Flexible Blade-Coated Devices—Dual Functionality via Simultaneous Deposition

Advancements in printing techniques have enabled a new generation of low-cost and large-area flexible electronics. Printing methods have been used to fabricate a wide range of organic electronics including light-emitting diodes (OLEDs), photodiodes (OPDs), solar cells (OSCs), and thin-film transistors (OTFTs). Printed optoelectronic systems that integrate a combination of light sources and detectors require each component to be fabricated in separate processing steps. Furthermore, stacking of several flexible components that is used in integration reduces the overall flexibility of the system. In this work, we utilize surface-energy-patterning (SEP) to enable simultaneous blade coating of OPD and OLED films side-by-side on a single substrate. Hydrophilic printing regions and hydrophobic barriers are patterned on the substrate through a series of surface treatment steps, enabling the isolation of inks on the surface of the substrate. Consequently, the solution concentration of each deposited ink can be used to independently tune properties of the isolated films. Here, various active layer ink concentrations were investigated to optimize OPD bulk heterojunction (BHJ) and OLED emissive layer (EML) film thicknesses and thus optimize the performance of each device. BHJ solution concentrations of 40, 30 and 20 mg/ml were used for OPDs and emissive layer EML solution concentrations of 12, 10 and 8 mg/ml were used for OLEDs. The maximum OPD spectral responsivity of 0.33 A/W at 800 nm was printed from a BHJ solution concentration of 40 mg/ml. The optimized OPD exhibits a dark current of 22 nA/cm² at a bias of -1 V, EQE of 30 to 50% across 400 to 850 nm, linear dynamic range of 88 dB, and high cut-off frequency of 300 kHz. A maximum OLED luminance of 7000 cd/m² at an applied bias of 8 V was printed from an EML solution concentration of 10 mg/ml. The optimized OLED exhibits a turn-on voltage of 3.1 V, radiance of 35.7 W/m²/sr at 8V from an emission area of 7.4 mm², and EQE and luminous efficacy of 1% and 1 lm/W, respectively. Overall, our technique enables the deposition of two functionally distinct devices in a single deposition step without comprising the performance of each device. In this process, adjusting ink concentration also allows the use of a developed printing process to be adapted to a new ink, decreasing optimization necessary to fabricate new systems. This method demonstrates an important step towards large-area fabrication of printed electronics where devices with different functionalities are better integrated.