3. Light and elevated temperature degradation

Light and temperature changes can also induce some degradation in the solar cell materials. For example, in the case of amorphous silicon, the inclusion of about 10% hydrogen (a-Si:H) serves to saturate many of the dangling bonds. Figure 9 shows schematically the atomic structure of a-Si:H material. With it, the density of states in the forbidden gap is drastically reduced, and the material can be doped. However, the saturation of dangling bonds with hydrogen is not totally stable. During illumination, the bonds are again broken due to recombination or photon absorption. This property, known as the Staebler–Wronski effect,...