Solar cell-coupled metallo-supramolecular polymer-based electrochromic device in renewable energy storage and on-demand usage

Abstract

Herein we report application of a surface-coated [Fe(terpyridine) 2 ] 2+ -containing metallo‐supramolecular polymer (MSP) in fabricating rechargeable bifunctional electrochromic energy-storage devices which were coupled with commercial silicon solar cell to demonstrate integrated solar energy harvesting, storage and utilization. The best MSP, {Fe 1.5 L1} n , chosen for the device-fabrication, evolved through a prior systematic structure-property investigation involving three similar but structurally fine-tuned polymers {Fe 1.5 L1} n , {Fe 1.5 L2} n , and {Fe 1.5 L3} n . The difference in the three-dimensional propagation and porosity of the {Fe 1.5 L1} n system from the other two polymers, resulted in its excellent spectroelectrochemical properties on indium-tin oxide (ITO) surface at an active-layer thickness of 345 nm. The fabricated five-layered solid-state electrochromic device (ECD) with this system, in the presence of solar energy, exhibited fast switching time (t = 1.2 s for coloration and 2.2 s for bleaching), high optical contrast (ΔT = 47%), high open-circuit charge-retention time (t 50% = 193 min), and excellent cyclic stability (up to 10,000 cycles). The promising property of the device was attributed to the presence of a large excess of counter anions associated to the imidazolium moieties at the vicinity of the redox-active Fe sites of the polymer to stabilize the Fe(III) state efficiently by balancing the overall charge. Further, the device was used as a charge-storage material by connecting several devices in a series, and it was able to (i) power on a 3.5 V light-emitting diode (LED) bulb, (ii) run a 1.7 V digital thermo-hygrometer, and (iii) run a 3 V multimeter for 3 s, 40 s and 3 s respectively. Finally, switching of a 6 cm × 4 cm flexible ITO|PET-based EC device (PET = polyethylene terephthalate) was performed under bent condition using solar energy, and in the charged state, it was able to run a thermo-hygrometer for more than 2 min. This work unveils the hitherto unexplored opportunity to couple MSP-based ECD with solar-cell device (SCD) for solar energy storage and on-demand usage. • A surface-coated [Fe(terpy) 2 ] 2+ -containing polymer was generated with a tris-imidazolium-based tris-terpy ligand. • This material was employed to fabricate a rechargeable bifunctional electrochromic energy-storage device. • Commercial silicon solar cell was coupled to it demonstrating integrated solar energy harvesting, storage and on-demand utilization. • This work unveils the hitherto unexplored opportunity to couple MSP-based electrochromic device with solar-cell device.