Substitution of the CdS buffer layer in CIGS thin‐film solar cells

This contribution provides an overview of current activities in the area of alternative buffer layers for Cu(In,Ga)(S,Se)2 (CIGS) thin‐film solar cells. Good cell and module results were achieved by replacing the standard Cds buffer with Zn(O,S), In2S3, (Zn,Sn)Oy or (Zn,Mg)O grown by various methods like chemical bath deposition (CBD), thermal evaporation, sputtering, atomic layer deposition, and spray ion layer gas reaction. The “dry” deposition methods like sputtering and thermal evaporation could be favorable in an industrial environment on glass substrates or application in a roll‐to‐roll coater. Significant progress was made within the last two years for various Cd‐free CIGS devices. We list current records for cells with alternative buffers, e. g. Zn(O,S)‐buffered champion cells with efficiencies between 18—20 % and In2S3‐buffered cells with 16—17 %. Both materials have the potential to substitute CdS with efficiencies approaching the 20 % mark already surpassed by CIGS cells with CBD CdS buffers.