In this study, we focus on the precise control of electronic and ink properties for hole transport materials (HTM) and photoactive materials, consisting of p-type polymers (donors) and non-fullerene acceptors (NFA), to develop solution processable near-infrared (NIR) and short-wave infrared (SWIR) organic photodiodes(OPDs) with consistent performance over different batches. We observed fluctuations in the turn-on voltage of NIR-OPD devices when using different batches of our HTM. Regression analysis revealed a strong correlation between the turn-on voltage and specific factors in the polymer. By implementing an improved purification scheme, we successfully suppressed these fluctuations. Moreover, we investigated the impact of p-type polymer structure and properties on device performance and solubility in non-halogenated solvents. A trade-off between molecular weight and EQE of NIR-OPDs was identified in a commercially purchased polymer. However, by optimizing the synthesis pathway, we achieved compatibility between these parameters in our polymer and extended the ink storage period to over three months without compromising EQE and dark current. Additionally, we introduce a novel NFA, IR6, which exhibits an impressive EQE of 45% at 1100 nm with a dark current of 4 × 10 −5 mA/cm−2 . These advancements in precise material control and novel NFA offer promising prospects for the commercialization of solution-processable NIR-OPDs, making them viable candidates for high-performance near-infrared sensing applications.
We report ink formulations for solution-processable near-infrared organic photodiodes (OPDs) to fabricate organic CMOS image sensors on silicon wafers. The ink for the hole transport layer, which consists of cross-linkable semiconducting polymers, fully covers an 8-inch silicon wafer with less than 3 nm of variation in thickness by spin-coating. The ink is stable over several months. For the ink for the active layer, new additives are found to reduce micrometer size phase separation of donor and acceptor semiconductors after thermal annealing, which is fatal to achieve pixel to pixel reproducibility. Both inks are free from halogenated solvents.
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.
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