Ion Size-Dependent Electrochromism in Air-Stable Napthalenediimide-Based Conjugated Polymers.

Conjugated polymers (CPs) that show stable and reversible cation insertion/deinsertion under ambient conditions hold great potential for optoelectronic and energy storage devices. However, n-doped CPs are prone to parasitic reactions upon exposure to moisture or oxygen. This study reports a new family of napthalenediimide (NDI) based conjugated polymers capable of undergoing electrochemical n-type doping in ambient air. By functionalizing the NDI-NDI repeating unit with alternating triethylene glycol and octadecyl side chains, the polymer backbone shows stable electrochemical doping at ambient conditions. We systematically investigate the extent of volumetric doping involving monovalent cations of varying size (Li+, Na+, tetraethylammonium (TEA+)) with electrochemical methods, including cyclic voltammetry, differential pulse voltammetry, spectroelectrochemistry, and electrochemical impedance spectroscopy. We observed that introducing hydrophilic side chains on the polymer backbone improves the local dielectric environment of the backbones and lowers the energetic barrier for ion insertion. Surprisingly, when using Na+ electrolyte, the polymer films exhibit higher volumetric doping efficiency, faster-switching kinetics, higher optical contrast, and selective multielectrochromism when compared to Li+ or TEA+ electrolytes. Using well-tempered metadynamics, we characterize the free energetics of side chain-ion interactions to find that Li+ binds more tightly to the glycolated NDI moieties than Na+, hindering Li+ ion transport, switching kinetics, and limiting the films' doping efficiency.

Zinc Titanate Nanoarrays with Superior Optoelectrochemical Properties for Chemical Sensing.

In this report, the gas sensing performance of zinc titanate (ZnTiO3) nanoarrays (NAs) synthesized by coating hydrothermally formed zinc oxide (ZnO) NAs with TiO2 using low-temperature chemical vapor deposition is presented. By controlling the annealing temperature, diffusion of ZnO into TiO2 forms a mixed oxide of ZnTiO3 NAs. The uniformity and the electrical properties of ZnTiO3 NAs made them ideal for light-activated acetone gas sensing applications for which such materials are not well studied. The acetone sensing performance of the ZnTiO3 NAs is tested by biasing the sensor with voltages from 0.1 to 9 V dc in an amperometric mode. An increase in the applied bias was found to increase the sensitivity of the device toward acetone under photoinduced and nonphotoinduced (dark) conditions. When illuminated with 365 nm UV light, the sensitivity was observed to increase by 3.4 times toward 12.5 ppm acetone at 350 °C with an applied bias of 9 V, as compared to dark conditions. The sensor was also observed to have significantly reduced the adsorption time, desorption time, and limit of detection (LoD) when excited by the light source. For example, LoD of the sensor in the dark and under UV light at 350 °C with a 9 V bias is found to be 80 and 10 ppb, respectively. The described approach also enabled acetone sensing at an operating temperature down to 45 °C with a repeatability of >99% and a LoD of 90 ppb when operated under light, thus indicating that the ZnTiO3 NAs are a promising material for low concentration acetone gas sensing applications.

1,4-Dihydropyrrolo[3,2-b]pyrroles as a Single Component Photoactive Layer: A New Paradigm for Broadband Detection.

Single component organic photodetectors capable of broadband light sensing represent a paradigm shift for designing flexible and inexpensive optoelectronic devices. The present study demonstrates the application of a new quadrupolar 1,4-dihydropyrrolo[3,2-b]pyrrole derivative with spectral sensitivity across 350-830 nm as a potential broadband organic photodetector (OPD) material. The amphoteric redox characteristics evinced from the electrochemical studies are exploited to conceptualize a single component OPD with ITO and Al as active electrodes. The photodiode showed impressive broadband photoresponse to monochromatic light sources of 365, 470, 525, 589, 623, and 830 nm. Current density-voltage (J-V) and transient photoresponse studies showed stable and reproducible performance under continuous on/off modulations. The devices operating in reverse bias at 6 V displayed broad spectral responsivity (R) and very good detectivity (D*) peaking a maximum 0.9 mA W-1 and 1.9 × 1010 Jones (at 623 nm and 500 µW cm-2) with a fast rise and decay times of 75 and 140 ms, respectively. Low dark current densities ranging from 1.8 × 10-10 Acm-2 at 1 V to 7.2 × 10-9 A cm-2 at 6 V renders an operating range to amplify the photocurrent signal, spectral responsivity, and detectivity. Interestingly, the fabricated OPDs display a self-operational mode which is rarely reported for single component organic systems.