In the near future, when use our smartphones to control everything in our houses from lights and door locks to the refrigerator and toaster, what will power all the little devices and sensors that operate that Internet of Things?

"Solar" power harvested from indoor lamps, says a team led by researchers at Uppsala University in Sweden. They've developed new photovoltaic cells that can convert up to 34% of visible light from indoor sources into electricity.

They published the results of their research last month in an article in the journal Chemical Science.

Most IoT devices need to be autonomous, requiring neither battery replacement nor a connection to the electrical grid. The new cells, made from copper and other low-cost, nontoxic materials, use dyes sensitized to the light spectrum of fluorescent lamps and LEDs. That lets them harvest ambient indoor light with maximum efficiency.

"Knowing the spectra of these light sources makes it possible to tune special dyes to absorb indoor light," said Marina Freitag, leader of the research team and an assistant professor in chemistry at Uppsala. She was quoted in a university news release.

"While generating large amounts of energy, these indoor photovoltaics also maintain a high voltage under low light, which is important to power IoT devices."

An adaptive power management system detects the amount of light available, increasing the computational workload when it's plentiful and ramping down the device's energy consumption when the house is darker.

"Ambient light harvesters provide a new generation of self-powered and smart IoT devices powered by an energy source that is largely untapped," said Freitag. "The combination of high efficiency and low cost with nontoxic materials for indoor photovoltaics is of paramount importance to IoT sustainability."