Effect of chemical treatments on nm-scale electrical characteristics of polycrystalline thin film Cu(In,Ga)Se2 surfaces

• We compare the electrical activity of the grain boundaries of CIGS films with sulfide, selenide and oxide surface terminations.
• We find differences in grain boundary electrical activity to stem directly from the differences in O, S, and Se electronegativities;
• Both oxidation and sulfurization can passivate the grain boundaries of the CIGS films;
• Oxidation increases n-type band bending, which impedes photogenerated electron transport;
• (Subsequent) Sulfurization increases p-type band bending at grain boundaries, which helps this transport.

Conducting Probe AFM. CP-AFM, was used to follow how chemical etching, oxidation, and sulfurization affect the surface nanoscale electrical characteristics of polycrystalline Cu(In,Ga)Se2 (CIGS) thin films. Band bending at grain boundaries (GBs) on the surface was studied and analyzed by CP-AFM – measured photocurrents. We find that both oxidation and sulfurization can passivate the GBs of the CIGS films; oxidation increases n-type band bending, which impedes the transport of photogenerated electrons, while sulfurization increases p-type band bending at GBs, which helps this transport. Differences in effects between surface terminations by sulfide, selenide and oxide were analyzed. The effects of these treatments on the electrical activity of the GBs of the films, as well as the importance of the use of chemical bath deposition of the CdS buffer, are explained within a defect surface chemistry model.

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