Principle of Work of Solar Cell or Photovoltaic Cell

Tsohon kimi da tsarin jiki a kan layi na jiki shi da yin abu a cikin wani alamar 'yan adadin kimi da ya fara ne a cikin jiki. Idan an yanke mutanen jiki da sauran kayayyakin jiki, yawancin 'yan adadin kimi suna zama a cikin jiki. Wannan shine babban sabbin tsohon jiki da tsarin jiki. Jiki photovoltaic shine babban yankin na sistem din da ake amfani da ita don samun jiki daga layi. Silicon shine mafi yawan kayayyaki da ake amfani da ita don gina jiki photovoltaic. Atomin silicon ta da 'yan adadi biyu. A cikin kayan kristal, har zuwa silicon ta yi sharhi a binciken har zuwa silicon na musamman don samun hububucewar covalent bayan su. Haka ce silicon kristal ta sami tasirin lattice tetrahedral. Idan layi ke yanke wani abu, wata batu a layi ce ke rarrabe, wata batu ke tafara a cikin abu, sannan kare batu ke yanke abu.

Wannan ba shi ne idan layi ke yanke kristal silicon. Idan ingancin layi ke da kyau, yawancin 'yan adadin kimi suna zama a cikin kristal, sannan 'yan adadin kimi suna rage 'yan adadin covalent. Wadannan 'yan adadin rage suna samu karfin da za su iya haɗa daga bandin valence zuwa bandin conduction. Saboda haka, suna rage daga hububucewar covalent, akwai fage a cikin hububuce. Wadannan suna nufin 'yan adadin free electrons suna tafiya daidai a cikin tasirin kristal silicon. Wadannan 'yan adadin free electrons da fagen suna da muhimmanci a kan samun jiki a jiki photovoltaic. Wadannan 'yan adadin da fagen suna nufin 'yan adadin kimi da fagen da ma rayuwa ba. Wadannan 'yan adadin kimi da fagen ba su iya samun jiki a cikin kristal silicon bakwai. Yana buƙata wani yanayin da ya kunshi don haka.

Idan an yanke impurity pentavalent kamar phosphorus zuwa silicon, 'yan adadin valence biyar zuwa phosphorus suna sharhi a binciken har zuwa zuwa silicon na musamman, sannan 'yan adadin valence biyu ba su iya samun hububucewar covalent ba.

Wannan 'yan adadin biyu suna zama mai yiwuwa a kan atomin. Idan an yi a cikin gida, karfin thermal wanda ake samu a cikin kristal ya fi yawa da za su rage 'yan adadin biyu zuwa atomin. Idan 'yan adadin biyu su rage, atomin phosphorus suna zama ions positive immobile. Wadannan 'yan adadin rage suna zama free electrons, amma ban da fagen ko hububucewar covalent da za su rage. Wadannan 'yan adadin free electrons suna da yin yin da za su samun current a cikin semiconductor. Duk da yake da 'yan adadin free electrons, amma abu suna da yin neutral saboda yadda adadin ions positive phosphorus wanda ake kula a cikin kristal ke da yin yin da 'yan adadin free electrons. Yanayin da ake amfani da impurities a cikin semiconductor shine doping, sannan impurities suna nufin dopants. Dopants pentavalent wanda su rage 'yan adadin free electrons suna nufin donors. Semiconductors wanda ake amfani da dopants donors suna nufin n-type ko negative type semiconductor saboda yake da 'yan adadin free electrons da suke da yin negative charge.

Idan an yanke impurity trivalent kamar boron zuwa kristal semiconductor, wace batu a cikin semiconductor zai zama. A wannan lokacin, yawancin atoms silicon a cikin kristal lattice zai zama boron, yana nufin boron atoms zai zama mata masu silicon a cikin tasirin lattice. 'Yan adadin valence uku zuwa boron atom suna sharhi a binciken har zuwa 'yan adadin valence uku zuwa neighbour silicon atoms don samun hububucewar covalent uku. Don wannan tasirin, za a bai atom silicon wanda yake da boron atom, 'yan adadin valence biyu ba su iya samun hububucewar covalent biyu ba. Saboda haka, 'yan adadin valence biyu zuwa silicon atoms suna zama unpaired da ya nuna hububucewar incomplete. Saboda haka, za a bai lack of one electron a cikin hububucewar incomplete, da ya nuna hububucewar incomplete zai ragewar 'yan adadin kimi don ya tabbatar.

Wannan vacancy shine conceptually nufin hole positive. A cikin semiconductor wanda ake amfani da impurity trivalent, yawancin hububucewar covalent suna rage don samun hububucewar incomplete. Idan wata hububuce rage, wata hole zai zama a cikin ita. Idan wata hububuce complete, hole a cikin ita zai zama. Haka ce, wata hole zai zama a nan, wata hole zai zama a nan. Saboda haka, holes suna tafiya daidai a cikin kristal semiconductor. Saboda haka, holes suna tafiya daidai kamar 'yan adadin free electrons a cikin kristal semiconductor. Saboda har zuwa holes zai iya rage 'yan adadin kimi, impurities trivalent suna nufin acceptor dopants, sannan semiconductors wanda ake amfani da acceptor dopants suna nufin p-type ko positive type semiconductor.

A cikin n-type semiconductor, 'yan adadin free electrons suna da yin negative charge, sannan a cikin p-type semiconductor, holes suna da yin positive charge, saboda haka, 'yan adadin free electrons a cikin n-type semiconductor da holes a cikin p-type semiconductor suna nufin majority carrier a cikin n-type semiconductor da p-type semiconductor respectively.

Yana da potential barrier a nan bayan n-type da p-type material. Wannan potential barrier shine muhimmi ga aiki a cikin photovoltaic ko solar cell. Idan n-type semiconductor da p-type semiconductor suna yanke, 'yan adadin free electrons near to the contact surface of n-type semiconductor suna rage da adjacent holes of p-type material. Saboda haka, 'yan adadin free electrons a cikin n-type semiconductor near to its contact surface suna rage zuwa adjacent holes of p-type material. Ba 'yan adadin free electrons ba, 'yan adadin valence of n-type material near the contact surface suna rage daga hububucewar covalent da rage zuwa nearby holes in the p-type semiconductor. Saboda haka, za a bai number of holes created in the n-type material near the contact surface. Saboda haka, holes in the p-type materials near the contact zone suna rage due to recombination, sannan holes suna zama a cikin n-type material near same contact zone. Wannan shine equivalent to the migration of holes from p-type to the n-type semiconductor. Saboda haka, idan an yanke n-type semiconductor da p-type semiconductor, 'yan adadin kimi suna rage zuwa p-type da holes suna rage zuwa n-type. Wannan process shine tafiye, amma ba za su duba da yawa. Ba da yake, za a bai layer of negative charge (excess electrons) in the p-type semiconductor adjacent to the contact along the contact surface. Kamar haka, za a bai layer of positive charge (positive ions) in the n-type semiconductor adjacent to contact along the contact surface. Thickness of these negative and positive charge layers yana ci gaba, amma ba za su duba da yawa. Saboda haka, ba za su rage 'yan adadin kimi zuwa p-type semiconductor. Saboda haka, holes ba za su rage zuwa n-type semiconductor. Holes suna rage zuwa negative layer in p-type semiconductor, sannan suna rage zuwa 'yan adadin kimi, sannan ba za su rage zuwa n-type region.

Ba tare, negative charge layer in the p-type side and positive charge layer in n-type side together form a barrier which opposes migration of charge carriers from its one side to other. Kamar haka, holes in the p-type region are held back from entering the n-type region. Due to positive and negative charged layer, there will be an electric field across the region and this region is called depletion layer.

Idan layi ke yanke kristal, wata batu a layi ce ke yanke kristal, sannan 'yan adadin valence suna rage zuwa 'yan adadin free electrons da holes.

Idan layi ke yanke n-type semiconductor, 'yan adadin kimi daga light-generated electron-hole pairs ba su iya rage zuwa p-region saboda ba su iya rage across the potential barrier due to the repulsion of an electric field across depletion layer. Ba tare, light-generated holes suna rage zuwa depletion region due to the attraction of electric field of depletion layer where they recombine with electrons, and then the lack of electrons here is compensated by valence electrons of p-region, and this makes as many numbers of holes in the p-region. As such light generated holes are shifted to the p-region where they are trapped because once they come to the p-region cannot be able to come back to n-type region due to the repulsion of potential barrier.

As the negative charge (light generated electrons) is trapped in one side and positive charge (light generated holes) is trapped in opposite side of a cell, there will be a potential difference between these two sides of the cell. This potential difference is typically 0.5 V. This is how a photovoltaic cells or solar cells produce potential difference.

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