Molybdenum cathodic sputtering target

Overview
CIGS (copper‑indium‑gallium‑selenide) thin‑film solar cells reach high laboratory efficiencies. Sodium in the absorber improves device performance even at low concentrations. MoNa (molybdenum‑sodium) sputtering targets provide a controlled sodium source during back‑contact deposition to adjust sodium dosing in the absorber and improve module reproducibility.

Sodium introduction and layer concept
In standard CIGS production sodium often originates from soda‑lime glass substrates and diffuses into the absorber at typical processing temperatures (~500 °C). Glass‑derived sodium is variable depending on glass type and storage. Depositing a dedicated MoNa layer as a controlled Na source gives reproducible sodium supply: a diffusion barrier (e.g. SiNx on glass or Cr/W‑based barrier on steel foil) is applied to the substrate, a thin MoNa layer is sputtered, then a pure molybdenum layer is deposited as the back electrode. MoNa layer thickness and sputter conditions control the sodium dosage. Conventional PVD/magnetron sputtering equipment (DC capable) is used to deposit the layers.

Key product properties and manufacturing

• Powder‑metallurgical production yields a fine, homogeneous distribution of sodium compounds between molybdenum grains.
• High metallic purity (> 99.7%) to limit detrimental impurities (e.g. Fe, Cr) that reduce cell performance.
• Available Na doping options (typical nominal values offered): 5% and 10% Na in the target (manufacturer reports corresponding approx. 1.3 wt.% and 2.6 wt.% in the absorber context).
• Electrical conductivity suitable for DC sputtering (typical range: 5–10 MS/m).
• Produced as planar targets and as rotary targets (rotary targets can offer higher material yield in production).

Advantages (at a glance)

• Metallic purity > 99.7%
• Homogeneous microstructure and chemical composition
• Adjustable Na doping via target composition and layer thickness
• Electrical conductivity compatible with DC magnetron sputtering (approx. 5–10 MS/m)

Research and application notes
MoNa sputtering targets have been investigated by research groups for controlled sodium incorporation in CIGS absorbers. Studies indicate that MoNa back contacts enable reproducible Na doping and can increase device efficiency; examples include work on both rigid (glass) and flexible (steel foil) substrates. Optimization of sputter parameters and MoNa layer design is important to maximize Na incorporation while avoiding contamination.

Technical characteristics / specifications

• Material: molybdenum doped with sodium (MoNa)
• Metallic purity: > 99.7%
• Na content (examples offered): 5% and 10% (manufacturer‑reported equivalents in absorber context: ≈ 1.3 wt.% and 2.6 wt.% )
• Electrical conductivity: approx. 5–10 MS/m
• Forms: planar targets and rotary (rotable) targets
• Manufacturing: powder metallurgy for fine, even Na distribution
• Deposition: conventional PVD/magnetron sputtering (DC capable); Na dosage controlled via MoNa layer thickness and sputter parameters
• Typical processing note: Na diffusion from substrates aided at ~500 °C; use in combination with diffusion barrier layers on substrate