Technological advancements and manufacturing progress in photovoltaics have triggered a substantial adoption of solar electricity generation to decrease greenhouse emissions. Much of this energy is still relatively more expensive than fossil fuels, and their intermittent nature of operation can lead to non-conformity with the electric grid. Battery storage, although efficient, can still struggle in extreme climates and lack long-term durability. On the other hand, the direct conversion of abundant feedstocks such as water, carbon dioxide, and nitrogen to fuels like H₂ and NH₃ using only solar energy is a promising way to achieve reliable and on-demand sustainable clean energy. The thermodynamic minimum potential required to split water at 25 °C is 1.23 V. However, due to the kinetics of the hydrogen and oxygen evolution reactions, unassisted solar water-splitting requires a minimum potential difference of 1.6-1.7 V.

Integrated photoelectrochemical cells (PEC) require coupling photo-absorbers with anti-corrosion barriers and electrocatalysts to drive electrochemical reactions without external potential. State-of-the-art conventional III-V based PEC platforms are practically limited due to the use of cost-prohibitive semiconductors. PECs based on other semiconductors such as metal oxides (e.g., BiVO4, hematite, and copper oxide) offer scalable and low-cost solutions but exhibit Solar-to-Hydrogen (STH) efficiencies below 10% and overall low stabilities. Halide perovskites are hybrid organic-inorganic semiconductors that can produce >1V open-circuit voltage and high photocurrents up to 25mA/cm², making them ideal for interfacing two cells in series for unassisted water splitting. Here, we report a novel design strategy for an anti-corrosion barrier that enables seamless integration and conversion of any photoabsorber with the catalyst to a photoelectrochemical reactor. The conductive adhesive barrier, or CAB, is a bilayer barrier composed of a highly conductive yet inert, impermeable material that translates >99% of photoelectric energy to chemical reactions.

First, we demonstrate a photoanode-photocathode series co-planar system using p-i-n and n-i-p perovskite solar cells coupled with CAB-catalysts for unassisted water splitting with >13% STH. Post reaction current-voltage measurements on the photovoltaics revealed that the stability of the co-planar device was limited to 20h due to the hygroscopic hole transport layer. We, therefore, switched to a 28% photocurrent efficiency monolithic Si-Perovskite tandem device that can provide 1.8V open-circuit voltage, capable of driving the water-splitting reaction on its own. The Si-Perovskite tandem coupled with CAB + Ir OER catalyst achieved unassisted water splitting with a peak STH of >20% and a lifetime of over 100 hours. Briefly, we have demonstrated that the CAB achieves a near-perfect translation of photoelectric power to chemical energy for both series co-planar and monolithic architectures, enabling high efficiency and stability toward unassisted solar water-splitting. This technology will enable the production of new arbitrary solar fuels with high efficiency and durability.