Strength, stiffness, and microstructure of Cu(In,Ga)Se2 thin films deposited via sputtering and co-evaporation

Abstract

This work examines Cu(In,Ga)Se2 thin films fabricated by (1) selenization of pre-sputtered Cu-In-Ga and (2) co-evaporation of each constituent. The efficiency disparity between films deposited via these two methods is linked to differences in morphology and microstructure. Atomic force microscopy and scanning electron microscopy show that selenized films have rougher surfaces and poor adhesion to molybdenum back contact. Transmission electron microscopy and electron energy loss spectroscopy revealed multiple voids near the Mo layer in selenized films and a depletion of Na and Se around the voids. Residual stresses in co-evaporated films were found to be ∼1.23 GPa using wafer curvature measurements. Uniaxial compression experiments on 500 nm-diameter nanopillars carved out from co-evaporated films revealed the elastic modulus of 70.4 ± 6.5 GPa. Hertzian contact model applied to nanoindentation data on selenized films revealed the indentation modulus of 68.9 ± 12.4 GPa, which is in agreement with previous reports. This equivalence of the elastic moduli suggests that microstructural differences manifest themselves after the yield point. Typical plastic behavior with two distinct failure modes is observed in the extracted stress-strain results, with the yield strength of 640.9 ± 13.7 MPa for pillars that failed by shearing and 1100.8 ± 77.8 MPa for pillars that failed by shattering.

Silver Surface Treatment of Cu(In,Ga)Se2 (CIGS) Thin Film: A New Passivation Process for the CdS/CIGS Heterojunction Interface

“…According to the results of Luo et al, larger grains can result in better approximate spherical contact. [ 41 ] As a result, the excess Ag (ACGI > 1) doped into CIGS films will produce nearly spherical‐shaped grains, which is consistent with the results obtained from Figure 1d,e.…”

Optimization of Intrinsic ZnO Thickness in Cu(In,Ga)Se2-Based Thin Film Solar Cells

“…Even though diverse fabrication processes of CIGS light absorbers have been successful with efficiencies close to 20%, the most successful processes with greater than 20% electrical conversion efficiency are three-stage co-evaporation (22.6% by Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)) [8] and two-step metallization-selenization processes (23.35% by Solar Frontier) [3]. The microstructural characteristics of the CIGS absorber, including the density, grain boundaries, grain size, and surface smoothness/roughness, are dependent on the fabrication processes [9]. For example, the CIGS absorber prepared by a three-stage co-evaporation process exhibited a smooth and dense surface morphology, while the CIGS obtained from a two-step metallization-selenization process exhibited high surface roughness [10].…”

Microstructure, Mechanical and Corrosion Behaviors of CoCrFeNiAl0.3 High Entropy Alloy (HEA) Films

“…This would be costly, impeding its practicability for real-life applications [2,9,14,15]. Alternatively, it is widely known that thin films can be used as a protective and mechanically enhancing surface coating on the substrate [16][17][18][19][20]. Therefore, incorporating HEA as a thin film material would tremendously extend the scope of its practical application.…”