Effect of a CIGS Absorption Layer on the Film Properties of Molybdenum Back Contact

Molybdenum (Mo) thin films are used widely as the back contact of Cu(In,Ga)Se₂ (CIGS)-based solar cells. This study examined the effects of an approximately 500 nm Mo/Mo bilayer deposited under different working pressures on the structural properties of a subsequently co-evaporated CIGS absorber layer. The Mo first bottom layer with a 100 to 400 nm thickness was deposited at higher working pressures (10 mTorr). Subsequently, a second top layer with a total thickness of approximately 500 nm was formed under a lower working pressure (3 mTorr). GD-MS analysis revealed Na diffusion in the resulting CIGS films. The effects of the Na doping on the structure and properties of CIGS films were examined. The (1 1 2) preferred orientation was enhanced by the addition of Na, indicating a better crystalline structure with Na doping. On the other hand, the crystallinity of the CIGS films decreased with increasing Mo first bottom layer thickness because of the excessive Na doping.