Improvement of Cu₂ZnSn(S,Se)₄ solar cell efficiency by surface treatment

Abstract

Surface treatments for the purpose of contamination elimination and surface passivation were performed to as‐deposited CZTSSe thin films before CdS buffer layer deposition. It was found that HCl etching treatment removes contaminations such as sulfide and oxide on CZTSSe surface and helps enhancement of thiourea treatment carried out after HCl etching. Thiourea treatment drastically improves solar cell characteristics, especially FF and JSC, and it would have the effect of surface passivation, although surface sulfuration does not occur. The improvement of characteristics seems to be due to improvement of the film quality and increase in the width of a depletion layer. As a result, conversion efficiency of CZTSSe solar cells was improved from 6.3% to 10.3% with sequential treatment of HCl etching and thiourea treatment. 10.5% was achieved by air anneal after fabrication with both treatments.

Room‐Temperature Surface Sulfurization for High‐Performance Kesterite CZTSe Solar Cells

“…The EQE responses of these solar cells with AS vapor treatment are all enhanced in the wavelength region of 500–1100 nm, which is made possible by the reduction of the surface defects of the absorber treated with AS vapor. The surface sulfurization passivates the absorber surface, thus leading to the improvement of CdS/CZTSSe interface properties . However, oxide compounds at the CZTSe surface prevent AS vapor from diffusing into the film.…”

Is the Cu/Zn Disorder the Main Culprit for the Voltage Deficit in Kesterite Solar Cells?

“…[ 12 ] This critical process step was performed prior to the deposition of the CdS fi lm, by i) annealing the active layer in air (375 °C for 2 min) in order to oxidize the metal rich interfaces, and ii) applying a NH 4 OH-based wet etch (5 min dip in 7% aqueous NH 4 OH solution) to remove the newly created metal oxides (except SnO x ). In a similar way, a 30 min air annealing at wileyonlinelibrary.com 150 °C, followed by a wet aqueous chemical cleaning (thiourea and/or HCl dip), was found necessary for Furuta et al [ 23 ] to reach >10.5% effi cient devices (without ARC). This intentional oxidation appears quite similar to the one previously advocated by Repins et al which allowed them to achieve 9.15% with coevaporated CZTSe absorbers fabricated with a very Zn-rich terminated surface.…”

Influence of alkali metals (Na, Li, Rb) on the performance of electrostatic spray-assisted vapor deposited Cu2ZnSn(S,Se)4 solar cells

“…12. As suggested by Furuta et al the improvement of the characteristics seems to be due to improvement of the film quality and increase in the width of a depletion layer12. The latter assumption is demonstrated by the augmentation of the short-circuit current in the comparison between the same solar cells with and without HCl and thiourea treatment (Figs 2 and 3).…”

“…12. As suggested by Furuta et al the improvement of the characteristics seems to be due to improvement of the film quality and increase in the width of a depletion layer12.…”

“…Details on this techniques were described in ref. 12. A statistical study of light PV characteristics was performed on more than 25 cells with different alkali contents.…”