Determination of activation barriers for the diffusion of sodium through CIGS thin‐film solar cells

Abstract

We have determined the activation energies of sodium diffusion from the soda-lime glass substrate through the Mo back-contact layer, as well as through copper indium gallium diselenide (CIGS) deposited on the Mo back-contact layer of CIGS thin-film solar cells. The activation energies were determined by X-ray photoelectron spectroscopy (XPS) to measure surface sodium concentrations before and after thermally induced diffusion. The activation energies were found to be similar for the diffusion of Na through the Mo/glass and CIGS/Mo/glass thin films, approximately 8Á6 and 9Á6 kcal/mol, respectively. Furthermore, the sodium diffusion was found to occur by annealing in an environment of 1Á0 Â 10 À5 Torr of air, oxygen, or water vapor, but not in vacuum of less than 1 Â 10 À8 Torr. In addition, the diffusion of Na was found to occur faster in the presence of oxygen than in water under identical annealing conditions.

First‐principles study on alkali‐metal effect of Li, Na, and K in Cu2ZnSnS4 and Cu2ZnSnSe4

“…The migration enegy of (Na Cu →V Cu ) in CIS (0.31eV) agrees with the recently reported value (0.35 eV) by Oikkonen et al [5]. Our calculated migration energy of (Na Cu →V Cu ) in CIS is also consistent with the experimental results [21][22][23]. Zellner et al reported the activation energy of Na diffusion through the CIGS layer of 0.37 eV by XPS measurements [21].…”

The importance of back contact modification in Cu2ZnSnSe4 solar cells: The role of a thin MoO2 layer

“…reported a reduction in the activation energy for Na diffusion by air annealing, supporting the idea of Na diffusion assisted by oxygen presence [65]. It has been also suggested that Mo-O species can enhance Na diffusion via solubility of Na, i.e.…”

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

“…Each CIGSe series consisted of four samples with different NaF precursor thickness. The nominal thicknesses of the NaF precursors are 0 (Na-free samples), 8,16, and 32 nm. In addition, CIGSe reference samples for the Cu-rich and Cu-poor process deposited on soda-lime glass were prepared for bulk composition and thickness measurements performed by xray fluorescence analysis (XRF) using a Philips MagiXPro PW 2400 spectrometer.…”

“…4 In comparison high-efficiency devices on soda-lime glass substrates are typically obtained using growth temperatures of $550 C. Furthermore, it is well known that in a conventional sodalime glass substrate based CIGSe solar cell structure, Na from the soda-lime glass substrate diffuses into the absorber layer due to the elevated temperature during CIGSe formation. [5][6][7][8] Na incorporation into the CIGSe absorber results in a significant improvement of solar cell efficiency, [9][10][11][12] and so for devices based on alternative (i.e., Na-free) substrates, Na must be added deliberately as part of the solar cell manufacturing process. Na can be incorporated prior to, 13,14 during, 12,15 or after 2,16 CIGSe growth.…”