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

Abstract

Molecular beam epitaxy was used to fabricate Ag(In,Ga)Se 2 (AIGS) thin films. To improve the diffusion of Ag, hightemperature 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 8C led to decomposition of the AIGS film, desorption of In, and deterioration of its crystallinity. The most appropriate deposition temperature was 590 8C 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 8C. When the annealing temperature was further increased to 610 8C, the performance of the cell deteriorated due to loss of the out-ofplane Ga gradient.

Efficiency Boost of (Ag0.5,Cu0.5)(In1‐x,Gax)Se2 Thin Film Solar Cells by Using a Sequential Process: Effects of Ag‐Front Grading and Surface Phase Engineering

“…[30] The selected selenization temperature for ACIGSe (510 °C) is substantially lower than that of CIGSe (590 °C) because the phase decomposition (Ag 2 Se) occurs at a high selenization temperature for ACIGSe. [31] Although the selenization temperature is reduced for ACIGSe, Ag-alloying can still induce grain growth at a low selenization temperature possibly due to the presence of a liquid AgInSe 2 phase for T-ACIGSe during selenization. [13] The cross sectional view of the scanning electron microscopy (SEM) images clearly identifies the enhanced grain growth for T-ACIGSe (Figure S3, Supporting Information).…”

Novel Ag-based thin film solar cells: concept, materials, and challenges

“…Finally, the corresponding devices obtained had 9.4% PCE. Simultaneously, Nakada et al 67 used high deposition and annealing temperatures to prepare AIGS thin films. It is shown that at higher deposition and annealing temperatures, the diffusion rate of Ag is higher, and its distribution is more uniform.…”

Advance Supply of Ag and Ga–Se for Increased Backside Ga and Enhanced Cu(In,Ga)Se2 Solar Cell Efficiency

“…Most studies investigating the role of Ag insertion in the absorber layer have focused on standard GGI profiles without a detailed explanation of the effects of high Ga concentrations in (Ga,Cu)­(In,Ga)­Se 2 (ACIGS) solar cells. For example, the substitution of Ag or Cu and the resulting slight bandgap widening can be attributed to anion displacement/bond length effects, changes in the s–s orbital repulsion in the conduction band minimum, or changes in the p–d orbital repulsion in the valence band maximum. , The presence of liquid channels comprising Ag–Se along the grain boundaries (GBs) enhances Ga interdiffusion, improves the grain size, and facilitates the recrystallization of CIGS at relatively low temperatures. − Additionally, the incorporation of Ag mitigates the degree of structural disorder within the CIGS lattice by lowering the melting point of (Ag,Cu)­(In,Ga)­Se 2 (ACIGS) chalcopyrites. , Similar improvements have been observed for Ag-alloy CIGS. − In this context, the current study leveraged the tunable bandgap property of CIGS to precisely tailor the shape of the double Ga grading profile in both the notch and back regions of CIGS and ACIGS solar cells. This study’s findings reveal the beneficial impact of a sizable columnar grain structure with high Ga content near the back surface contact, facilitating Ga diffusion and reinforcing defect annihilation.…”