Simple Interface Modification of Electroactive Polymer Film Electrodes

Understanding the role of interface properties is crucial in the search for alternative design strategies to optimize the efficiency, performance, and lifetime of both solid-state and redox active organic semiconductor devices. Recent advances have focused on controlling and tailoring interfacial effects on the morphology and molecular structure of the active film in multilayer devices triggering new developments in the area of interface engineering. Here, we demonstrate that an inorganic electrode/organic semiconductor interface modification using PEDOT:PSS as an interfacial material influences the charge and ion transport, capacitive, morphological, and color switching properties of a solution processed purple-to-clear switching electrochromic PProDOT-(CH2OEtHx)2 polymer film. We find that the barrier to charge transport from electrode to active material is lowered when adding this PEDOT:PSS film, allowing us to present a fully roll-to-roll compatible, simple, and versatile battery-type electrochromic device (ECD) design without the need for oxidizing the charge storage film, in combination with improved processing reproducibility. In addition to producing ECDs with minimal color differences compared to devices prepared in the more traditional and complicated manner, this new ECD design strategy provides competitive performance showing a consistent optical contrast of 50–55% and switching times of 2–4 s

How Low Can You Go? Defect Quantification at the 10¹⁵ cm^–3 Level in Mixed-Cation Perovskites Using Differential Pulse Voltammetry

Reactive defects in hybrid organic–inorganic metal halide perovskites that limit material functionality and durability, factors which ultimately dictate (opto)electronic device performance, are difficult to probe. Herein, we expand an electrochemical methodology for near-valence defect quantification, using a solid-state electrolyte “top contact,” to increase energy resolution and sensitivity via a differential pulse protocol. A new low level of detection of ca. 2 × 1015 cm–3 is reported for reactive defects in a triple-cation system. We confirmed that these defects are associated with mobile iodide ions in grain boundaries and at interfaces by using iodide and bromide spiked electrolytes. The detection limit for this electrochemical method is estimated to be ca. 1014 cm–3, well below that of many electrical or spectroscopic approaches. We predict this methodology lends itself to operando defect characterization during and after processing, at scale, of extremely low defect density perovskites and related optoelectronic platforms, ultimately providing an in-line approach to real-time performance and stability optimization

Defect Quantification in Metal Halide Perovskites Anticipates Photoluminescence and Photovoltaic Performance

Semiconductor material optimization requires quantification of performance and stability-dependent near-valence maximum and near-conduction minimum defects with sufficient energy resolution and sensitivity. Herein, we utilize a spectroscopy-electrochemistry approach to resolve the energy-distinct donor and acceptor defect concentrations in wide-gap (Cs.05FA.79MA.16)Pb(I.87Br.13)3 perovskites, benchmarked against photoluminescence and photovoltaic device performance. Monitoring charge transfer events to electron acceptor and donor molecules within solid electrolyte top contacts enables defect quantification below 1015 cm–3 at an energy resolution of 10 meV under device-relevant bias, well below levels reported by other methods. Further method sensitivity is demonstrated for defects arising from <2% formamidinium concentration modifications, mimicking compositional imperfections resulting from nonoptimized processing. This method provides the first complete perovskite energetic diagrams with small changes in composition, is nondestructive, compatible with in-line processing characterization, and will enable the semiconductor community to link molecular origins of defects with limitations in device performance across a wide array of optoelectronic platforms

Disentangling Redox Properties and Capacitance in Solution-Processed Conjugated Polymers

The unique ability of combined ionic and electronic transport in conjugated, semiconducting polymers has resulted in the emergence of a variety of redox-based technologies ranging from energy storage and conversion, to bioelectronics, to on-demand color control. Although conjugated polymers have been extensively studied for decades, the recent revival of organic bioelectronics, in particular, has demonstrated that there needs to be a better understanding of the interplay between mixed ion and electron transport and the underlying film morphology. Many of the conjugated polymers that are effectively doped electrochemically and that exhibit a combination of high capacitance, fast and reversible redox switching, and exceptional stability lack long-range order making it more challenging to evaluate how the morphology evolves as a function of oxidation state. Here, we demonstrate how readily accessible electrochemical and spectroscopic techniques can offer a great deal of insight into ion and electron transport in redox-active conjugated polymers regardless of their degree of order. Furthermore, we show how numerous redox properties, including onset of oxidation, capacitance, and conductance profile, of five dioxythiophene-based copolymers can be manipulated by the size and polarity of the functional groups that are incorporated to provide solution processability

Conducting Polymer Switches Permit the Development of a Frequency-Reconfigurable Antenna

Conjugated polymers (CPs) undergo a wide range of reversible intrinsic property changes including electrical conductivity, electromagnetic absorption, volume, and charge mobility upon electrochemical oxidation/reduction, which has made them popular as ON/OFF organic-based switchable materials. Recent studies on the insulating-to-conductive transition within CPs have paved the way for a next generation of flexible switches that permit the creation of “dynamic” electric circuits. Here, we present an approach to a low-voltage, low-power electrochemically controllable, switchable, and printable CP-based conductive element that acts as a platform for the configuration of frequency-reconfigurable radiative antennas. We demonstrate that the DC conductivity of a soluble PEDOT derivative, PE2, film can be switched electrochemically by 4 orders of magnitude across large insulating gaps up to 15 mm within 20 s. Its integration in a DC switching element that is incorporated along the poles of a half-wave dipole antenna structure is able to generate an AC resonant frequency switch, and thus a radiation frequency shift, in the microwave (i.e., 1–2 GHz) range. This type of printable antenna fills an important need for the demand of bandwidth that is growing beyond the crowded frequency spectrum, by relying on the development of frequency-reconfigurable antenna systems capable of dynamically tuning their spectral properties when desired