Thermal and Mechanical Energy Harvesting Using Lead Sulfide Colloidal Quantum Dots

The human body is an abundant source of energy in the form of heat and mechanical movement. The ability to harvest this energy can be useful for supplying low-consumption wearable and implantable devices. Thermoelectric materials are usually used to harvest human body heat for wearable devices; however, thermoelectric generators require temperature gradient across the device to perform appropriately. Since they need to attach to the heat source to absorb the heat, temperature equalization decreases their efficiencies. Moreover, the electrostatic energy harvester, working based on the variable capacitor structure, is the most compatible candidate for harvesting low-frequency-movement of the human body. Although it can provide a high output voltage and high-power density at a small scale, they require an initial start-up voltage source to charge the capacitor for initiating the conversion process. The current methods for initially charging the variable capacitor suffer from the complexity of the design and fabrication process. In this research, a solution-processed photovoltaic structure was proposed to address the temperature equalization problem of the thermoelectric generators by harvesting infrared radiations emitted from the human body. However, normal photovoltaic devices have the bandgap limitation to absorb low energy photons radiated from the human body. In this structure, mid-gap states were intentionally introduced to the absorbing layer to activate the multi-step photon absorption process enabling electron promotion from the valence band to the conduction band. The fabricated device showed promising performance in harvesting low energy thermal radiations emitted from the human body. Finally, in order to increase the generated power, a hybrid structure was proposed to harvest both mechanical and heat energy sources available in the human body. The device is designed to harvest both the thermal radiation of the human body based on the proposed solution-processed photovoltaic structure and the mechanical movement of the human body based on an electrostatic generator. The photovoltaic structure was used to charge the capacitor at the initial step of each conversion cycle. The simple fabrication process of the photovoltaic device can potentially address the problem associated with the charging method of the electrostatic generators. The simulation results showed that the combination of two methods can significantly increase the harvested energy

Survey of energy scavenging for wearable and implantable devices

This paper reviews state-of-the-art methods of energy harvesting for implantable and wearable devices based on the available mechanical and heat energy sources in the human body. The development of a compatible and sustainable power supply for wearable and implantable devices is a demand to realize their continuous and high-performance operation, minimize the need for external energy sources, and increase the lifetime of the devices. Heat and mechanical movement are two available and reliable energy sources in the human body. Since mechanical and heat energy harvesting methods have been extensively studied over the past decades, researchers focus on developing techniques to integrate these energy harvesters with implantable and wearable electronics. Therefore, energy requirement for wearable and implantable devices, available energy level from the human body, and convenience and feasibility of the implementation are taken into account to provide full or partial power support. This survey aims to present recent findings and developments in the field of energy harvesting from continuous heat source and mechanical movements of the human body. In particular, working principles, technical details, and current status as well as issues and challenges of energy harvesting from human body including thermoelectric, photovoltaic, piezoelectric, electrostatic, electromagnetic, and triboelectric harvesters are discussed

A hybrid structure for energy harvesting from human body thermal radiation and mechanical movement

In this work, a hybrid structure was proposed to harvest both mechanical and heat energy sources available in the human body. The device is designed to harvest both the thermal radiation of the human body based on the proposed solution-processed photovoltaic structure and the mechanical movement of the human body based on an electrostatic generator. The photovoltaic structure is used to charge the capacitor at the initial step of each conversion cycle. The simple fabrication process of the photovoltaic device can potentially address the problem associated with the charging method of the electrostatic generators. The simulation results showed that the combination of two methods can significantly increase the harvested energy from 2.2 µW/cm2 in the case of the harvesting thermal energy to 1.47 mW/cm2 in the case of harvesting both thermal energy and mechanical energy

Lead sulfide colloidal quantum dot photovoltaic cell for energy harvesting from human body thermal radiation

In this paper, we present the development of a solution-processed photovoltaic structure designed to convert human body thermal radiation into electricity. An active layer composed of a layer of isopropylamine-capped lead sulfide (PbS) quantum dots (QDs) covered with a layer of lithium chloride (LiCl) on top is sandwiched between a substrate and an aluminum contact. Experimental measurements reveal that the device was sensitive to infrared radiation with energies lower than the optical bandgap energy of the incorporated nanocrystals (Eg = 1.26 eV), allowing one to harvest thermal radiation from a human body. We used a conceptually different approach to harvest this radiation by intentionally introducing mid-gap states to the lead sulfide quantum dots through passivation with isopropylamine and likely enabling a multi-step photon absorption mechanism

The effect of isopropylamine-capped PbS quantum dots on infrared photodetectors and photovoltaics

In this paper, we explore the impact of isopropylamine (IPAM) as a short ligand on a solution-processed infrared photodetector and a photovoltaic device using lead sulfide (PbS) colloidal quantum dots. Original oleic acid capping is replaced by isopropylamine through a solution-phase ligand exchange process. Then a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] or MEH-PPV and the isopropylamine-capped PbS colloidal quantum dots is prepared for a photosensitive layer sandwiched by two different electrodes. Results illustrate that contribution of isopropylamine can improve the responsivity of a photodetector and enhance the photovoltaic performance by increasing the open circuit voltage and short circuit current

A Wearable Pulse Oximeter With Wireless Communication and Motion Artifact Tailoring for Continuous Use

Advances in several engineering fields have led to a trend toward miniaturization and portability of wearable biosensing devices, which used to be confined to large tools and clinical settings. Various systems to continuously measure electrophysiological activity through electrical and optical methods are one category of such devices. Being wearable and intended for prolonged use, the amount of noise introduced on sensors by movement remains a challenge and requires further optimization. User movement causes motion artifacts that alter the overall quality of the signals obtained, hence corrupting the resulting measurements. This paper introduces a fully wearable optical biosensing system to continuously measure pulse oximetry and heart rate, utilizing a reflectance-based probe. Furthermore, a novel data-dependent motion artifact tailoring algorithm is implemented to eliminate noisy data due to the motion artifact and measure oxygenation level with high accuracy in real time. By taking advantages of current wireless transmission and signal processing technologies, the developed wearable photoplethysmography device successfully captures the measured signals and sends them wirelessly to a mobile device for signal processing in real time. After applying motion artifact tailoring, evaluating accuracy with a continuous clinical device, the blood oxygenation measurements obtained from our system yielded an accuracy of at least 98%, when compared to a range of 93.6%-96.7% observed before from the same initial data. Additionally, heart rate accuracy above 97% was achieved. Motion artifact tailoring and removal in real time, continuous systems will allow wearable devices to be truly wearable and a reliable electrophysiological monitoring and diagnostics tool for everyday use