Fundamental limits on optical transparency of transparent conducting oxides: Free-carrier absorption in SnO2

Transparent conducting oxides combine high electrical conductivity with transparency to visible light. However, the large concentration of free electrons introduces a source of absorption that limits the transparency. Here, we evaluate the importance of phonon-assisted free-carrier absorption in SnO2 completely from first principles. Our results show that absorption is modest in the visible and much stronger in the UV and infrared. We also provide insight into the mechanisms that govern absorption in different wavelength regimes.