1 research outputs found
Potassium Postdeposition Treatment-Induced Band Gap Widening at Cu(In,Ga)Se<sub>2</sub> Surfaces – Reason for Performance Leap?
Direct and inverse photoemission
were used to study the impact
of alkali fluoride postdeposition treatments on the chemical and electronic
surface structure of CuÂ(In,Ga)ÂSe<sub>2</sub> (CIGSe) thin films used
for high-efficiency flexible solar cells. We find a large surface
band gap (E<sub>g</sub><sup>Surf</sup>, up to 2.52 eV) for a NaF/KF-postdeposition
treated (PDT) absorber significantly increases compared to the CIGSe
bulk band gap and to the E<sub>g</sub><sup>Surf</sup> of 1.61 eV found
for an absorber treated with NaF only. Both the valence band maximum
(VBM) and the conduction band minimum shift away from the Fermi level.
Depth-dependent photoemission measurements reveal that the VBM decreases
with increasing surface sensitivity for both samples; this effect
is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic
structure changes can be linked to the recent breakthroughs in CIGSe
device efficiencies