Delafossite materials (Cu^IM^IIIO₂) are p-type metal oxides which can be used as hole transport layers in a wide range of heterojunction solar cells. These materials are interesting because of their crystal structure that can facilitate hole diffusion through the valance band. Maximizing the interfacial capacitance within porous nanocrystalline films of CuGaO₂ is a primary goal for enhancing their performance in solar cells. The electrochemistry of CuGaO₂ can reveal much information about the capacitance of the material and therefore the electronic density of valance band states. Here we have investigated the structural and electrochemical properties of CuGaO₂ nanocrystalline thin films in acetonitrile solution with LiClO₄ electrolyte. Nanocrystalline films are produced by dispersion of CuGaO₂ nanocrystals in a polymer solution designed to control the porosity of the resulting film.¹ We have used two different chain lengths of ethyl cellulose polymers (10 cps and 22 cps) to understand their impact on film morphology. As the film capacitance is related to surface area, a more porous film is expected to increase the film capacitance. In addition, we have also varied the CuGaO₂ : polymer ratio to find the optimum condition for enhanced film capacitance. Keeping CuGaO₂ : polymer ratio constant (1:1) we have changed percent weight of CuGaO₂ (15%, 12%, 10%, 8%, 6%) to find the best quality film by spin coating. The films were characterized by powder XRD where peak ratios for (003)/(006) and (012)/(006) planes were calculated to understand the orientation of nanocrystals within the film. Electrochemical impedance spectroscopy (EIS) was used to probe the electrochemical behavior and capacitance of the films. We are particularly observing the C_real values at low frequency for comparative study of various films. These studies find that C_real is maximized for 1:1 ratio of CuGaO₂ : polymer mixture. Among two different chain lengths of polymer, the films prepared from longer chain polymer shows higher C_real values.

Reference

1. Yeasmin, H., Bredar, A. R. C. & Farnum, B. H. Effect of Different Polyethylene Glycol (PEG) and Ethyl Cellulose on Impedance Spectroscopy of CuGaO ₂ Film. ECS Meet. Abstr. MA2021-01, 1027–1027 (2021).