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In physics, the Shockley–Queisser limit or detailed balance limit refers to the maximum theoretical efficiency of a solar cell using a p-n junction to collect power from the cell. It was first calculated by William Shockley and Hans Queisser at Shockley Semiconductor in 1961.〔William Shockley and Hans J. Queisser, ("Detailed Balance Limit of Efficiency of p-n Junction Solar Cells" ), ''Journal of Applied Physics'', Volume 32 (March 1961), pp. 510-519; 〕 The limit is one of the most fundamental to solar energy production, and is considered to be one of the most important contributions in the field.〔("Hans Queisser" ), Computer History Museum, 2004〕 The limit places maximum solar conversion efficiency around 33.7% assuming a single p-n junction with a band gap of 1.34 eV (using an AM 1.5 solar spectrum).〔 That is, of all the power contained in sunlight falling on an ideal solar cell (about 1000 W/m²), only 33.7% of that could ever be turned into electricity (337 W/m²). The most popular solar cell material, silicon, has a less favourable band gap of 1.1 eV, resulting in a maximum efficiency of 33.3%. Modern commercial mono-crystalline solar cells produce about 24% conversion efficiency, the losses due largely to practical concerns like reflection off the front surface and light blockage from the thin wires on its surface. The Shockley–Queisser limit only applies to cells with a single p-n junction; cells with multiple layers can outperform this limit. In the extreme, with an infinite number of layers, the corresponding limit is 86% using concentrated sunlight.〔A. De Vos, "Detailed balance limit of the efficiency of tandem solar cells", ''Journal of Physics D: Applied Physics'' Volume 13, Issue 5 (14 May 1980), page 839-846 〕 ==Background== In a traditional solid-state semiconductor such as silicon, a solar cell is made from two doped crystals, one an n-type semiconductor, which has extra free electrons, and the other a p-type semiconductor, which is lacking free electrons, referred to as "holes." When initially placed in contact with each other, some of the electrons in the n-type portion will flow into the p-type to "fill in" the missing electrons. Eventually enough will flow across the boundary to equalize the Fermi levels of the two materials. The result is a region at the interface, the p-n junction, where charge carriers are depleted and/or accumulated on each side of the interface. In silicon, this transfer of electrons produces a potential barrier of about 0.6 V to 0.7 V.〔(【引用サイトリンク】 publisher = specmat.com )〕 When the material is placed in the sun, photons from the sunlight can be absorbed in the p-type side of the semiconductor, causing electrons in the valence band to be promoted in energy to the conduction band. This process is known as photoexcitation. As the name implies, electrons in the conduction band are free to move about the semiconductor. When a load is placed across the cell as a whole, these electrons will flow from the p-type side into the n-type side, lose energy while moving through the external circuit, and then go back into the p-type material where they can re-combine with the valence-band holes they left behind. In this way, sunlight creates an electric current.〔 (The process is similar if the photons are absorbed in the n-type side of the semiconductor; the only difference is that instead of the photo-excited electrons flowing from the p-type side into the n-type side, the photo-excited holes flow from the n-type side into the p-type side. Both processes then involve electrons from the conduction band of the n-type side moving around the external circuit to recombine with the holes in the valence band of the p-type side.) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shockley–Queisser limit」の詳細全文を読む スポンサード リンク
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