Interface Engineering for High-Efficiency Solution-Processed Cu(In,Ga)(S,Se)₂ Solar Cells via a Novel Indium-Doped CdS Strategy

Indium doping of cadmium sulfide (CdS) by chemical bath deposition (CBD) can be an efficient strategy to boost the CIGSSe efficiency. However, limited by the extremely low solubility of In2S3, it is difficult to increase the In doping contents and inhibit the band energy-level regulation for CdS through the traditional CBD process. In this work, we perform a novel CBD method to prepare an indium-doped CdS (In:CdS) buffer, in which the indium source is sequentially slowly added in the growing aqueous solution. In this process, the In ion concentration involved in the real-time deposition is significantly reduced. Thus, compact and uniform In:CdS with higher indium doping content is obtained. Indium doping can elevate the CdS conduction band edge and construct a more favorable spike band alignment with a CIGSSe absorber. Moreover, it introduces efficient carrier transport and reduced interface defect density. As a result, improved CIGSSe heterojunction quality is realized by utilizing In:CdS. Also, the solution-processed CIGSSe device with In:CdS as a buffer yields a high efficiency of 16.4%, with a high VOC of 670 mV and an FF of 75.3%.