Inverted solar cell is based on steam engine theory

In 1824, physicist Sadi Carnot concluded that a steam engine works because heat always flows towards cold, and that heat flow is converted into motion. In a steam engine the heat makes vapour expand, causing a piston to move, with the steam giving off heat again in the process.

The principle can be transferred to any machine that works due to temperature differences. In an petrol engine, motion is produced when air heated in petrol combustion expands to push a piston. The heat can also make electrons move, and that is the process scientists are using in the newly-developed inverted solar cell.

Heat will always flow towards cold, and the heat causes motion en route. Warm container Piston Steam Piston Cold container