Solution-processable organic photodiodes with high detectivity and thermal stability designed for visible or near-infrared CMOS image sensors

Abstract

We report materials and device designs of solution-processable organic photodiodes (OPDs) for visible or near-infrared (NIR) light detection compatible with CMOS image sensors (CIS), a large market for photodiodes. OPDs for CIS need to be reliably processable on silicon wafers with conventional methods such as spin coating, to have extremely low dark current even at a couple of negative voltages to utilize high gain read-out circuits, and to be stable under 150–250°C heating to endure module packaging. Those requirements have not been taken into an account for organic photovoltaics (OPVs) development, which assumed large area printing at low processing temperature (<150°C). We selected a conventional structure (p-i-n) with a polymeric hole transport layer (HTL) which we originally made for organic light-emitting diodes (OLEDs). The HTL is free from acids and dopants, contributing to excellent device stability. For visible OPDs, we applied a donor/acceptor blend originally made for OPVs, and obtained an external quantum yield (EQE) of ~85% at 450–700 nm with a dark current of ~10−7 mA/cm2. For NIR OPDs targeting 940 nm, we newly developed NIR absorbing non-fullerene acceptors (NFAs) having a sharp absorption peak at the wavelength to realize high EQE (~80%) and low thermal carriers at dark (~10−5 mA/cm2). Both type of OPDs retained 70–100% of their original EQEs after thermal annealing at <150°C for two hours. In the presentation video, we will show NIR images obtained from the imaging arrays.