORK BROADBAND PHOTODETECTORS

Abstract

This study investigates the synthesis and characterization of a high surface area zinc porphyrin metal-organic framework (ZnTCPP MOF) and its nanocomposite, focusing on their application in broadband photodetectors for self-powered and photomultiplication-based devices. Metal-organic frameworks (MOFs) are promising materials with tunable optical and electrical properties. Their large surface area, stability, and ease of synthesis techniques makes them suitable for integration in both inorganic and organic device fabrication. ZnTCPP, is widely used in photocatalysis applications. The porphyrin linker present in this MOF enables absorption in wide range of spectrum. Thus, making it an ideal candidate for broadband photodetection. ZnTCPP can enhance the performance of existing organic broadband photodetectors. Previous research has only explored the use of ZnTCPP in a heterojunction with P3HT and PCBM for solar cells. In this study, initially ZnTCPP nanosheets with a very high surface area were synthesized and used in combination with P3HT and PCBM as the active layer in a selfpowered photodetector. The device structure was ITO/PEDOT/Active Layer/Al. The inclusion of ZnTCPP improved the performance compared to the traditional bulk heterojunction. Inverted structures are known for better performance parameters. For devices with an inverted structure, a thin film of TiO2 was optimized using a sol-gel process. Although ZnTCPP MOF did not exhibit photomultiplication in standard structures, this phenomenon was observed in inverted structures. The Photomultiplication is attributed to interface trap states provided by TiO2. The devices showed photomultiplication under both bias conditions, but in forward bias, the current does not follow ideal on-off behaviour upon illumination due to substantial hole accumulation at the TiO2/P3HT interface. While these devices exhibited iii photomultiplication, the on-off ratio was low in reverse bias. Also, external quantum efficiency (EQE) significantly reduces after insertion of ZnTCPP. To address this, the study explored a nanocomposite of ZnTCPP and ZnO nanoparticles, with varying weight percentages of ZnO added during synthesis. The resulting broadband photodetector showed significant improvements in several parameters, including (EQE), on-off ratio, rise time, and fall time. This indicates that incorporating porphyrin MOFs into traditional organic devices can enhance the overall performance of broadband photodetectors.