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 (VOC), 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 VOC 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.