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We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) thin films using thermal evaporation from copper, zinc and tin pellets and post-annealing in a sulfur atmosphere. The effects of chemical composition were studied both on the absorber layer properties and on the final solar cell performance. It is confirmed that CZTS thin film chemical composition affects the carrier concentration profile, which then influences the solar cell properties. Solar cells using a CZTS thin film with composition ratio Cu/(Zn+Sn) = 0.87, and Zn/Sn = 1.24 exhibited an open-circuit voltage of 483 mV, a short-circuit current of 14.54 mA/cm2, a fill factor of 37.66 % and a conversion efficiency of 2.64 %. Only a small deviation from the optimal chemical composition can drop device performance to a lower level, which confirms that the CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region.

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 1.6 eV to 1.7 eV can be achieved by increasing the Ga content, these solar cells show a maximum efficiency at -1.3 eV 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.

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