Cathode Interface Engineering for Heterogeneous Integration of Photodetection and Imaging Systems

The monolithic integration of organic photodiodes (OPDs) and advanced thin-film transistor (TFT) backplanes is paving the way for applications in photodetection and imaging. This study proposes a cathode interface engineering strategy utilizing a composite electron-transport layer (ETL) composed of amorphous indium–gallium–zinc oxide (IGZO) and poly[[9,9-bis[3′-(N,N-dimethylamino)propyl]-2,7-fluorene]-alt-2,7-(9,9-dioctylfluorene)] (PFN) films to fabricate optoelectronic devices. By synergistically combining the high electron mobility of IGZO with the excellent interfacial defect passivation capability of PFN, the optimized IGZO/PFN ETL enables a favorable energy-level alignment for electron injection at the interface. As a result, the fabricated OPD exhibits a low dark current density of 7.96 × 10–8 A cm–2 under a bias of −6 V, representing an order-of-magnitude reduction compared to PFN-based devices. When integrated with a high-mobility oxide TFT backplane, the 16 × 16 array sensor demonstrates the ability to detect weak light, with a light-to-dark current ratio exceeding 10 under an illumination of 370 nW cm–2 and a low power consumption of 37 pW pixel–1. The proposed sensor is fully compatible with mainstream production processes, which makes it advantageous for mass production.