Printed Energy Storage for Energy Autonomous Flexible Electronics

High-performance and efficient energy storage devices are a necessity for fulfilling the global demand of the growing market of distributed electronics, IoT, mobile electronic devices, electric vehicles, and many more. Supercapacitors and batteries are a priority for energy storage applications. In comparison with batteries, supercapacitors have longer cycle life and higher power density. In some cases, supercapacitors are integrated with batteries to increase electrical performance and efficiency. The aim of the research in this thesis is to develop and scale the design of a sustainable, low-cost, non-toxic, flexible, reliable, and eco-friendly energy storage device for energy-autonomous and distributed electronics platforms. The use of novel materials and a fabricating process for supercapacitor design were essential to achieve the goal of the research. With the use of low specific area electrode ink, the measured capacitance was 3–4 mF in dual cell supercapacitors. Similarly, a PET/Al laminated metal current collector has advantages due to high conductivity, low ESR, and the use of PC electrolyte (2.5 V/cell) to the target voltage range for low power BLE transmission applications. We also developed a PEDOT: PSS based polymer electrolytic capacitor as an alternative to supercapacitors, which demonstrated a way to print flexible capacitors of a few µF. This capacitor was modeled for low frequency applications such as smoothing and filtering. The second focus of the thesis was to perform a reliability study on the energy storage devices. This helps to observe the performance of the device in different situations, from normal to harsh environments. The supercapacitor’s electrical performance was stable over a wide temperature range from -40 °C to 100 °C. The supercapacitors maintain 100% retention for 10,000 bending cycles and a minimum bending radius of 0.41 cm, showing a high degree of flexibility. The device’s performance declined after thermal shock testing due to defects and cracks in the porous electrode because of rapid prolonged temperature cycling between -40 °C and 100 °C. The final part of the thesis is to harvest green energy from ambient surroundings using an organic photovoltaic (OPV) module or a piezoelectric transducer. The maximum indoor energy harvested with an OPV module and stored to the supercapacitor was 39 mJ. On the other hand, with a piezoelectric transducer, the maximum harvested energy was 1.1 mJ and peak power was 11.1 mW. The harvested energy was stored in our printed and flexible storage devices. We also demonstrated that the energy harvested was enough to power an LED driver circuit. Thus, these printed, low-cost, novel, and flexible devices open a door for the field of energy autonomous flexible electronics

Reliability test of fully printed and flexible organic electrolyte-based supercapacitor

As the demand for supercapacitors in various flexible and wearable energy sectors grows, reliability becomes a key aspect to consider. We report the fabrication and reliability study of printed, flexible organic electrolyte-based supercapacitors. The supercapacitor can be operated over a wide temperature range from −40 ◦C to 100 ◦C with excellent repeatability and stability. Thermal shock tests led to a defect in the electrode layer’s microstructure, which reduces the supercapacitor performance. Cyclic bending experiments show that the device has excellent robustness, mechanical flexibility, long-term electrical stability, and 100% capacitance retention up to 10 000bending cycles with a bending radius of 0.41 cm. Thus, the device is suitable for wearable and flexible energy storage applications over a wide temperature range.Peer reviewe

Polymer-based printed electrolytic capacitor and its circuitry application in a low pass filtering, rectifying and energy storage unit

We report the fabrication of flexible, printed polymer electrolytic capacitors and their implementation in printed electronics applications such as filtering, rectification and energy harvesting and storage. Capacitors were fabricated by depositing conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate onto porous anodized aluminum foil and yielded specific capacitance of 1 µF cm−2. This is far higher than values reported for printed plate capacitors and opens up the possibility of new applications in printed electronics related to filtering and smoothing at low frequencies. In this work, we have used printed polymer electrolytic capacitors to implement a resistor capacitor first order 1.03 kHz passive low pass filter, a full wave bridge rectifier circuit and a piezo-transducer energy harvester. An integrated full wave bridge rectifier based on these devices shows an efficiency of 80.5% at 1 kHz. When integrated with a vibration-motion based flexible piezoelectric transducer, the devices are able to generate and store about 1 mJ energy, which is a sufficient amount of energy for some low power electronics applications.acceptedVersionPeer reviewe

Solution processed schottky diode based on metal oxide

Metal oxides are of increasing interest in electronics because of their unique characteristics. They are used as semiconducting interfacial layer between the metal contacts and as active materials in many electrical components like thin film transistor, diodes, and field effect transistors. They have number of advantages like relatively low processing temperature, high carrier mobility, good electrical properties, good transparency, and large area uniformity. The precursor materials required to make solution processed semiconductor are cheap, easily available in the market, and easy to handle and process. In this thesis, we attempted to fabricate a Schottky diode based on solution processed metal oxide. The fabricated Schottky diode will be used in a rectifier circuit as low series resistance and highspeed switching device. The input AC signal to rectifier unit will be converted to DC and transfer power to the load circuit. Initially, different metals like aluminum, chromium, copper, gold, silver etc. were studied, analyzed and fabricated on the glass substrate. UV plasma and oxygen plasma surface treatments were explored to enhance film formation properties. Both lateral and vertical structures were studied. Vapor deposition technique was performed for deposition of metal contacts. The electrical characterization was carried out to find out whether the metal behaves as a Schottky or Ohmic contact to the metal oxide. Lateral and vertical structures were characterized with potentiostat, semiconductor analyzer and temperature stage at different biasing voltages. The measurements shows that all metals behaved more or less as Ohmic contacts. Aluminum and chromium gives Ohmic behavior at all temperatures. Some metals like chromium, copper, silver, gold etc. become injecting when the temperature rises. No true Schottky contact could be identified although this would be predicted according to the energy levels of the semiconductor and the work functions of the metals. Diode were fabricated using a variety of different parameters such as substrate treatment procedures, precursor, sintering method, and multi layer spin coating. The thickness of semiconducting layer and metal deposition thickness also varied during experiment. Unfortunately, no good vertical diodes could be fabricated. Due to the high current, it is believed that the devices are diode short-circuited because of pinholes. This is confirmed by microscopic images showing non-uniform layer, holes, cracks, and other defects

Integration of fully printed and flexible organic electrolyte-based dual cell supercapacitor with energy supply platform for low power electronics

We report the fabrication of flexible, printed dual cell supercapacitors (DCSCs) and their implementations in energy storage units providing peak power to portable devices. The use of organic electrolytes enhances higher capacity in both potential windows (2.5 V/cell) and the temperature ranges than the aqueous electrolytes, while propylene carbonate retains the advantages of low cost and low toxicity. The device delivered capacitance value between 3 and 4 mF, equivalent series resistance < 2 Ω, and very low leakage current of about 0.1 µA. We demonstrated the integration of an organic photovoltaic module (OPV) with an energy supply platform (ESP) and DCSCs for indoor light energy harvesting and storage. The maximum harvested energy was about 39 mJ. The energy is sufficient to provide peak power to portable devices and sensors. This was confirmed by powering an LED with our energy harvesting system. Mechanical deformation testing of DCSCs shows excellent mechanical stability, so that the device is well suited for flexible energy storage units. In a long-term cyclic stability test, the decrease in capacitance value was only 1% of the initial value after 10,000 cycles, indicating good durability and performance.publishedVersionPeer reviewe

Motion energy harvesting and storage system including printed piezoelectric film and supercapacitor

We report the study of piezoelectric transducer based on the copolymer P(VDF:TrFE) for energy harvesting based on deformation of the film. The bending characteristics, sensitivity, charge generation and frequency response at typical machine component frequencies of printed piezoelectric transducer was studied. Interestingly piezoelectric transducer shows response towards a different level of frequency and the bending forces. As expected, increased frequency and deformation yield increased energy harvesting. A harvester system integrated on flexible foil and comprising a printed piezoelectric element, integrated rectifier and printed supercapacitor was demonstrated, which harvests sufficient energy for low power measurements or radio transmission.acceptedVersionPeer reviewe

Selective atomic layer deposition on flexible polymeric substrates employing a polyimide adhesive as a physical mask

The rise of low-temperature atomic layer deposition (ALD) has made it very attractive to produce high- κ dielectric for flexible electronic devices. Similarly, selective deposition of ALD films is of great relevance for circuitry. We demonstrated a simple method of using a physical mask to block the film's growth in selected polymeric and flexible substrate areas during a low-pressure ALD process. A low-cost silicone adhesive polyimide tape was used to manually mask selected areas of bare substrates and aluminum strips deposited by evaporation. 190 cycles of aluminum oxide (Al 2O 3) and hafnium oxide (HfO 2) were deposited at temperatures ranging from 100 to 250 °C. Using x-ray photoelectron spectroscopy (XPS) analysis and energy dispersive x-ray spectroscopy (EDS), we showed that the mask was effective in protecting the areas under the tape. The mask did not show any modification of shape for an exposure of 10 h at 250 °C, hence keeping the form of the masked area intact. An analysis of the unmasked area by ellipsometry (632.8 nm) and x ray shows a regular film with a thickness variation under 2 nm for a given temperature and constant refractive index. EDS, selected-area XPS, and imaging XPS show an evident change of elemental content at the interface of two areas. By XPS, we established that the structure of the films was not affected by the mask, the films were stoichiometric, and there was no effect of outgassing from the adhesive film.publishedVersionPeer reviewe