Steps toward industrialization of Cu-III-VI2 thin-film solar cells: a novel full in-line concept

In order to manufacture Cu-III-VI2 thin-film solar cells in much larger area and full speed as compared to the conventional evaporation method with the CdS layer deposited by CBD, a novel full in-line fabrication concept was developed, which includes in-line cleaning of substrates, sequential in-line sputtering/RTP steps for the fabrication of absorber, buffer layer and window-layer. A novel method named ‘MO sputter’ was developed in which the metal–organic (MO) TMGa used as a reactant gas, was introduced into the sputter for very fine-tuning the sputter-deposited metal precursor layers compositions, which could fulfill the requirement of Cu(InxGa1−x)(S,Se)2 with the gradient bandgap, which help to obtain the precisely controlled, designated electrical characteristics for the device making. Then rapid thermal process (RTP) was utilized for sulfurization or selenization of the metal precursor layers. It has been found that Ga/(Ga+In) ratio incorporated in the films was increased linearly from 0.47 to 0.60 with increasing the TMGa gas flow rate at 450 °C substrate temperature. Single phase Cu(InxGa1−x)S2 films have been obtained by optimizing the deposition parameters. Using the in-line sputtering/RTP sulfurization techniques, the ZnS buffer layer can also be prepared which can ensure not to use the hazardous CdS layer, and together with the sputter-deposited ZnO electrode, this could promote genuine realization of the large-scale production and lay down foundation for the full in-line manufacture of the ultra-high efficiency Cu-III-VI2 thin film solar cells.