Harvesting energy directly from sunlight using photovoltaic (PV) technology is well recognized as an essential component for the future global energy requirements. PV based devices are nowadays considered to be economically competitive on par with the other fossil fuels or renewable energy technologies. In addition, the large-scale production of these devices (as a sustainable energy source) could help us to meet a signifi cant portion of our daily energy requirements. These devices were extensively studied since 1950s, when the fi rst crystalline silicon solar cell (effi ciency 6%) was developed at Bell Laboratories . Over these years, solar cells have been made from many other semiconducting materials with various device confi gurations such as singlecrystal, polycrystalline, and amorphous thin-fi lm structures .