A Novel Ge-Doping Approach for Grain Growth and Recombination Suppression in Buffer-Free CIGSe Solar Cells

Area of Science:

• Materials Science
• Photovoltaics
• Semiconductor Physics

Background:

• Copper Indium Gallium Selenide (CIGSe) is a key material for thin-film solar cells.
• Improving CIGSe crystallinity and reducing defects are crucial for enhancing solar cell efficiency.
• Buffer-free solar cell architectures offer potential for simplified manufacturing.

Purpose of the Study:

• To investigate the effects of Germanium (Ge) doping on CIGSe absorber properties.
• To analyze the impact of Ge doping on the performance of CIGSe buffer-free solar cells.
• To understand the relationship between Ge doping, crystallinity, defects, and device performance.

Main Methods:

• Fabrication of Ge-doped CIGSe absorbers using a two-step process: sputtering and selenization annealing.
• Characterization of absorber crystallinity and defects using advanced analytical techniques.
• Performance evaluation of resulting CIGSe buffer-free solar cells.

Main Results:

• Ge doping significantly promoted grain growth in CIGSe absorbers.
• Ge was undetectable in the final absorbers due to volatilization during annealing.
• Ge doping improved CIGSe crystallinity without introducing new impurity phases or Ge-related defects.
• Ge doping induced Se loss, leading to Se vacancy defects that can negatively impact performance.
• Ge doping increased the contact potential difference at grain boundaries, reducing carrier recombination.
• Overall device performance was improved due to enhanced crystallinity and optimized grain boundary properties.

Conclusions:

• Ge doping is an effective strategy to enhance CIGSe crystallinity for buffer-free solar cells.
• While Ge itself is lost, its doping influences grain growth and electrical properties favorably.
• Optimized grain boundaries and suppressed recombination contribute to improved solar cell efficiency.