Dominant Processing Factors in Two-Step Fabrication of Pure Sulfide CIGS Absorbers

Abstract

Pure sulfide CIGS solar cells are interesting candidates for standalone solar cells or top cells in a tandem configuration. To understand the limits and improve the power conversion efficiency of these devices, a comprehensive approach aimed at composition, interface, and process engineering should be employed. Here, the latter was explored. Using a two-step fabrication technique and one-variable-at-a-time methodology, we found the four processing factors affecting the absorber the most. While two were already backed by the previous literature, we found new and statistical evidence for two other important factors as well. The impact of alkali barrier diffusion was also established with statistical significance and under various processing conditions. Furthermore, the absorber roughness for samples without a barrier indicated a significant negative linear correlation with the devices’ efficiency. This contribution could aid engineers in more efficient process designs.

Benefits of Low Electron-Affinity Material as the N-Type Layer for Cu(In,Ga)S2 Solar Cell

“…The band gap of the CIGSe 2 material group can be adjusted between 1.0-1.7 eV, whereas the band gap of the CIGS 2 material group can be modified between 1.5-2.4 eV [5,6]. A variation of CIGSe 2 materials with the band gap in the narrower range is suitable for the bottom cell application [7], while the wider band gap CIGS 2 materials are suitable for the top cell application [8]. In addition to that, the band gap of low-Ga CIGS 2 is also very close to the ideal single-junction solar cell band gap for the best spectral matching application [9,10].…”

Formation of Cu(In,Ga)S2 chalcopyrite thin films following a 3-stage co-evaporation process

“…While a pure selenide absorber layer demonstrated 22.6 % record efficiency [2], devices based on pure sulfides remains lower with a 15.5 % record efficiency achieved using an absorber with a bandgap below 1.6 eV [3]. Nevertheless, by combining both improved material properties and growth process understanding, several groups have shown improved performance launching pure sulfide based devices towards much higher efficiency [4,5]. Moreover, the bandgap of CuIn 1-x Ga x S 2 can be tuned between 1.5 eV and 2.4 eV by increasing x from 0 through 1 [6].…”

Investigating the experimental space for two-step Cu(In,Ga)(S,Se)2 absorber layer fabrication: A design of experiment approach

“…In this method of making these types of chalcogenide absorber layers, essentially a metal precursor of copper-gallium and indium is selenized (and/or sulfurized) with a solid or gaseous source. Next to valuable insights from the work of Intermolecular [6], some clarity on processing of pure selenide and pure sulfide variations of these chalcogenides has been recently offered by Solliane and imec, respectively [7,8]. On the other hand, as Kato et al suggested [9], every tool and fabrication design might need its own process optimization for best results.…”