The number of sensors in the Internet of Things (IoT) is about to grow from billions to trillions. As most of them will be connected wirelessly, and the capacity for batteries as a power solution is limited, eyes turn towards other energy harvesting solutions.
Vibrations from equipment, natural or artificial light, temperature differences and radio-frequency and WiFi waves can all be exploited to power the small and low-power devices that monitor our surroundings. Many innovative energy harvesting technologies are being developed at research institutions around the world and step by step make their way into our everyday lives.
The Promise of Light Harvesting
Among energy harvesting options, light-harvesting has been upheld as reliable and dependable. Light-Harvesting can produce relatively sizeable amounts of energy consistently and predictably.
Photovoltaic technology has also been used for a long time to power smaller devices. Silicon-based systems are the most implemented technology, due to its maturity, affordability, stability, and safety. Cheap manufacturing in China has made it widely implemented for power production. Still, silicon cells cannot meet the demands of IoT systems; the cells are heavy, require strong illumination at a specific angle to function well, and they are black and inflexible.
The Printing Revolution
In 2007 a pioneering work on the use of inkjet printing technology for the fabrication of organic photovoltaics was published, which was subsequently adapted to fabricate thin-film (e.g. CIGS), dye-sensitized and perovskite solar cells. This was a revolutionary shift in how light could be used to produce electricity.
The new printing technology made the production cheap and flexible and reduced both wastes of materials and energy consumption. The cells could be made thin and light-weight, in flexible materials and a variety of colors and opacity shades. They could also be printed directly onto surfaces of different kinds – such as the surface of an IoT sensor.
Yet, as is often the case with new technologies, even as the printed cells were spectacularly overcoming so many of the limitations of silicon, they struggled to live up to some of the more basic criteria. Some are made with toxic materials that are unsuitable for home environments, and many that show promise in the lab turn out to be unstable over time in real conditions – because they cannot deal with variable temperatures, for example, or with moisture.
An ironic twist is that while many printed cells perform remarkably well in low light, they degrade under exposure to UV light and so cannot be used anywhere that natural light occurs. Additional issues of scalability and remaining limitations of aesthetic design add to why many of the new printed cells have struggled to reach for implementation beyond the laboratories and a handful of pilot installations.
A New Generation of Printing
Despite these setbacks, printed solar cells hold much promise for the future. We all know it takes time for new technologies to mature. Over a decade since printed photovoltaics were first introduced, things are looking up: printers are getting cheaper each year and also more precise, inks formulations for advanced material printers are developing to new levels and the knowledge of curing techniques – the post-processing of advanced prints – is expanding.
Those who develop advanced printing today no longer have to start from scratch; there is a wealth of know-how and experience to build on. The latest technologies build on the benefits of printing without compromising safety, sustainability or functionality, and reach new levels of design capabilities.
It is unlikely that one technology will be the answer to all situations. In new buildings, it often makes sense to integrate sensors into the wired electricity grid, but that is not a viable option for retrofitting existing buildings.
Wherever silicon solar cells can do the job, they will probably be the choice for the foreseeable future. But the next generation of printed solar cells could bring the implementation of IoT in buildings to a new level, reaching far beyond just new building production and prestige installations.