Low-temperature growth of Na doped CIGS films on flexible polymer substrates by pulsed laser ablation from a Na containing target

Femtosecond pulsed laser deposition (fs-PLD) was investigated to grow Cu(In,Ga)Se2 (CIGS) films at low temperature (≤ 300 °C), which allowed the use of flexible polymer substrates such as polyimide (PI). X-ray diffraction showed that the films grown on the PI substrates had a pure chalcopyrite phase with a preferred (112) orientation. Because the CIGS films grown on the soda–lime glass substrates were known to have the improved photoelectrical properties owing to the Na diffusion from the substrates, in view of the absence of Na in the polymer substrates, we tried to dope the CIGS films intentionally by adding Na into the fs-PLD targets. The CIGS:Na targets were successfully synthesized from the Cu, In, Ga, Se and NaF powders by the solid state reaction. The results showed that the addition of 5 at.% Na in the target did not change the fs-PLD growth parameters notably and well crystallized CIGS:Na films could be grown on the PI substrates, which showed an increased carrier concentration and conductivity.