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Staebler Wronski Effect

When light strikes on hydrogenated amorphous silicon it exhibits a metastable change in the photovoltaic properties. When hydrogenated amorphous silicon is exposed prolonged to the light its efficiency to produce electricity decreases that is called Staebler Wronski Effect. This degradation of the electrical output of hydrogenated amorphous silicon is due to prolonged illumination. David L. Staebler and Christopher R. Wronski discovered this fact in 1977. The intensity of degradation depends on the diffusion coefficient of hydrogen and local bonding formation promoted by hydrogen.

Explanation of Staebler-Wronski Effect

The Stabler Wronski theory suggested that when intense light falls on hydrogenated amorphous silicon, the electron-hole pairs are created which again combine with neighboring Si-Si bonds that have weak foundation. During recombination process the tremendous amount of energy is released which creates defects and causes degradation noncrystalline structure of the hydrogenated amorphous silicon. The recombinations occur especially in those regions where the band edges are very close to one another energetically and also have the smaller concentration of hydrogen. The breakage leads to enhanced hydrogen diffusion, and the creation of dangling bonds (H atom then forms a new bond with neighboring Si atom), and this reduces the flow of current by tapping electron-hole pairs. The movement of hydrogen atoms is responsible for the creation of dangling bonds. This phenomenon in hydrogenated amorphous silicon reduces the conversion of light energy into electrical energy. The Staebler Wronski effect reduces the efficiency of solar cell up to 15 % within the first 1,000 Hrs. dangling bonds

Factors which affects Staebler-Wronski Effect

Methods to Overcome Staebler-Wronski Effect

Paramagnetic Properties of Amorphous Silicon

The metastable defect of Amorphous Silicon shows paramagnetic properties that vary with respect to the microscopic environment. These defects of a-Si actually come in two types. One is uniformly distributed and other is concentrated in clusters within the internal surface of the cell during the manufacturing process. The clusters of defects are generated on the internal walls of microvoids which contribute to the light-induced degradation of amorphous silicon in the thin film solar cell. paramagnetic properties of amorphous silicon


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