Overcoming the Trade-Off between Optical Transmittance and Areal Capacitance of Transparent Supercapacitors for Practical Application.

It is substantially challenging for transition metal oxide nanoparticle (NP)-based electrodes for supercapacitors to achieve high transparency and large capacity simultaneously due to the inherent trade-off between optical transmittance (T) and areal capacitance (C A ). This study demonstrates how this trade-off limitation can be overcome by replacing some electrode NPs with transparent tin oxide (SnO 2 ) NPs. Although SnO 2 NPs are non-capacitive, they provide effective paths for charge transport, which simultaneously increase the C A and T 550nm of the manganese oxide (Mn 3 O 4 ) NP electrode from 11.7 to 13.4 mF cm -2 and 82.1% to 87.4%, respectively, when 25 wt% of Mn 3 O 4 are replaced by SnO 2 . The obtained C A values at a given T are higher than those of the transparent electrodes previously reported. An energy storage window fabricated using the mixed-NP electrodes exhibits the highest energy density among transparent supercapacitors previously reported. The improved energy density enables the window to operate various electronic devices for a considerable amount of time, demonstrating its applicability in constructing a reliable and space-efficient building-integrated power supply system.