| Abstract [eng] |
For a last few decades of the 20 century, a huge interest in solar cells has been started and it continues until today. The reason of that is decrease of traditional energy resources and intention of goverments to limit pollution and global warming. Semiconductor solar cells made of crystaline silicon were always the most useful and popular among solar cells. However, heating of carriers, when solar energy is unused to generate pairs of carriers, limits efficiency of Si cells to 25%. They are called hot carriers and are observed as negative voltage in investigations of solar cells. Also, generation of carriers induce a photoelectromotive force with opposite polarity than voltage of hot carriers. Both of these values appear when pn junction is under intense laser illumination. Therefore it is topical interest to find the ways not only reducing the negative impact of the hot carriers, but also using hot carriers for efficient solar cell operation. The aim of this master work is to investigate the influence of hot carriers on the photovoltage formation across GaAs and Si pn junction under intense illumination. This work includes a literature review and an investigation of hot carriers electromotive force and photoemf dependance on various powers and wavelengths of radiation. Methods to investigate solar cells in nitrogen temperatures and under various external voltages are also created. Lastly, the results and conclusions are discussed. It was found that hot carriers electromotive force is caused by light heating the carriers in pn junction. Photovoltage was observed when light generated pairs of electrons and holes. It was noticed that applied external reverse-biased voltage increases photovoltage influenced of carriers generation, while forward-biased external voltage diminishes it. In hot carriers case, it is opposite. Reverse-biased external voltage makes hot carriers emf to diminish, while forward-biased voltage forces it to increase. |
