The spray-ILGAR® (ion layer gas reaction) method for the deposition of thin semiconductor layers: Process and applications for thin film solar cells

The spray Ion Layer Gas Reaction (ILGAR) process starts with ultrasonic nebulisation of the precursor solution, e.g. InCl3/ethanol for our successful buffer material In2S3. In an aerosol assisted chemical vapour deposition (AACVD) type reaction an In(O,OH,Cl) film is deposited on a heated substrate and is subsequently converted to In2S3 by H2S gas. The cycle of these steps is repeated until the required layer thickness is obtained. The robust and reproducible process allows a wide control of composition and morphology.Results of this “spray-ILGAR” method with respect to process, material properties and its application depositing the buffer layer in chalcopyrite solar cells are reviewed. New aspects such as the investigation of the complex chemical mechanism by mass spectrometry, the process acceleration by the addition of H2S gas to the aerosol, the controlled deposition of ZnS nano-dot films and finally the latest achievements in process up-scaling are also included.Solar cells based on industrial Cu(In,Ga)(S,Se)2 absorbers (Avancis GmbH) with a Spray-ILGAR In2S3 buffer reached 14.7% efficiency (certified) and 15.3% with a ZnS/In2S3 bi-layer buffer comparable to reference cells using standard CdS buffer layers deposited by chemical bath deposition (CBD).The quasi-dry, vacuum-free ILGAR method for In2S3 buffer layers is well suited for industrial in-line production and is capable of not only replacing the standard buffer material (the toxic CdS) but also the often slow CBD process. A tape coater for 10 cm wide steel tape was constructed. It was shown that In2S3 layers could be produced with an indium yield better than 30% and a linear production speed of 1m/min. A roll-to-roll pilot production line for electrochemically deposited Cu(In,Ga)Se2 with ILGAR buffer is running in industry (CIS-Solartechnik, Hamburg). A 30x30 cm2 prototype of an ILGAR in-line coater developed by Singulus and Helmholtz Zentrum Berlin is currently being optimised. First 30×30 cm2 encapsulated modules achieved efficiencies up to 13.0% (CdS buffered reference 13.3%).

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