Challenges in deposition of wide band gap copper indium aluminum gallium selenide (CIAGS) thin films for tandem solar cells

Copper indium gallium diselenide (CIGS) based solar cells have shown efficiencies > 20% on the lab scale and are already in commercial production. Even though the optimal band gap of 1.6eV to 1.7eV can be achieved by increasing the Ga content, these solar cells show a maximum efficiency at ~1.3eV and any further increase in the Ga concentration and band gap results in lower efficiencies due to bulk and interfacial traps. This also prevents the use of wide band gap CIGS layer as a top cell for harvesting the solar cell spectrum in a tandem cell configuration. This paper reports the manufacturing challenges on the production of wide band gap aluminum doped CIGS layers (CIAGS) and devices fabricated using this material. We have fabricated 11.3% efficient solar cells using the CIAGS absorber layers.