Fast chemical bath deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se2 solar cells

In order to decrease the deposition time of chemical bath deposited (CBD) Zn(O,S) buffer layers in CIGSe solar cell, the alternative CBD route using H2O2 as additional oxygen source has been investigated. The morphology and the optical properties of the Zn(O,S) thin films grown with and without additive have been compared through scanning electron microscopy (SEM) observations and UV-visible transmission T(λ) and reflectivity R(λ) measurements, respectively. It is observed that deposition time shorter than 5min is sufficient to achieve films with similar properties to those deposited following the standard recipe in 15min. The characteristics of CIGSe/Zn(O,S) structures for which the Zn(O,S) growth has been interrupted after different bath immersion durations have been investigated by XPS measurements. The evolution of the In3d and Zn2p3/2 signals reveals that after 2min of deposition, the Zn(O,S) layer grown by the alternative process completely covers the CIGSe and suggests that the increase of the Zn(O,S) growth rate is most probably due to the acceleration of cluster mechanism growth. A comparative study of devices buffered with the so-called fast and standard Zn(O,S) shows similar efficiencies in either case after light soaking.