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

Abstract

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.

Effect of K Doping on the Performance of Aqueous Solution‐Processed Cu(In,Ga)Se2 Solar Cell

“…[ 25,26 ] In Figure 1b, the Raman peaks for P‐CIGS without K film are observed at around 293 and 339 cm −1 , identified to the A 1 mode and B 2 /E mode of Cu(In,Ga)S 2 , [ 27 ] while for its selenized film, these Raman peaks are almost invisible and new peaks around 177 and 218 cm −1 appear, which are identified to the A 1 mode and B 2 /E mode of Cu(In,Ga)Se 2 , respectively. [ 28 ] The same phenomenon occurred with the K‐doped precursor film and its selenized film. No peaks of the Cu 2−x Se secondary phase were detected.…”

Fundamental Understanding on Selenium Electrochemistry: From Electrolytic Cell to Advanced Energy Storage

“…d) Admittance spectroscopy and density of defect states of CIGS solar cells treated by KSCN, GaCl 3 , and GaCl 3 & KSCN. Reproduced with permission from Gao et al [86] Copyright 2021, American Chemical Society.…”

“…2024, 7, e12664 improved OCP of 0.65 V and a fill-factor of 72.21%. Gao et al [86] spun GaCl 3 solution onto CIGS surface for increasing the Ga content on the CIGS surface. As shown in Figure 11d, after CIGS was treated by potassium thiocyanate (KSCN), GaCl 3 and GaCl 3 & KSCN solutions, the activation energy changed to 57, 79, and 59 meV, respectively.…”

Dielectric Front Passivation for Cu(In,Ga)Se2 Solar Cells: Status and Prospect

“…[ 40 ] Absorber layers made with the sequential process have often no Ga gradient at the front and may be applied afterward by a postdeposition treatment. [ 41 ] The Ga gradient at the front reduces thermalization losses due to the wider gap and cause a beneficial conduction spike at the CdS/CIGSe interface. [ 42 ] A spike is beneficial for the V oc , but when the spike is too high, it will cause a blocking effect.…”