Atom probe study of Cu-poor to Cu-rich transition during Cu(In,Ga)Se2 growth

Abstract

Atomic scale chemistry of polycrystalline Cu(In,Ga)Se2 (CIGSe) thin film has been characterized at key points of the 3-stage process using atom probe tomography. 3D atom distributions have been reconstructed when the layer is Cu-poor ([Cu]/([Ga] + [In]) < 1), Cu-rich ([Cu]/([Ga] + [In]) > 1), and at the end of the process. Particular attention has been devoted to grain boundary composition and Na atomic distribution within the CIGSe layer. Significant variation of composition is highlighted during the growing process, providing fundamental information helping the understanding of high efficiency CIGSe formation.

Na distribution in Cu(In,Ga)Se2 thin films: Investigation by atom probe tomography

“…Up until very recently, the lack of available analysis techniques combining both accurate spatial resolution and high elemental detection limits was restraining such investigations. Since 2010 and the first atom probe tomography (APT) analysis on CIGSe layers reported by Cadel et al[12], many information concerning grain boundaries (GBs) [13][14][15][16] and interface [17,18] compositions has been revealed by APT which confirms the relevance of this technique for the nanoscale characterization of polycrystalline CIGSe thin films.In this work, the chemistry of co-evaporated CIGSe layers has been investigated by APT and 3D atom distributions reconstructed with the aim of solving interrogations about Na distribution; a particular attention is paid on the composition of the absorbers at the vicinity of Na segregations.The investigated CIGSe layers were co-evaporated on Mo-coated soda-lime glass (SLG) substrates following the so-called "3-stage process". The nominal composition of the films, determined by Scanning Electron Microscope Electron Dispersive Spectroscopy (SEM-EDS), results in [Cu]/([In] + [Ga]) ratio (i.e., CGI) around 0.85 and [Ga]/ ([In] + [Ga]) (i.e., GGI) of 0.22.…”

“…Up until very recently, the lack of available analysis techniques combining both accurate spatial resolution and high elemental detection limits was restraining such investigations. Since 2010 and the first atom probe tomography (APT) analysis on CIGSe layers reported by Cadel et al [12], many information concerning grain boundaries (GBs) [13][14][15][16] and interface [17,18] compositions has been revealed by APT which confirms the relevance of this technique for the nanoscale characterization of polycrystalline CIGSe thin films.…”

“…[12], many information concerning grain boundaries (GBs) [13][14][15][16] and interface [17,18] compositions has been revealed by APT which confirms the relevance of this technique for the nanoscale characterization of polycrystalline CIGSe thin films.…”

Incorporation of alkali metals in chalcogenide solar cells

“…There are other disputed topics regarding the influence of Na in CIGSe: the promotion of MoSe 2 by Na [38,[49][50][51][52]; the exact location and effect of Na in the grain boundaries or in the bulk [43,53]; and the relation between oxidized compounds with sodium [5,[54][55][56][57]. The reason for these numerous contradictory results is likely connected with the different growth processes used for the deposition of CIGSe.…”

Characterization of group I-rich growth during (Ag,Cu)(In,Ga)Se<inf>2</inf> three-stage co-evaporation

“…Analogous to the Cu 2 Se-Ga 2 Se 3 pseudo-binary phase diagram [5], once ACIGS films pass stoichiometry, a Ag-Cu-Se compound is expected to be generated and the films will grow with excess group-I composition. This group-I rich growth in CIGS three-stage deposition has been suspected to have impact on grain size [6] and defects [7]- [9].…”