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Growth Temperature and Electrochemical Performance in Vapor-Deposited Poly(3,4-ethylenedioxythiophene) Thin Films for High-Rate Electrochemical Energy Storage
摘要： Poly(ethylene 3,4-dioxythiophene (PEDOT) ?lms synthesized by oxidative chemical vapor deposition (oCVD) display strong electrochemical activity in the region from 2 to 4.2 V vs Li/Li+. By contrast, the more commonly studied PEDOT:polystyrenesulfonate (PSS) ?lms have negligible electrochemical activity in this region. For the oCVD ?lms, its small dopant anions (Cl?) that can easily enter and exit the polymer structure allow exchange with the Li+ counterion in solution, while for PEDOT:PSS, the poly(styrenesulfonate) dopant is a large macromolecule having substantially lower mobility. Here, we seek to elucidate the relationship between the structural characteristics of oCVD PEDOT thin ?lms and their electrochemical properties, particularly in Li-ion electrolyte systems. Speci?cally, we seek to rationally design the thin-?lm properties of oCVD PEDOT for high-rate performance and cycle life by varying the ?lm growth temperature. We observe that the dominant e?ect of increasing growth temperature is an in situ reorganization to an edge-on ?lm texture. In this case, the π?π stack is perpendicular to the substrate surface. The alternative dominant texture is face-on dominance, where the π?π stack is parallel to the substrate surface. For the ?rst time, we show that edge-on dominant ?lms provide higher speci?c capacities for a given charge/discharge rate. Furthermore, Raman spectroscopy demonstrates that edge-on dominant ?lms are less susceptible to oxidative damage after long-term cycling. This also enables edge-on dominant ?lms to maintain lower charge-transfer resistances compared to identically cycled face-on ?lms. Edge-on oCVD PEDOT is paired with molybdenum disul?de to demonstrate thick, optimized oCVD PEDOT thin ?lms in asymmetric devices for high-rate electrochemical energy storage.
关键词： electrochemical doping,oCVD,electrochemical energy storage,PEDOT,high-rate performance,conductive polymer
更新于2025-09-23 15:21:01
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Performance Improvement of Gate-Tunable Organic Light-Emitting Diodes with Electron-Transport and Hole-Blocking Layers
摘要： The current density and luminance of gate-tunable organic light-emitting diodes (OLEDs) can be modulated by application of an external gate potential. However, existing gate-tunable OLEDs require further optimization to make them suitable for practical use. In this work, the rapid electron conduction of 4,4’-bis(N-carbazolyl)-1,1’biphenyl (CBP) molecules under low operating potential is demonstrated in polymer electrolyte-coated super yellow (SY) polymer light-emitting diodes (PLEDs). This behavior is attributed to the facile electrochemical n-doping of CBP by the polymer electrolyte infiltrated into the SY PLED through the porous aluminum cathode. The field-modulated conductivity of CBP upon applying an external gate potential to electrolyte-gated (EG) PLEDs is demonstrated. These phenomena lead to the improved performance of EG SY PLEDs with a CBP electron-transport layer and 1,3,5-tris[(3-pyridyl)-phen-3-yl]benzene) (TmpypB) hole-blocking layer between the porous aluminum cathode and SY emissive layer, including low turn-on voltage (1.5 V), low current density leakage (0.01 mA/cm2), low off luminance (<0.01 cd/m2), saturated on-current density (2 mA/cm2) and on-luminance (100 cd/m2), and largely suppressed hysteresis. These results pave the path for practical application of EG OLEDs in displays, especially near-to-eye displays.
关键词： facile electrochemical doping,saturated on-current density and on-luminance,low off-current density leakage and off-luminance,suppressed hysteresis,near-to-eye displays,gate-tunable organic light-emitting diodes,grayscale displaying,porous electrodes
更新于2025-09-23 15:21:01
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Decoding the Polymer p–n Junction: Controlled Dedoping and Reverse Bias Electroluminescence
摘要： The polymer light-emitting electrochemical cell (PLEC) is a unique solid-state device possessing attractive attributes for low-cost applications, but also a junction structure that is still poorly understood. In a PLEC, the applied voltage causes in situ electrochemical p- and n-doping of the semiconducting polymer and the formation of a dynamic light-emitting p–n junction. Once the junction is fixed by cooling or chemical manipulation, the “frozen-junction” PLEC exhibits a unipolar electroluminescence (EL) and photovoltaic response. Repeated thermal cycling, however, can cause the frozen-junction PLEC to experience drastically enhanced EL under forward bias and the emergence of reverse bias EL. In this study, a combination of transport measurements and direct imaging is used to elucidate the origin of the mysterious reverse bias EL. A model is developed that explains the reverse bias EL as caused by the tunnel injection of electrons and holes from bandgap states into a dedoped “intrinsic” region between the p- and n-doped regions. The model explains the location, relative intensity, and evolution of EL under both forward and reverse bias. The results hint at a junction that is much narrower than previously resolved.
关键词： electrochemical doping,light-emitting polymer,p–n junction,electroluminescence
更新于2025-09-11 14:15:04
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A dynamic bipolar electrode array for visualized screening of electrode materials in light-emitting electrochemical cells
摘要： Charge injection at a metal/semiconductor interface is of paramount importance for many chemical and physical processes. The dual injection of electrons and holes, for example, is necessary for electroluminescence in organic light-emitting devices. In an electrochemical cell, charge transfer across the electrode interface is responsible for redox reactions and faradic current flow. In this work, we use polymer light-emitting electrochemical cells (PLECs) to visually assess the ability of metals to inject electronic charges into a luminescent polymer. Silver, aluminum or gold micro-discs are deposited between the two driving electrodes of the PLEC in the form of a horizontal array. When the PLEC is polarized, the individual discs functioned as bipolar electrodes (BPEs) to induce redox p- and n-doping reactions at their extremities, which are visualized as strongly photoluminescence-quenched growth in the luminescence polymer. The three metals initially generate highly distinct doping patterns that are consistent with differences in their work function. Over time, the doped regions continue to grow in size. Quantitative analysis of the n/p area ratio reveals an amazing convergence to a single value for all 39 BPEs, regardless of their metal type and large variation in the size of individual doped areas. We introduce the concept of a dynamic BPE, which transforms from an initial metal disc of fixed size to one that is a composite of p- and n-doped polymer joined by the initial metallic BPE. The internal structure of the dynamic BPE, as measured by the n/p area ratio, reflects only the properties of the mixed conductor of the PLEC active layer itself when the area ratio converges.
关键词： electrochemical doping,bipolar electrodes,light-emitting electrochemical cells,work function,electrode screening
更新于2025-09-09 09:28:46