Controllable Growth of Ga Film Electrodeposited from Aqueous Solution and Cu(In,Ga)Se2 Solar Cells

New Solution-Processed Surface Treatment to Improve the Photovoltaic Properties of Electrodeposited Cu(In,Ga)Se2 (CIGSe) Solar Cells

The surface Ga content for a CIGSe absorber was closely related to variation in the open-circuit voltage (V_OC), while it was generally low on a CIGSe surface fabricated by two-step selenization. In this work, a solution-processed surface treatment based on spin-coating GaCl₃ solution onto a CIGSe surface was applied to increase the Ga content on the surface. XPS, XRD, Raman spectroscopy, and band gap extraction based on the external quantum efficiency response demonstrated that GaCl₃ post deposition treatment (GaCl₃-PDT) can be used to enhance the Ga content on the surface of a CIGSe absorber. Meanwhile, a solution-processed surface treatment with KSCN (KSCN-PDT) was employed to form a transmission barrier for holes by moving the valence band maximum downward and decreasing the interface recombination between the CdS and CIGSe layers. Admittance spectroscopy results revealed that deep defects were passivated by GaCl₃-PDT or KSCN-PDT. By applying the combination of GaCl₃-PDT and KSCN-PDT, a champion device was realized that exhibited an efficiency of 13.5% with an improved V_OC of 610 mV. Comparing the efficiency of the untreated CIGSe solar cells (11.7%), the CIGSe device efficiency with GaCl₃-PDT and KSCN-PDT exhibited 15% enhancement.

A Novel Metal Precursor Structure for Electrodepositing Ultrathin CIGSe Thin-Film Solar Cell with High Efficiency

The two-step process of electrodeposition and selenization is one of the most effective methods for producing CIGSe and CZTSe solar cells at a low cost. However, it is difficult to prepare the ultrathin CIGSe absorber by electrodeposition due to the nonuniform deposition of Cu on the Mo substrate. In this study, Cu was deposited on a Sb film instead of a Mo film, and the 3D growth mode of Cu was changed. Uniform and smooth ultrathin Cu films were fabricated on the Sb film using a pulse frequency over a range from 1000 to 10,000 Hz and a pulse current density ranging from 31.25 to 62.5 mA/cm². Owing to the improved uniformity of Cu/In/Ga films, the thickness of the CIGSe absorber was reduced from 2 to 0.36 μm with Sb incorporation. In addition, the effects of Sb-doping on the CIGSe absorbers and the device performance were investigated. The crystallinity of the CIGSe films was improved, and the interface recombination of the solar cells was reduced by Sb incorporation. Ultimately, CIGSe thin-film solar cells with efficiencies of 5.25 and 11.27% were obtained with CIGSe absorber thicknesses of 0.36 and 1.2 μm, respectively.