All-Perovskite Tandem Photoelectrodes for Unassisted Solar Hydrogen Production

Unassisted solar water splitting by multijunction tandem photoelectrodes is a sustainable approach to generating green hydrogen fuels. Here, we report on the fabrication of monolithically integrated all-perovskite tandem photocathodes for efficient unassisted solar water splitting. All-perovskite tandem photocathodes wired to an iridium oxide anode deliver a high photovoltage of more than 2 V with an operating photocurrent density of 12.5 mA cm^-2 at zero applied bias under simulated AM1.5G 1 sun illumination, yielding a solar-to-hydrogen (STH) conversion efficiency of 15%. The tandem photoelectrode demonstrates continuous operation in water for more than 120 h under simulated 1 sun illumination with less than 5% efficiency loss. A technoeconomic analysis shows the projected production cost of all-perovskite tandem photoelectrodes is $30 m^-2, promising a levelized cost of hydrogen of less than $1/kg if sufficient device longevity is realized. This work provides a path toward achieving cost-effective unassisted solar hydrogen fuel production.