Solar cells
The thin wafer at the heart of every solar panel, quietly turning sunlight into a flow of electrons.
What it is
A solar cell, or photovoltaic (PV) cell, is a thin slice of semiconductor, usually silicon, that produces electricity when light falls on it. A single cell makes only a small voltage, so dozens are wired together inside a panel.
How it works
Silicon is treated so that one layer has extra electrons and the other has a shortage. Where the two layers meet, an electric field forms. When a photon of sunlight is absorbed, it frees an electron, and that built-in field pushes it in one direction. Thin metal lines printed on the cell collect these electrons as a direct current (DC).
Not every photon can be used. Light with too little energy passes through, and light with too much wastes the extra as heat. This is the main reason a single silicon cell has a practical efficiency ceiling, and why researchers stack different materials in tandem cells.
Advantages and limitations
Advantages
- Proven over decades in the field
- Abundant raw material (silicon)
- Steadily rising efficiency and falling cost
Limitations
- Efficiency drops as cells heat up
- Fragile on their own; need glass and framing
- Manufacturing is energy-intensive
Current development
Most new cells use designs such as PERC, TOPCon or heterojunction that reduce energy losses at the surfaces. The next step change is expected from tandem cells that add a perovskite layer on top of silicon.
Further reading
- Solar cell (Wikipedia)Overview of how PV cells work and their history
- NREL best research-cell efficiency chartThe standard record of laboratory efficiency records