The emergence of modern technologies, such as Wireless Sensor Networks (WSNs), the Internet-of-Things (IoT), and Machine-to-Machine (M2M) communications, involves the use of batteries, which pose a serious environmental risk, with billions of batteries disposed of every year. However, the combination of sensors and wireless communication devices is extremely power-hungry. Energy Harvesting (EH) is fundamental in enabling the use of low-power electronic devices that derive their energy from external sources, such as Microbial Fuel Cells (MFC), solar power, thermal and kinetic energy, among others. Plant Microbial Fuel Cell (PMFC) is a prominent clean energy source and a step towards the development of self-powered systems in indoor and outdoor environments. One of the main challenges with PMFCs is the dynamic power supply, dynamic charging rates and low-energy supply. In this paper, a PMFC-based energy harvester system is proposed for the implementation of autonomous self-powered sensor nodes with IoT and cloud-based service communication protocols. The PMFC design is specifically adapted with the proposed EH circuit for the implementation of IoT-WSN based applications. The PMFC-EH system has a maximum power point at 0.71 V, a current density of 5 mA cm − 2 , and a power density of 3.5 mW cm − 2 with a single plant. Considering a sensor node with a current consumption of 0.35 mA, the PMFC-EH green energy system allows a power autonomy for real-time data processing of IoT-based low-power WSN systems.

Inverted organic cells are promising devices for sustainable and low-cost future electric generation. In this work, we present the degradation mechanisms studied in ITO/TiO 2 /PTB7:PC 70 BM/V 2 O 5 /Ag inverted organic solar cells (iOSCs) by impedance spectroscopy (IS). Measurements were performed on encapsulated (controlled environment) and nonencapsulated (ambient condition) cells following their temporal evolution under AM1.5 illumination for several voltage biases. From the impedance spectra, analyzed in terms of resistive/capacitive equivalent circuits, we were able to identify that the most sensitive layers inside of the device are contact layers. According with presented, IS technique is useful for determining the materials that have more influence on the degradation of organic solar cells. We demonstrate that IS is a powerful technique to identify the limiting mechanisms and to establish the limiting materials inside of the iOSCs.

In this paper, we demonstrate that zinc oxide (ZnO) layers deposited by inkjet printing (IJP) can be successfully applied to the low-temperature fabrication of efficient inverted polymer solar cells (i-PSCs).

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Long power wide area networks (LPWAN) systems play an important role in monitoring environmental conditions for smart cities applications. With the development of Internet of Things (IoT), wireless sensor networks (WSN), and energy harvesting devices, ultra-low power sensor nodes (SNs) are able to collect and monitor the information for environmental protection, urban planning, and risk prevention. This paper presents a WSN of self-powered IoT SNs energetically autonomous using Plant Microbial Fuel Cells (PMFCs). An energy harvesting device has been adapted with the PMFC to enable a batteryless operation of the SN providing power supply to the sensor network. The low-power communication feature of the SN network is used to monitor the environmental data with a dynamic power management strategy successfully designed for the PMFC-based LoRa sensor node. Environmental data of ozone (O3) and carbon dioxide (CO2) are monitored in real time through a web application providing IoT cloud services with security and privacy protocols.

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