Simple solar cell

Organic thin-film solar cells in their most basic form consist of two layers of semiconducting materials between a transparent and reflecting electrode. Sunlight passes through the transparent electrode into the semiconductor donor material which has strong absorption bands for the solar spectrum. The other part is the electron accepting material, usually transparent to solar radiation.  The electrodes are normally a reflecting electrode and a transparent electrode used to collect electrical current.

Solar cells can consist of many different materials selected for a number of different reasons including matching the full spectrum of sunlight. Indium, Gallium materials in various compositions can be used to match the full spectrum of sunlight. The bandgaps of the materials used does matter, all direct bandgap semiconductors combine elements from group III of the periodic table, like aluminum, gallium, or indium, with elements from group V, like nitrogen, phosphorus, or arsenic. Three or more materials may be combined to create the most efficient multijunction solar cells with efficiencies in the 30+% range. The method of application of most of the materials is sputtering which seems to give the desired results for cost trade off issues.

Much of today’s research in multi-junction cells focused on Gallium Arsenide as one (or all) of the components. Many variations or mixtures of materials such as CIGS and Gallium Indium Phosphide are just two of the current materials being used. The tunnel junction is to aid in the flow of electrons between cell.