Tuning Conductivity of Lead-Free Cs₂AgBiBr₆ Double Perovskite Ternary Composite with PEDOT:PSS and Carbon Black for Supercapacitor Application

Abstract

Lead-based halide perovskites have been widely used as efficient energy materials due to their superior optoelectronic properties and mixed electronic–ionic conductivity. However, lead toxicity has been one of the key challenges for commercialization. Recently Cs2AgBiBr6, a lead-free double perovskite, has garnered significant interest due to its exceptional stability, nontoxic nature, and promising optoelectronic properties. But because of the low electronic and ionic conductivity of bismuth-based double perovskites, there is a challenge for their use in energy storage applications. To resolve this issue, we have incorporated carbon black and a conducting polymer poly(2,3-dihydrothieno-1,4-dioxin)-poly (styrene sulfonate) (PEDOT:PSS) as electronic and ionic conductivity agents respectively into the Cs2AgBiBr6 porous electrode. This ternary composite exhibits over 40% enhancement in specific capacitance as well as specific energy density compared with a binary composite of carbon black with a perovskite electrode. There is no significant change in the power density. However, only PEDOT:PSS as charge transporting materials in perovskite matrix results in lower energy density and power density despite lower charge transfer resistance (Rct) at the electrode/electrolyte interface and higher dc ionic conductivity compared to perovskite/carbon composite electrodes. From the electrochemical impedance spectroscopy analysis, it is evident that balanced ionic and electronic conductivities are necessary to achieve optimal performance in lead-free perovskite-based supercapacitors. We also fabricated a solid-state symmetric supercapacitor using a quasi-solid-state gel electrolyte.