This little cube is made out of solar cells bought on eBay and they belong to
a satellite called Symphonie launched in 1974, and was the first European Space Communications joint venture.
In 1983, Symphonie reached terminal orbit and was deactivated.
The solar photovoltaic cells continue to "live" in that, within a very thin layer of silicon, their chemical transformation of light into energy continues to happen even today.
This low amount of energy is, however, quickly dissipated around the cube and therefore useless.