High-temperature fabrication of Ag(In,Ga)Se₂ thin films for applications in solar cells

Molecular beam epitaxy was used to fabricate Ag(In,Ga)Se₂ (AIGS) thin films. To improve the diffusion of Ag, high-temperature deposition and high-temperature annealing methods were applied to fabricate AIGS films. The as-grown AIGS thin films were then used to make AIGS solar cells. We found that grain size and crystallinity of AIGS films were considerably improved by increasing the deposition and annealing temperature. For high-temperature deposition, temperatures over 600 °C led to decomposition of the AIGS film, desorption of In, and deterioration of its crystallinity. The most appropriate deposition temperature was 590 °C and a solar cell with a power conversion efficiency of 4.1% was obtained. High-temperature annealing of the AIGS thin films showed improved crystallinity as annealing temperature was increased and film decomposition and In desorption were prevented. A solar cell based on this film showed the highest conversion efficiency of 6.4% when annealed at 600 °C. When the annealing temperature was further increased to 610 °C, the performance of the cell deteriorated due to loss of the out-of-plane Ga gradient.