From established to emergent technologies, doping plays a crucial role in all semiconducting devices. Doping could, theoretically, be an excellent technique for improving repressively low ...transconductances in n-type organic electrochemical transistors - critical for advancing logic circuits for bioelectronic and neuromorphic technologies. However, the technical challenge is extreme: n-doped polymers are unstable in electrochemical transistor operating environments, air and water (electrolyte). Here, the first demonstration of doping in electron transporting organic electrochemical transistors is reported. The ammonium salt tetra-n-butylammonium fluoride is simply admixed with the conjugated polymer poly(N,N'-bis(7-glycol)-naphthalene-1,4,5,8-bis(dicarboximide)-co-2,2'-bithiophene-co-N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide), and found to act as a simultaneous molecular dopant and morphology-additive. The combined effects enhance the n-type transconductance with improved channel capacitance and mobility. Furthermore, operational and shelf-life stability measurements showcase the first example of water-stable n-doping in a polymer. Overall, the results set a precedent for doping/additives to impact organic electrochemical transistors as powerfully as they have in other semiconducting devices.
A promising class of materials for applications that rely on electron transfer for signal generation are the n-type semiconducting polymers. Here we demonstrate the integration of an n-type ...conjugated polymer with a redox enzyme for the autonomous detection of glucose and power generation from bodily fluids. The reversible, mediator-free, miniaturized glucose sensor is an enzyme-coupled organic electrochemical transistor with a detection range of six orders of magnitude. This n-type polymer is also used as an anode and paired with a polymeric cathode in an enzymatic fuel cell to convert the chemical energy of glucose and oxygen into electrical power. The all-polymer biofuel cell shows a performance that scales with the glucose content in the solution and a stability that exceeds 30 days. Moreover, at physiologically relevant glucose concentrations and from fluids such as human saliva, it generates enough power to operate an organic electrochemical transistor, thus contributes to the technological advancement of self-powered micrometre-scale sensors and actuators that run on metabolites produced in the body.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Organic mixed conductors are increasingly employed in electrochemical devices operating in aqueous solutions that leverage simultaneous transport of ions and electrons. Indeed, their mode of ...operation relies on changing their doping (oxidation) state by the migration of ions to compensate for electronic charges. Nevertheless, the structural and morphological changes that organic mixed conductors experience when ions and water penetrate the material are not fully understood. Through a combination of electrochemical, gravimetric, and structural characterization, the effects of water and anions with a hydrophilic conjugated polymer are elucidated. Using a series of sodium‐ion aqueous salts of varying anion size, hydration shells, and acidity, the links between the nature of the anion and the transport and structural properties of the polymer are systematically studied. Upon doping, ions intercalate in the crystallites, permanently modifying the lattice spacings, and residual water swells the film. The polymer, however, maintains electrochemical reversibility. The performance of electrochemical transistors reveals that doping with larger, less hydrated, anions increases their transconductance but decreases switching speed. This study highlights the complexity of electrolyte‐mixed conductor interactions and advances materials design, emphasizing the coupled role of polymer and electrolyte (solvent and ion) in device performance.
Electrochemical, gravimetric, and X‐ray characterization of organic mixed conductors reveals that structure and transport properties depend on the nature of the electrolyte's ions. Morphological and microstructural changes in the polymer upon swelling and doping are investigated. Anions and water penetrate the bulk of the polymer and can intercalate in the crystallites. Smaller anions exhibit faster transistor switching but lower transconductance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Organic electrochemical transistors (OECTs) composed of organic mixed conductors can operate in aqueous, biological media and translate low-magnitude ionic fluctuations of biological origin into ...measurable electrical signals. The growing technological interest in these biotransducers makes the fundamental understanding of ion-to-electron coupling extremely important for the design of new materials and devices. One crucial aspect in this process that has been so far disregarded is the water taken up by the film during device operation and its effects on device performance. Here, using a series of the same electrolyte with varying ion concentrations, we quantify the amount of water that is incorporated into a hydrophilic p-type organic semiconductor film alongside the dopant anions and investigate structural and morphological changes occurring in the film upon electrochemical doping. We show that infiltration of the hydrated dopant ions into the film irreversibly changes the polymer structure and negatively impacts the efficiency, reversibility, and speed of charge generation. When less water is injected into the channel, OECTs exhibit higher transconductance and faster switching speeds. Although swelling is commonly suggested to be a necessity for efficient ion-to-electron transduction, this work uncovers the negative impact of a swollen channel material on the performance of accumulation mode OECTs and lays the foundation for future materials design.
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IJS, KILJ, NUK, PNG, UL, UM
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.
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IJS, KILJ, NUK, PNG, UL, UM
The charge accumulation properties of p-i-n perovskite solar cells were investigated
using three representative organic and inorganic hole transporting layer (HTL): (a)
...Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS, Al 4083), (b)
copper-doped nickel oxide (Cu:NiOx), and (c) Copper oxide (CuO). Through impedance
spectroscopy analysis and modelling, it is shown that charge accumulation is decreased in
the HTL/perovskite interface, between PEDOT:PSS to Cu:NiOx and CuO. This was indicative
from the decrease in double layer capacitance (Cdl) and interfacial charge accumulation
capacitance (Cel), resulting in an increase to recombination resistance (Rrec), thus
decreased charge recombination events between the three HTLs. Through AFM measurements, it
is also shown that the reduced recombination events (followed by the increase in Rrec) are
also a result of increased grain size between the three HTLs, thus reduction in the grain
boundary area. These charge accumulation properties of the three HTLs have resulted in an
increase to the power conversion efficiency between the PEDOT:PSS (8.44%), Cu:NiOx
(11.45%), and CuO (15.3%)-based devices.
Perovskite photovoltaics (PVs) have attracted attention because of their excellent power conversion efficiency (PCE). Critical issues related to large‐area PV performance, reliability, and lifetime ...need to be addressed. Here, it is shown that doped metal oxides can provide ideal electron selectivity, improved reliability, and stability for perovskite PVs. This study reports p‐i‐n perovskite PVs with device areas ranging from 0.09 cm2 to 0.5 cm2 incorporating a thick aluminum‐doped zinc oxide (AZO) electron selective contact with hysteresis‐free PCE of over 13% and high fill factor values in the range of 80%. AZO provides suitable energy levels for carrier selectivity, neutralizes the presence of pinholes, and provides intimate interfaces. Devices using AZO exhibit an average PCE increase of over 20% compared with the devices without AZO and maintain the high PCE for the larger area devices reported. Furthermore, the device stability of p‐i‐n perovskite solar cells under the ISOS‐D‐1 is enhanced when AZO is used, and maintains 100% of the initial PCE for over 1000 h of exposure when AZO/Au is used as the top electrode. The results indicate the importance of doped metal oxides as carrier selective contacts to achieve reliable and high‐performance long‐lived large‐area perovskite solar cells.
Doped metal oxides provide ideal electron selectivity, improved lifetime, and reliability for large‐area perovskite‐based photovoltaics. The proposed aluminum‐doped zinc oxide electron selective contact provides suitable energy levels for carrier selectivity and stability, neutralizes the presence of pinholes, provides intimate interfaces, and maintains high power conversion efficiency for large‐area solar cell devices.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Exposure to accelerated humidity lifetime conditions has been proved to have detrimental effects on organic photovoltaics (OPV) performance, because of the deterioration of the electrodes of the ...device rather than the active layer. Normal and inverted OPV devices are investigated in order to identify their main degradation mechanisms under accelerated humidity lifetime conditions. Reverse engineering can be a useful technique to probe main degradation mechanisms of the top electrode of both normal and inverted organic photovoltaic (OPVs). By using reverse engineering methods, we show that the major degradation mechanism of inverted OPVs under accelerated humidity lifetime conditions, is due to PEDOT:PSS hole selective top contact.
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•We study electrode degradation mechanisms of OPVs under humidity.•Reverse engineering is a useful tool to identify degradation mechanisms.•Degradation mechanisms for normal and inverted OPVs are discussed.•The major degradation of inverted OPVs under humidity conditions is due to PEDOT:PSS.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Solution processed inverted organic photovoltaics (OPVs) usually use (Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS derivatives as hole selective contact. In this study the effect ...of different PEDOT:PSS formulations, Al4083, PH and PH500 in inverted structured OPVs is investigated. Through detailed device physics analysis PEDOT:PSS PH is proposed as most suitable hole selective contact for inverted OPVs device function. Furthermore, PEDOT:PSS PH hole selective contact is treated with 3 different wetting agents, Zonyl FS-300 fluorosurfactant (Zonyl), 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate (Dynol) and Zonyl:Dynol mixture and the corresponding non-encapsulated inverted OPVs investigated under accelerated humidity lifetime conditions. The inverted OPVs incorporating PEDOT:PSS:Zonyl hole selective contact shown limitations on humidity lifetime performance due to the poorest adhesion properties of Zonyl-treated PEDOT:PSS PH compared with Dynol and Zonyl/Dynol mixture treaded PEDOT:PSS PH.
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•The effect of PEDOT:PSS formulations, Al4083, PH and PH500 in inverted OPVs is investigated.•Conductivity of 10−2S/cm and PEDOT: PSS content (1:2.5) are suitable values for hole selectivity.•PEDOT:PSS/Zonyl-based inverted OPVs show limited humidity lifetime due to poor adhesion.•PEDOT:PH treated with Zonyl:Dynol is the most suitable hole selective contact for high performance inverted OPVs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability ...investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly4,8-bis(2-ethylhexyl)oxybenzo1,2-b:4,5-b′dithiophene-2,6-diyl3-fluoro-2-(2-ethylhexyl)carbonylthieno3,4-bthiophenediyl (PTB7), and thieno3,2-bthiophene-diketopyrrolopyrrole (DPPTTT) blended with 6,6-phenyl C71-butyric acid methyl ester (PC70BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC70BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC70BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC70BM/MoO3 interface is the main origin of failure of the P3HT:PC70BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.
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IJS, KILJ, NUK, PNG, UL, UM
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