Electrolyte additive strategy for uniform nucleation of Cu–Bi toward low-voltage self-powered dynamic windows

Abstract

Reversible metal electrodeposition devices (RMEDs) powered by solar cells have shown promise in energy-saving buildings. However, the high driving voltage and unclear nucleation/growth mechanism of metal particles have hindered their application. Herein, we propose an electrolyte additive strategy to lower the driving voltage and develop an integrated RMED, where Cu–Bi RMED is driven by CsPbI₂Br solar cells. Results confirm that our integrated device can achieve a fast chromatic transition from transparent to black only under sunlight, displaying 62.42% optical contrast and outstanding performance durability. Studies on the dynamic nucleation mechanism reveal that the introduction of choline chloride (ChCl) in water can provide more theoretical nucleation sites (from 4.94 to 13.55 μm⁻²) and facilitate an easier electrodeposition process, resulting in uniform/dense bimetallic films. Experimental results indicate that the ionic conductivity increases from 0.05 to 0.31 S m⁻¹, and the charge transfer resistance decreases from 3834 to 647 Ω cm² upon the introduction of ChCl, leading to fast nucleation and color-change at low driving voltage. Furthermore, CsPbI₂Br solar cells, with an open-circuit voltage of up to 1.32 V, guarantee smooth operation of the integrated device via Pb(Ac)₂ modification and L-phenylalanine (L-PAA) passivation. Hence, the application limitations of RMED might potentially be overcome by introducing appropriate electrolyte strategies.