The cells of Graetzel (name of the inventor of the federal Polytechnic school of Lausanne) are nano-crystalline solar cells with dye. The heat strength was the weak point but been the subject of intensive research.

These cells are inspired by the Photosynthèse and consist of a side of a layer of Dioxyde of Titane covered with a dye called “ sensitizer ” and other of an electrolytic solution . When a luminous ray falls on the coloring one, a electron is ejected. All the electrons thus released cross oxide, are collected at the edge of the cell and then directed towards an external circuit.