LAUSR

Solar energy has seen 180 years of development since the discovery of the photovoltaic effect, having achieved the most successful commercialization in the energy harvesting fields. Despite its long history, even the most state-of-the-art photovoltaics remain confined to solid-state devices, limiting spatial and light utilization efficiencies. Herein, we demonstrate a liquid-state photoenergy harvester based on a photoacid, a chemical that releases protons upon light irradiation and recombines with them in the dark through a fully reversible reaction. Asymmetric light exposure on a photoacid solution contained in a transparent tube generated a pH gradient (ΔpH = 2) along the exposed and dark regions, which charges the Nernst potential up to 0.7 V across the two electrodes embedded at each end, as if a capacitor. Owing to the reversibility of photoacids, a photoacid-driven liquid-state photoenergy harvester (PLPH) generates capacitive currents up to 0.72 mA/m2 on an irradiation. Notably, the transparent nature of the PLPH enables vertical stacking up to 25 units, which multiplied the light harvesting efficiencies by over 1000%. This unique approach provides a new route to harness solar energy with a form-factor-free design that maximizes spatial and light-use efficiencies. This article is protected by copyright. All rights reserved.