Design and Synthesis of Air-Stable p-Channel-Conjugated Polymers for High Signal-to-Drift Nitrogen Dioxide and Ammonia Sensing

Abstract

The development of high-performance-conjugated polymer-based gas sensors involves detailed structural tailoring such that high sensitivities are achieved without compromising the stability of the fabricated devices. In this work, we systematically developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by modifying the polymer backbone to achieve and rationalize enhancements in gas sensitivities and electronic stability in air. NO2- and NH3-responsive polymer-based organic field-effect transistors (OFETs) are described with improved air stability compared to all-thiophene conjugated polymers. Five DPP–fluorene-based polymers were synthesized and compared to two control polymers and used as active layers to detect a concentration of NO2 at least as low as 0.5 ppm. The hypothesis that the less electron-donating fluorene main-chain subunit would lead to increased signal/drift compared to thiophene and carbazole subunits was tested. The sensitivities exhibited a bias voltage-dependent behavior. The proportional on-current change of OFETs using a dithienyl DPP–fluorene polymer reached ∼614% for an exposure to 20 ppm of NO2 for 5 min, testing at a bias voltage of −33 V, among the higher reported NO2 sensitivities for conjugated polymers. Electronic and morphological studies reveal that introduction of the fluorene unit in the DPP backbone decreases the ease of backbone oxidation and induces traps in the thin films. The combination of thin-film morphology and oxidation potentials governs the gas-absorbing properties of these materials. The ratio of responses on exposure to NO2 and NH3 compared to drifts while taking the device through repeated gate voltage sweeps is the highest for two polymers incorporating electron-donating linkers connecting the DPP and thiophene units in the backbone, in this category of organic semiconductors. The responses to NO2 were much larger than that to NH3, indicating increased susceptibility to oxidizing vs reducing gases, and that the capability of oxidizing gases to induce additional charge density has a more dramatic electronic effect than when reducing gases create traps. This work demonstrates the capability of achieving improved stability with the retention of high sensitivity in conjugated polymer-based OFET sensors by modulating redox and morphological properties of polymer semiconductors by structural control.

Recent progress in lactam‐based polymer semiconductors for organic electronic devices

“…Katz et al reported air-stable and highly sensitive OFET sensors fabricated using DPP-fluorene-based polymers applicable for sensing NO 2 . 57 The gas absorption characteristics of OFET-based gas sensors are strongly influenced by the thin-film morphology and oxidation potential. The introduction of fluorene units into the DPP backbone reduces backbone oxidation and introduces traps in the thin film.…”

A highly selective electron affinity facilitated H2S sensor: the marriage of tris(keto-hydrazone) and an organic field-effect transistor

“…[16][17][18][19][20][21][22] Furthermore, combining the versatile DPP molecules with rigid structures such as naphthalene, thiophene and their analogous moieties results in donor-acceptor (D-A) architectures with homogenous crystal stacking and strong pi-pi intermolecular interactions. 18,20,22 Recently, many research groups have successfully integrated the DPP-based D-A polymers on organic field-effect transistor (OFET) platforms to sense NH 3 , [23][24][25][26] NO 2 , [27][28][29] H 2 S 30,31 and various VOC molecules. 20 Though DPP-based polymers are suitable candidates to sense harmful gases at the ppb level, the major setbacks of such sensors are their poor air stability and the aging effect, both of which lead to poor sensing performance.…”

The study of aggregation dynamics of conjugated polymer solutions in UV-vis absorbance spectra by considering the changing rate of average photon energy

“…Organic optoelectronic materials are widely used these days because they have unique merits such as low cost and flexibility that traditional inorganic materials do not have [1,2,3,4]. Conjugated polymer is one of the most common organic optoelectronic materials [5,6,7,8,9,10,11]. Normally, conjugated polymer-based devices are produced in conjugated polymer solutions and the aggregation process can influence properties of these devices [12,13,14,15].…”