. These bands allow two low energy photons to add up to one exciton and this is supposed to yield an efficiency of ~63% [9] and [10]. Another approach is impact or avalanche ionization. An electron with enough kinetic energy can knock a bound charge carrier from its bound state and make it free for conduction, thus creating an electron–hole pair. Thus, more than one pair per electron can be produced which shall lead to enhanced efficiency of a solar cell.