Perovskite PV-powered RFID enables lowcost self-powered IoT sensors

Perovskite PV-powered RFID enables lowcost self-powered IoT sensors


MIT researchers have designed low-cost, photovoltaic-powered
sensors on RFID tags that work in sunlight and dimmer indoor lighting, and can transmit
data for years before needing replacement. By 2025, experts estimate the number of “internet
of things” devices — including sensors that gather real-time data about infrastructure
and the environment — could rise to 75 billion worldwide. As it stands, however, those sensors require
batteries that must be replaced frequently, which can be problematic for long-term monitoring. MIT researchers have designed photovoltaic-powered
sensors that could potentially transmit data for years before they need to be replaced. To do so, they mounted thin-film perovskite
cells as energy-harvesters on inexpensive radio-frequency identification (RFID) tags. Perovskite cells are known for their potential
low cost, flexibility, and relative ease of fabrication. The cells could power the sensors in both
bright sunlight and dimmer indoor conditions. Moreover, the team found the solar power actually
gives the sensors a major power boost that enables greater data-transmission distances
and the ability to integrate multiple sensors onto a single RFID tag. Depending on certain factors in their environment,
such as moisture and heat, the sensors can be left inside or outside for months or, potentially,
years at a time before they degrade enough to require replacement. That can be valuable for any application requiring
long-term sensing, indoors and outdoors, including tracking cargo in supply chains, monitoring
soil, and monitoring the energy used by equipment in buildings and homes. In recent attempts to create self-powered
sensors, other researchers have used solar cells as energy sources for internet of things
(IoT) devices. But those are basically shrunken-down versions
of traditional solar cells — not perovskite. The traditional cells can be efficient, long-lasting,
and powerful under certain conditions ,but are really infeasible for ubiquitous IoT sensors. Traditional solar cells are bulky and expensive
to manufacture, plus they are inflexible and cannot be made transparent, which can be useful
for temperature-monitoring sensors placed on windows and car windshields. They’re also really only designed to efficiently
harvest energy from powerful sunlight, not low indoor light. Perovskite cells, on the other hand, can be
printed using easy roll-to-roll manufacturing techniques for a few cents each; made thin,
flexible, and transparent; and tuned to harvest energy from any kind of indoor and outdoor
lighting. The idea, then, was combining a low-cost power
source with low-cost RFID tags, which are battery-free stickers used to monitor billions
of products worldwide. The stickers are equipped with tiny, ultra-high-frequency
antennas that each cost around three to five cents to make. RFID tags rely on a communication technique
called “backscatter,” that transmits data by reflecting modulated wireless signals off
the tag and back to a reader. A wireless device called a reader — basically
similar to a Wi-Fi router — pings the tag, which powers up and backscatters a unique
signal containing information about the product it’s stuck to. Traditionally, the tags harvest a little of
the radio-frequency energy sent by the reader to power up a little chip inside that stores
data, and uses the remaining energy to modulate the returning signal. But that amounts to only a few microwatts
of power, which limits their communication range to less than a meter. The MIT researchers’ sensor consists of
an RFID tag built on a plastic substrate. Directly connected to an integrated circuit
on the tag is an array of perovskite solar cells. As with traditional systems, a reader sweeps
the room, and each tag responds. But instead of using energy from the reader,
it draws harvested energy from the perovskite cell to power up its circuit and send data
by backscattering RF signals. The key innovations are in the customized
cells. They’re fabricated in layers, with perovskite
material sandwiched between an electrode, cathode, and special electron-transport layer
materials. This achieved about 10 percent efficiency,
which is fairly high for still-experimental perovskite cells.

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