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Technologies for producing the components

Important for the economic production of thin-film solar cells are a high throughput combined with excellent, high-quality production yields. In order to achieve this, the industry is pursuing two main technological directions:

(1) Sequential processes with H2 Se or a quick, reactive implementation of Se and metal layers (RTP)

Polycrystalline CuInS2 or Cu(In,Ga)Se2 thin films are deposited on a substrate (e.g. Mo-coated glass) consisting of metallic Cu-In precursor layers in the presence of H2 Se, H2 S or elementary selenium and sulphur vapour (chalcogen gas, process gas) with temperatures of around 500 °C to 600 °C.

If the implementation occurs within a few seconds, this is known as rapid thermal processing (RTP). The necessary high heating rates with temperature gradients of up to 500 °C per minute are achieved using strong radiant heaters, for example halogen or quartz lamps. This technology has successfully made the transition from the laboratory to industrial production. It has considerable potential for reducing costs, enables a high throughput and can be scaled up to large production rates.

(2) CIGSe multi-stage co-evaporation process

Alternatively, Cu(In,Ga)Se2 (CIGSe) layers can also be produced using coevaporation by vaporising Cu, In, Ga and Se more or less simultaneously on a heated substrate in a vacuum. Figure 22 shows the rate profile for these elements in the multi-stage process. In addition to selenium, only In and Ga are initially deposited in order to generate an In-Ga-Se precursor layer on the approximately 330 °C glass substrate coated with Mo. In the second stage, Cu and Se are applied to convert this to Cu(In,Ga)Se2 at a substrate temperature of more than 500 °C. This complex manufacturing process is monitored and controlled with the in-situ laser light scattering (LLS) process control system developed at the Helmholtz Zentrum Berlin forMaterials and Energy.

Therefore, Cu is already evaporated during the first stage of a two-stage process or, in inline processes, the suitable characteristic for the deposition rates is established by translating the substrate using static evaporation sources.

Using multistage co-evaporation, efficiencies of up to 20.3% have already been achieved in the laboratory; industrially generated, commercially available CIGSe modules have efficiencies of up to 13%.

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