Optical monitoring and control of three-stage coevaporated Cu(In1−xGax)Se2 by real-time spectroscopic ellipsometry
Real-time spectroscopic ellipsometry (RTSE) has been applied for in situ monitoring and control of thin-film copper-indium-gallium-diselenide, i.e., Cu(In1−xGax)Se2 (CIGS), deposition by high vacuum coevaporation in the three-stage process used for efficient photovoltaic devices. Initial studies have been performed on a ∼0.7-µm CIGS layer deposited on crystal silicon to minimize surface roughness and to develop an accurate structural/ optical model of the Cu-poor-to-Cu-rich and Cu-rich-to-Cu-poor transitions that define the ends of the second (II) and third (III) stages of growth, respectively.With a better understanding of the surface achieved through this model, correlations can be made between the surface state and the unprocessed RTSE data {ψ(t), Δ(t)}. During deposition in the solar cell configuration with 2- µm-thick CIGS on a Mo-coated glass substrate, indications of the Cu poor-to-rich and Cu rich-to-poor transitions appear clearly in {ψ(t), Δ(t)}, enabling direct control of stage II and III transitions. The transition times deduced optically are in good agreement with those identified from the film/substrate emissivity by tracking the substrate heater power. It is clear, however, that RTSE can provide higher sensitivity to these transitions and is, therefore, suitable for improved control of three-stage CIGS deposition.
Study of Indium Chloride Vapor Treatment on Cu(In,Ga)Se2 Semiconductor Thin Films
The recrystallization by indium chloride of Cu(In,Ga)Se2 thin films deposited by co-evaporation at 350°C was studied. The process of recrystallization consists of the post-deposition treatment of CIGS sample by InCI3 vapor for 30 minutes with emphasis on grain growth. The treatment resulted in uniform increased grain size and improved crystallinity. XRD measurements suggests the formation of indium rich phase. Dynamic SIMS were also performed to further understand the process, phase separation and the extent of gallium depletion.
High efficiency thin-film Cu(In,Ga)Se/sub 2/-based photovoltaic devices: progress towards a universal approach to absorber fabrication
The formation chemistry of Cu(In,Ga)Se/sub 2/ by several reaction paths has been considered, and growth models of these processes have been developed. The results suggest a simple, reproducible approach to the formation of the multinary compound. The foundation of a universal process for the fabrication of Cu(In,Ga)Se/sub 2/-based solar cells is presented. Several embodiments of the process make it self-limiting with moderate compositional tolerances and simple endpoint detection. It is applicable to different device structures, and scalable to a variety of hybrid deposition technologies. A growth model is presented that correctly describes this process and related ones. Novel CuInSe/sub 2/ single-layer and Cu(In,Ga)Se/sub 2CuGaSe/sub 2/ multilayer absorber structures have been fabricated by physical vapor deposition using this process. Laboratory-scale photovoltaic devices demonstrate a total-area efficiency of 13.3%.<<ETX>>