Cadmium Sulfide Quantum Dots–Organometallic Halide Perovskite Bilayer Electrode Structures for Supercapacitor Applications

Supercapacitors are attracting great attention because of their fast charging–discharging ability as well as their high power density. The current research in this area focuses mainly on exploring novel low-cost electrode materials with higher energy and power densities. In this work, thin-film electrochemical capacitors were fabricated using layers of self-synthesized cadmium sulfide quantum dots and organometallic halide perovskite materials as active electrodes. Organometallic halide perovskites exhibit interesting ionic responses as well as extraordinary electronic properties. These properties are exploited in fabricating the electrochemical capacitors, and the devices showed excellent cycling ability with stable capacitance outputs beyond 4000 cycles. Impedance spectroscopy measurements revealed that perovskites do not only serve as active electrodes but also as solid electrolytes, thereby enhancing the capacitance of the devices and hence the energy densities. The layers provide high surface areas for electrolytes to access the electrode materials; reasonably low charge transfer resistance and small relaxation time were also observed. This work opens new opportunities for developing thin-film supercapacitors using low-cost electrode materials and employing a facile, inexpensive solution-process coating.