Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se₂ thin film solar cells

Abstract

While the major function of molybdenum (Mo) back contact on soda‐lime glass (SLG) substrate in Cu(In,Ga)Se2 (CIGS) solar cells is to provide good adhesion and good conductivity, its role as the transportation channel for alkali elements from SLG substrate to CIGS layer has often been overlooked. In this work, we have intentionally fabricated tri‐layered structure in contrast to the conventional bi‐layered structure for Mo back contact with the microstructure of the thin topmost Mo layer manipulated by the Ar pressure and water vapor during sputtering deposition. It has been discovered that the CIGS solar cell conversion efficiency can be greatly affected by this thin topmost Mo layer of the back contact. Investigations on the elemental depth profiles in the CIGS devices and the chemical states of Mo on the back contact surfaces have revealed that the surface layer of Mo back contact has a strong effect on the diffusion of alkali elements from SLG into CIGS absorber layer, which in turn influences the formation of Ga gradient in the CIGS layer and thus the solar cell performance. It was revealed that Mo(OH)6 and MoO3 formed on the surface of Mo back contact play a key role in determining the K atom distribution and Ga gradient. A reaction mechanism was also proposed.

Scalable production of foam-like nickel–molybdenum coatings via plasma spraying as bifunctional electrocatalysts for water splitting

“…30 Here, we detected the doublets associated with metallic Mo 0+ (228.07 eV/231.22 eV, 3d 5/2 , 3d 3/2 ) and partially oxidized Mo with three distinct oxidation states such as Mo δ + (0 < δ < 4 : 229.09 eV/232.24 eV, 3d 5/2 , 3d 3/2 ), Mo 4+ (230.27 eV/233.42 eV, 3d 5/2 , 3d 3/2 ), and Mo 6+ (232.17 eV/235.32 eV, 3d 5/2 , 3d 3/2 ). 31–33 The XPS spectrum of O 1s presented in Fig. 5(d) reveals the presence of metal hydroxides seen as a peak at 531.5 eV, in agreement with the Ni spectra.…”

“…5 ), and Mo 6+ (232.17 eV/ 235.32 eV, 3d 5/2 , 3d 3/2 ). [31][32][33] The XPS spectrum of O 1s presented in Fig. 5(d) reveals the presence of metal hydroxides seen as a peak at 531.5 eV, in agreement with the Ni spectra.…”

Double-Sided Heat-Exchange CBD System for Homogeneous Zn(O,S) Thin Films in Highly Efficient CIGS Solar Devices

“…No metallic grids were used for modules. Note that the details mentioned above can be found in our previous works. ,− …”

Surface Engineering of Submicron Cu(In,Ga)Se2 for High-Efficient Zn(O,S)-Based Solar Cells with Lower Light Soaking Effects

“…The manufacturing process for CIGS thin-film solar cells adopted is similar to that described in our prior reports. − As the back electrode, an 800 nm thick Mo film was sputtered on soda-lime glass. And then, the three-step co-evaporation technique was employed for the production of the CIGS absorption layer with a thickness of about 970 nm.…”