Cu(In, Al)S2 thin films prepared from rapid thermal annealing of Cu-In-Al-S precursors and Cu-In-Al alloys

Cu(In,Al)S₂ (CIAS) absorbers had heavy roughness and a lot of particles like islands, in addition, the grain-size was small in the co-evaporation at high substrate temperature of 500°C~, resulted in the low efficiency. To enhance the flatness and the crystal growth (large grain-size), we investigated CIAS absorbers prepared from post-annealed Cu-In-Al-S precursors and sulfurized Cu-In-Al alloys. A rapid thermal processing was used in the post-annealing and the sulfurization. The flatness of the post-annealed Cu-In-Al-S precursors enhanced but the efficiency of solar cells used the precursors was low due to the incomplete crystal growth. In contract, the sulfurized Cu-In-Al alloys became the separated layers which were the large grain-size layer and the small grain-size layer. It was revealed that the large grain-size layer and small one were CuInS₂ and CIAS from both an XRD and an EDS analysis of the detached film. Furthermore, 9.6% efficiency was obtained in the solar cell used the sulfurized Cu-In-Al alloy.