Evolution of Cu(In,Ga)Se₂ surfaces under water immersion monitored by X‐ray photoelectron spectroscopy

Abstract

Funding information Agence Nationale de la Recherche: Programme d'Investissement d'Avenir-ANR-IEED Cu(In,Ga)Se 2 absorbers were immerged in deionized water for different times, and specific chemical evolutions were monitored thanks to X-ray photoemission spectroscopy. Cu(In,Ga)Se 2 related dissolution products were studied in water through induced coupled plasma optical emission spectroscopy. From those analyses, specific surface network disorganization was observed, with Cu migration towards the surface, leading to different kinetics of oxidation and dissolution for each element that could be quantified.

The influence of relative humidity upon Cu(In,Ga)Se2 thin-film surface chemistry: An X-ray photoelectron spectroscopy study

“…We previously described the behaviour of a CIGS surface fully immersed in water (continuum of water). 17 Various oxides were observed, as well as a surface network reorganization, mainly due to Cu migration, in agreement with the present results obtained at 60% RH. A similar behaviour was also observed on GaSe ultrathin layers with a direct relation between the percentage of relative humidity and oxide growth.…”

“…[13][14][15][16] We also proved that CIGS surfaces immersed in water go through a drastic crystal lattice reorganization, inducing the growth of In oxides and a progressive dissolution of Ga oxides, then Se oxides, and finally Cu ones. 17 To overcome this issue, separate ageings are performed on bare stoichiometric CIGS surfaces at two different relative humidities (60 ± 2 % and 20 ± 2 %, respectively) for more than 1000 hours. Knowing that the stoichiometry of the chalcopyrite layers impacts the air ageing process, 18 by using a stoichiometric CIGS absorber, the focus will only be on the influence of the relative humidity on the surface degradation, without any concern about the gradient effect.…”

Synergistic effect between molybdenum back contact and CIGS absorber in the degradation of solar cells

“…20 Pure CIGS degradation is usually described in the literature by diffusion mechanisms of copper 21 or sodium 17,20,22 and oxidation. 21,23 The performance loss of the CIGS layer was described in the literature as occurring due to the formation of shunting paths (through which the electrons produced in the cell will preferentially recombine inside through the cell instead of being extracted at the top and bottom contacts) in the cell, created by secondary phases of CIGS (e.g., Cu 2-x Se) or sodium compounds, which were indeed detected on the degraded surfaces. [22][23][24][25] Alkali elements (Na, K) are observed to be redistributed after aging.…”

“…This layer contains some alkali elements (Na, K) at grain boundaries, which improve its electronic ability (increase in charge carrier concentration, passivation of defect at grain boundaries 19 ) but can negatively influence stability against humidity 20 . Pure CIGS degradation is usually described in the literature by diffusion mechanisms of copper 21 or sodium 17,20,22 and oxidation 21,23 . The performance loss of the CIGS layer was described in the literature as occurring due to the formation of shunting paths (through which the electrons produced in the cell will preferentially recombine inside through the cell instead of being extracted at the top and bottom contacts) in the cell, created by secondary phases of CIGS (e.g., Cu 2‐x Se) or sodium compounds, which were indeed detected on the degraded surfaces 22–25 .…”