@article{ren_song_zhu_o'connor_dong_2023, title={All Electrohydrodynamic Printed Flexible Organic Thin Film Transistors}, volume={6}, ISSN={["2365-709X"]}, url={https://doi.org/10.1002/admt.202300410}, DOI={10.1002/admt.202300410}, abstractNote={AbstractThe demand of cost‐effective fabrication of printed flexible transistors has dramatically increased in recent years due to the need for flexible interface devices for various application including e‐skins, wearables, and medical patches. In this study, electrohydrodynamic (EHD) printing processes are developed to fabricate all the components of polymer‐based organic thin film transistors (OTFTs), including source/drain and gate electrodes, semiconductor channel, and gate dielectrics, which streamline the fabrication procedure for flexible OTFTs. The flexible transistors with top‐gate‐bottom‐contact configuration are fabricated by integrating organic semiconductor (i.e., poly(3‐hexylthiophene‐2,5‐diyl) blended with small molecule 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene), conductive polymer (i.e., poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate), and ion‐gel dielectric. These functional inks are carefully designed with orthogonal solvents to enable their compatible printing into multilayered flexible OTFTs. The EHD printing process of each functional component is experimentally characterized and optimized. The fully EHD‐printed OTFTs show good electrical performance with mobility of 2.86 × 10−1 cm2 V−1 s−1 and on/off ratio of 104, and great mechanical flexibility with small mobility change at bending radius of 6 mm and stable transistor response under hundreds of bending cycles. The demonstrated all printing‐based fabrication process provides a cost‐effective route toward flexible electronics with OTFTs.}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Ren, Ping and Song, Runqiao and Zhu, Yong and O'Connor, Brendan and Dong, Jingyan}, year={2023}, month={Jun} }
 @article{ren_dong_2023, title={Direct printing of conductive polymer PEDOT:PSS for foldable transient electronics}, volume={35}, ISSN={["2213-8463"]}, url={http://dx.doi.org/10.1016/j.mfglet.2023.08.024}, DOI={10.1016/j.mfglet.2023.08.024}, abstractNote={With the increased demand on portability, electronics have progressed from rudimentary flexible electronics to foldable electronics. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conductive polymer, is a promising material for achieving foldable electronics, due to its mechanical stability. In foldable electronics, however, inadequate physical adhesion between electrodes and substrates under folding deformation has been a challenge. It can cause interfacial delamination and electronic failure during the folding and unfolding processes. In this study, electrohydrodynamic (EHD) printing is utilized for the fast, low-cost, and high-resolution fabrication of PEDOT:PSS circuits onto polyvinyl alcohol (PVA) films to improve the interface binding force for foldable electronics. The morphology and electrical properties of PEDOT:PSS patterns with different printed conditions were experimentally investigated. The adhesion between the printed PEDOT:PSS circuits and the PVA film was characterized by tape adhesion test, and the electrical property remained almost unchanged after 50 peeling tests. We demonstrated excellent foldability of the printed electronics. After 4 folds (16 layers), the resistance of PEDOT:PSS circuits varied minimally, and the external LED lights remained operational while folding and unfolding. Moreover, using the water soluble and degradable PVA substrate, the printed circuits can be simply dissolved in water, which provide a promising approach toward transient electronics and green electronics, and reduce the electronic waste.}, journal={MANUFACTURING LETTERS}, publisher={Elsevier BV}, author={Ren, Ping and Dong, Jingyan}, year={2023}, month={Aug}, pages={215–220} }
 @article{ren_dong_2023, title={Electrohydrodynamic Printed Pedot:Pss/Graphene/Pva Circuits for Sustainable and Foldable Electronics}, volume={8}, ISSN={["2365-709X"]}, url={https://doi.org/10.1002/admt.202301045}, DOI={10.1002/admt.202301045}, abstractNote={AbstractThe generation of electronic waste (e‐waste) poses a significant environmental challenge, necessitating strategies to extend electronics’ lifespan and incorporate eco‐friendly materials to enable their rapid degradation after disposal. Foldable electronics utilizing eco‐friendly materials offer enhanced durability during operation and degradability at the end of their life cycle. However, ensuring robust physical adhesion between electrodes/circuits and substrates during the folding process remains a challenge, leading to interface delamination and electronic failure. In this study, electrohydrodynamic (EHD) printing is employed as a cost‐effective method to fabricate the eco‐friendly foldable electronics by printing PEDOT:PSS/graphene composite circuits onto polyvinyl alcohol (PVA) films. The morphology and electrical properties of the printed patterns using inks with varying graphene and PEDOT:PSS weight ratios under different printing conditions are investigated. The foldability of the printed electronics is demonstrated, showing minimal resistance variation and stable electronic response even after four folds (16 layers) and hundreds of folding and unfolding cycles. Additionally, the application of printed PEDOT:PSS/graphene circuit is presented as a resistive temperature sensor for monitoring body temperature and respiration behavior. Furthermore, the transient features and degradation of the PEDOT:PSS/graphene/PVA based foldable electronics are explored, highlighting the potential promise as transient electronics in reducing electronic waste.}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Ren, Ping and Dong, Jingyan}, year={2023}, month={Aug} }
 @article{song_ren_liu_zhu_dong_brendan t. o'connor_2023, title={Stretchable Organic Transistor Based Pressure Sensor Employing a Porous Elastomer Gate Dielectric}, volume={4}, ISSN={["2365-709X"]}, url={http://dx.doi.org/10.1002/admt.202202140}, DOI={10.1002/admt.202202140}, abstractNote={AbstractCompliant pressure sensors are a key technology for wearable electronics and haptic interfaces. Making transistors pressure‐sensitive provides an opportunity to combine sensing and matrix readout characteristics. However, there is typically a trade‐off in pressure sensitivity, complexity of fabrication, and mechanical resilience. To overcome these challenges, an all solution‐processed kirigami‐inspired stretchable organic thin film transistor (OTFT) based pressure sensor array is introduced. The OTFTs integrate several novel processing and design strategies that include electrohydrodynamic (EHD) jet‐printed Ag nanowire (NW) electrodes that are partially embedded in a polyimide (PI) matrix. The EHD printing provides fine pattern control and the NW/PI composite improves mechanical stability. The OTFTs are made pressure sensitive by employing a porous styrene‐ethylene‐butylene‐styrene gate dielectric achieved using a breath figure method. The pore density can be controlled to achieve tunable pressure sensitivity. The OTFTs are shown to maintain performance under a small bending radius (1 mm) and can sense applied pressure from 0.75 to 25 kPa. Finally, a cut pattern is introduced into the substrate that imparts stretchability while maintaining pressure sensor functionality. The integration of the design features and processing methods introduced in this work enables mechanically resilient stretchable pressure sensors.}, journal={ADVANCED MATERIALS TECHNOLOGIES}, publisher={Wiley}, author={Song, Runqiao and Ren, Ping and Liu, Yuxuan and Zhu, Yong and Dong, Jingyan and Brendan T. O'Connor}, year={2023}, month={Apr} }
 @article{ren_dong_2021, title={Direct Fabrication of VIA Interconnects by Electrohydrodynamic Printing for Multi-Layer 3D Flexible and Stretchable Electronics}, volume={6}, ISSN={["2365-709X"]}, url={https://doi.org/10.1002/admt.202100280}, DOI={10.1002/admt.202100280}, abstractNote={AbstractMulti‐layer electrical interconnects are critical for the development of integrated soft wearable electronic systems, in which functional devices from different layers need to be connected together by vertical interconnects. In this work, electrohydrodynamic (EHD) printing technology is studied to achieve multi‐layer flexible and stretchable electronics by direct printing vertical interconnects as vertical interconnect accesses (VIAs) using a low‐melting‐point metal alloy. The EHD printed metallic vertical interconnection represents a promising way for the direct fabrication of multilayer integrated electronics with metallic conductivity and excellent flexibility and stretchability. By controlling the printing conditions, vertical interconnects that can bridge different heights can be fabricated. To achieve reliable VIA connections under bending and stretching conditions, an epoxy protective structure is printed around the VIA interconnects to form a core‐shell structure. A stable electrical response is achieved under hundreds of bending cycles and during stretching/releasing cycles in a large range of tensile strain (0–40%) for the printed conductors with VIA interconnects. A few multi‐layer devices, including a multiple layer heater, and a pressure‐based touch panel are fabricated to demonstrate the capability of the EHD printing for the direct fabrication of vertical metallic VIA interconnects for flexible and stretchable devices.}, number={9}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Ren, Ping and Dong, Jingyan}, year={2021}, month={Jun} }
 @article{ren_liu_song_o'connor_dong_zhu_2021, title={Achieving High-Resolution Electrohydrodynamic Printing of Nanowires on Elastomeric Substrates through Surface Modification}, volume={3}, ISSN={["2637-6113"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85099220488&partnerID=MN8TOARS}, DOI={10.1021/acsaelm.0c00747}, abstractNote={Stretchable electronics based on nanomaterials has received much interest recently. However, it is challenging to print 1D nanomaterials (e.g., nanowires) with high resolution on stretchable elasto...}, number={1}, journal={ACS APPLIED ELECTRONIC MATERIALS}, publisher={American Chemical Society (ACS)}, author={Ren, Ping and Liu, Yuxuan and Song, Runqiao and O'Connor, Brendan and Dong, Jingyan and Zhu, Yong}, year={2021}, month={Jan}, pages={192–202} }