Solar cell (image 3 of 3). Computer illustration of a solar cell discharging. Solar cells convert sunlight into electricity. This cell has 2 layers of silicon (Si, upper & lower left). The top layer also contains phosphorous (P) atoms. Atoms are seen as purple balls. P normally holds 5 outer electrons (e-, blue), while Si holds 4. Sunlight on the top layer releases e- whose places around the P atom are taken by e- from the bottom layer. The e- build-up in the top layer is being dischar- ged as an electric current, lighting up the bulb. For the solar cell's structure and for it charging see images T155/108 and T155/109 respectively.