Commercializing Materials for Solution-Processable Near-Infrared and Short-Wave Infrared Photodiodes: Challenges and Solutions in Performance, Process and Production

Solution-processed near-infrared (NIR) and short-wave infrared (SWIR) organic photodiodes (OPDs) hold great promise as they can offer higher external quantum efficiency (EQE) for infrared light detection compared to silicon-based photodiodes, at a lower cost than InGaAs-based alternatives. However, commercialization of these OPDs faces hurdles in materials development and device engineering. In this presentation, we discuss the challenges encountered during our decade-long research as a chemical company, dedicated to providing reliable organic semiconductor materials to the market. These challenges can be classified into three categories: lab-scale device performance, fabrication process, and industrial-scale production.<br/><br/>To meet demands for higher sensing performance, particularly higher EQE with suppressed dark current, we have developed novel materials for the photo-active layer (PAL) and the hole transport layer (HTL) positioned beneath it. The PAL consists of a blend of donor polymers and non-fullerene acceptors (NFAs) which absorb lights in the NIR and SWIR regions. An OPD designed for sensing NIR exhibited an EQE of 80% at 940 nm with 5 × 10⁻⁶ mA/cm⁻², while another OPD designed for sensing SWIR exhibited an EQE of 45% at 1100 nm with a dark current of 4 × 10⁻⁵ mA/cm⁻². We will present updates on the device performances. The achieved low dark current in these devices can be partly attributed to the material design of the HTL. The HTL comprises a polymer with thermal-crosslinking moiety, enabling a wider range of solvent choice for PAL deposition, eliminating the need for “orthogonal” solvents. The HTL contains no additives or catalysts for cross-linking, which ensures minimal contamination in both the HTL and PAL, preserving the desired hole mobility. This HTL design is also successfully applied to our organic light emitting diodes and organic/perovskite photovoltaics technologies.<br/><br/>Addressing the process-related requirements in the electronics industry, we optimized the ink formulations for the PAL and HTL without the use of halogenated solvents. These inks maintain consistent device performance for over three months. When fabricating OPDs on CMOS readout circuits on a silicon wafer, spin-coating emerges as the preferred choice due to its widespread utilization in the semiconductor industry's patterning process. We have achieved successful spin coating of our HTL on an 8-inch silicon wafer with a thickness variation of less than 3 nm across the entire layer. The PAL inks have been optimized to prevent dewetting on the HTL and ensure a smooth coating on top. To withstand subsequent reflow soldering and encapsulation processes, the OPD-CMOS stacks are heated to at least 200°C. We will present various technologies implemented to avoid thermal degradation and crystallization of NFAs during the heating process.<br/><br/>As for manufacturing, stringent quality control measures are imperative for reliable commercial production. The organic semiconductor community widely recognizes the batch-to-batch variations in semiconductor performance using commercially-available or laboratory-made organic semiconductors. We will discuss our approach to address this critical issue.