High-voltage solar energy conversion based on ZIF-67-derived binary redox-quasi-solid-state electrolyte

Zeolitic imidazolate framework-67 (ZIF-67) nanoparticles were incorporated into a traditional redox quasi-solid-state nanogel polymer electrolyte system to form a color-tunable and energy-efficient binary redox-quasi-solid-state electrolyte for dye-sensitized solar cells. The operation of the traditional redox quasi-solid-state nanogel polymer electrolyte system is based on the I^–/I₃^– redox couple reaction with an I₂ intermediate. However, this system has issues, such as solvent leakage, low voltage, and color limitation, because the iodide-based components are in a relatively fluidic state. For addressing the durability issue, we employed ZIF-67 nanoparticles to form a quasi-solid-state electrolyte. Additionally, the ZIF-67 nanoparticles were partially decomposed into cobalt ions, which provided an additional Co²⁺/Co³⁺ redox couple system for operating the electrolyte system with the binary redox shuttle. The ZIF-67 nanoparticles reduced the polymer chain crystallinity, increasing the ion conductivity. In contrast, the tetrahedral coordinated cobalt ions in the framework, and dissociated cobalt ions absorbed visible light, leading to a loss of electron excitation. Thus, the current density decreased slightly. Nevertheless, the Co²⁺/Co³⁺ redox couple provided a modified electron level for the binary redox couple system, significantly enhancing the open-circuit voltage. Regarding practical significance, with tuning of the binary redox system, the binary redox-quasi-solid-state electrolyte can potentially exhibit color-tunable characteristics. Thus, the method of incorporating coordinated porous nanomaterials to form the binary redox-quasi-solid-state electrolyte can be adapted to other transparent renewable energy devices for increasing the operating voltage and enhancing the stability.