Trap-dominated nitrogen dioxide and ammonia responses of air-stable p-channel conjugated polymers from detailed bias stress analysis
Trap-dominated nitrogen dioxide and ammonia responses of air-stable p-channel conjugated polymers from detailed bias stress analysis
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DOI：
10.1039/d0tc05458e
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发表时间：
2021-02
影响因子：
6.4
通讯作者：
T. Mukhopadhyaya;H. Katz
中科院分区：
文献类型：
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作者：
T. Mukhopadhyaya;H. Katz
共轭聚合物气体传感器的改进涉及对主链电子结构和固态微观结构的微调，以结合高稳定性和灵敏度。我们之前通过引入各种芴连接体开发了一系列基于二酮吡咯并吡咯（DPP）的聚合物半导体，以研究控制空气中以及栅极和漏极偏压应力下的气体敏感性和电子稳定性的趋势和机制。使用二噻吩基 DPP-芴聚合物的有机场效应晶体管 (OFET) 连续暴露于 0.5-20 ppm NO2 5 分钟后，其导通电流比例变化达到约 600%，并且在动态偏置应力下也具有高响应漂移比。在目前的工作中，我们首次明确了静态偏置应力和陷阱在传感过程中的作用。除了电子结构之外，分子和微观结构水平的缺陷控制着形成和维持陷阱的能力以及随后的主链掺杂性。据观察，具有扭曲主链的聚合物能够产生能量上较宽的陷阱分布，而具有高度固态有序度的聚合物则表现出形成能量上较窄的陷阱分布的倾向，并且在暴露于空气时陷阱会快速钝化。聚合物在偏置应力作用下陷阱的稳定性和能量分布与电子结构和固态堆积有关；并进一步评估了 NO2 和 NH3 填充/创建陷阱的能力。在 VG = VD = -80 V 的偏置应力条件下，聚合物在 NO2 辅助恢复和空气辅助恢复后均保持其 NO2 敏感性。为了验证 NH3 产生陷阱的能力，通过在正栅极电压的帮助下充电，从 OFET 传感器上擦除陷阱，从而与空气对照相比，导致 NH3 响应增加。这项工作表明，电荷陷阱填充和生成响应机制是主要的，甚至可以用于对蒸汽的更高响应。主干掺杂性似乎对此类具有工程缺陷的聚合物半导体的响应影响较小。最后，偏置应力通常不会妨碍此类 OFET 蒸汽传感器恢复其原始灵敏度。
The improvement of conjugated polymer-based gas sensors involves fine tuning the backbone electronic structure and solid-state microstructure to combine high stability and sensitivity. We had previously developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by introducing a variety of fluorene linkers to study the trends and mechanisms governing gas sensitivities and electronic stability in air and under gate and drain bias stress. The proportional on-current change of organic field-effect transistors (OFETs) using a dithienyl DPP–fluorene polymer reached ∼600% for a sequential exposure from 0.5–20 ppm of NO2 for 5 minutes and also a high response-to-drift ratio under dynamic bias stress. In the present work we specify the roles of static bias stress and traps in the sensing process for the first time. Apart from electronic structure, defects at the molecular and microstructural levels govern the ability to form and sustain traps and subsequent backbone dopability. A polymer with a twisted backbone was observed to be capable of creating an energetically broad trap distribution while a polymer with a high degree of solid-state order shows a tendency to form an energetically narrow trap distribution and a fast passivation of traps on exposure to air. The stability and energetic distribution of traps on subjecting the polymers to bias stress was related to electronic structure and solid-state packing; and the ability of NO2 and NH3 to fill/create traps further was evaluated. At a bias stress condition of VG = VD = −80 V, the polymers retain their NO2 sensitivity both post NO2-aided recovery and air-aided recovery. In order to verify the ability of NH3 to create traps, traps were erased from the OFET sensors by charging with the aid of a positive gate voltage leading to an increase in the NH3 response when compared to air controls. This work demonstrates that the charge-trap filling and generation response mechanism is predominant and can even be leveraged for higher responses to vapors. Backbone dopability appears to be a minor contributor to responses in this category of polymeric semiconductors with engineered defects. Finally, bias stress generally does not preclude this category of OFET vapor sensors from recovering their original sensitivities.