Near‐Surface [Ga]/([In]+[Ga]) Composition in Cu(In,Ga)Se₂ Thin‐Film Solar Cell Absorbers: An Overlooked Material Feature

Abstract

The chemical and electronic structures in the near‐surface region of Cu(In,Ga)Se2 thin‐film solar cell absorbers are investigated using nondestructive soft and hard X‐ray photoelectron spectroscopy. In addition to a pronounced surface Cu‐depletion, the [Ga]/([In]+[Ga]) composition indicates that the topmost surface is Ga‐poor (or In‐rich). For the studied depth region, common depth profiling techniques generally fail to provide reliable information and, thus, the near‐surface chemical and electronic structure profiles are often overlooked. The relation between the observed near‐surface elemental compositions and the derived electronic properties of the absorber material is discussed. It is found that the surface band gap energy crucially depends on the Cu‐deficiency of the absorber surface and suggests that it is, in this region, only secondarily determined by the [Ga]/([In]+[Ga]) ratio.

NaF/RbF-Treated Cu(In,Ga)Se2 Thin-Film Solar Cell Absorbers: Distinct Surface Modifications Caused by Two Different Types of Rubidium Chemistry

“…The GGI calculated from electrons with a smaller IMFP is higher than the one calculated from electrons with larger IMFP, and so, we conclude that all samples have a Ga-enriched surface region. This enrichment is in contrast to previous studies on LT and HT absorbers, exhibiting Ga-deficient surfaces. The Ga concentration at the surface might have an impact on the effects induced by the alkali PDT since it was recently proposed that RbF PDT only results in the formation of Rb-In-Se-type surface species when performed on In-containing chalcopyrites .…”

Measurement of shunt resistance and conduction band offset in Cu(In, Ga)Se2 solar cells through joint analysis of temperature and intensity dependence of open-circuit voltage and photoluminescence

“…31) Offsets may also be complicated by the presence of Cu depletion near the interface. 32) Despite a cliff-like offset, the fits are nonetheless dominated by absorber recombination, c , a as reported for materials in this Ga composition range. 5,33,34) Throughout the composition range, we find that c a increases dramatically with x.…”

New Solution-Processed Surface Treatment to Improve the Photovoltaic Properties of Electrodeposited Cu(In,Ga)Se2 (CIGSe) Solar Cells

“…The three-step (H 2 Se/Ar/H 2 Se) reaction process achieved a homogenized Ga distribution through a reduced Se supply. − However, the three-step process resulted in Ga depletion at the CIGSe surface due to the presence of InSe during the second annealing step, which significantly deteriorated the device performance. Félix et al reported a Ga-poor (or In-rich) topmost surface by investigating the near-surface Ga/(In + Ga) composition in CIGSe absorbers. The Ga-poor (or In-rich) topmost surface led to a reduction in the surface band gap, which deteriorated the open-circuit voltage.…”