Ohayon David, Savva Achilleas, Du Weiyuan, Paulsen Bryan D, Uguz Ilke, Ashraf Raja S, Rivnay Jonathan, McCulloch Iain, Inal Sahika
Organic Bioelectronics Laboratory, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
KAUST Solar Center (KSC), Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
ACS Appl Mater Interfaces. 2021 Jan 27;13(3):4253-4266. doi: 10.1021/acsami.0c18599. Epub 2021 Jan 13.
n-Type (electron transporting) polymers can make suitable interfaces to transduce biological events that involve the generation of electrons. However, n-type polymers that are stable when electrochemically doped in aqueous media are relatively scarce, and the performance of the existing ones lags behind their p-type (hole conducting) counterparts. Here, we report a new family of donor-acceptor-type polymers based on a naphthalene-1,4,5,8-tetracarboxylic-diimide-bi-thiophene (NDI-T2) backbone where the NDI unit always bears an ethylene glycol (EG) side chain. We study how small variations in the side chains tethered to the acceptor as well as the donor unit affect the performance of the polymer films in the state-of-the-art bioelectronic device, the organic electrochemical transistor (OECT). First, we find that substitution of the T2 core with an electron-withdrawing group (i.e., methoxy) or an EG side chain leads to ambipolar charge transport properties and causes significant changes in film microstructure, which overall impairs the n-type OECT performance. We thus show that the best n-type OECT performer is the polymer that has no substitution on the T2 unit. Next, we evaluate the distance of the oxygen from the NDI unit as a design parameter by varying the length of the carbon spacer placed between the EG unit and the backbone. We find that the distance of the EG from the backbone affects the film order and crystallinity, and thus, the electron mobility. Consequently, our work reports the best-performing NDI-T2-based n-type OECT material to date, i.e., the polymer without the T2 substitution and bearing a six-carbon spacer between the EG and the NDI units. Our work provides new guidelines for the side-chain engineering of n-type polymers for OECTs and insights on the structure-performance relationships for mixed ionic-electronic conductors, crucial for devices where the film operates at the aqueous electrolyte interface.
n型（电子传输）聚合物可以形成合适的界面来转换涉及电子产生的生物事件。然而，在水性介质中进行电化学掺杂时稳定的n型聚合物相对较少，并且现有n型聚合物的性能落后于其p型（空穴传导）同类聚合物。在此，我们报道了一类基于萘-1,4,5,8-四羧酸二酰亚胺-联噻吩（NDI-T2）主链的新型供体-受体型聚合物，其中NDI单元总是带有一个乙二醇（EG）侧链。我们研究了连接到受体以及供体单元的侧链的微小变化如何影响聚合物薄膜在最先进的生物电子器件——有机电化学晶体管（OECT）中的性能。首先，我们发现用吸电子基团（即甲氧基）或EG侧链取代T2核会导致双极性电荷传输特性，并引起薄膜微观结构的显著变化，这总体上会损害n型OECT的性能。因此，我们表明性能最佳的n型OECT聚合物是在T2单元上没有取代的聚合物。接下来，我们通过改变置于EG单元和主链之间的碳间隔基的长度，将氧与NDI单元的距离作为一个设计参数进行评估。我们发现EG与主链的距离会影响薄膜的有序性和结晶度，进而影响电子迁移率。因此，我们的工作报道了迄今为止性能最佳的基于NDI-T2的n型OECT材料，即没有T2取代且在EG和NDI单元之间带有六个碳间隔基的聚合物。我们的工作为用于OECT的n型聚合物的侧链工程提供了新的指导方针，并为混合离子-电子导体的结构-性能关系提供了见解，这对于薄膜在水性电解质界面工作的器件至关重要。
