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Abstract Catalytic interface of semiconductor photoelectrodes is critical for high-performance photoelectrochemical solar water splitting because of its multiple roles in light absorption, electrocatalysis, and corrosion protection. Nevertheless, simultaneously optimizing each of these processes represents a materials conundrum owing to conflicting requirements of materials attributes at the electrode surface. Here we show an approach that can circumvent these challenges by collaboratively exploiting corrosion-resistant surface stoichiometry and structurally-tailored reactive interface. Nanoporous, density-graded surface of ‘black’ gallium indium phosphide (GaInP₂), when combined with ammonium-sulfide-based surface passivation, effectively reduces reflection and surface recombination of photogenerated carriers for high efficiency photocatalysis in the hydrogen evolution half-reaction, but also augments electrochemical durability with lifetime over 124 h via strongly suppressed kinetics of corrosion. Such synergistic control of stoichiometry and structure at the reactive interface provides a practical pathway to concurrently enhance efficiency and durability of semiconductor photoelectrodes without solely relying on the development of new protective materials. 

Abstract Inverted metamorphic (IMM) multijunction solar cells represent a promising material platform for ultrahigh efficiency photovoltaic systems (UHPVs) with a clear pathway to beyond 50% efficiency. The conventional device processing of IMM solar cells, however, typically involves wafer bonding of a centimeter‐scale die and destructive substrate removal, thereby imposing severe restrictions in achievable cell size, type of module substrate, spatial layout, as well as cost effectiveness. Here, we report material design and fabrication strategies for microscale triple‐junction IMM (3J IMM) Ga_0.51In_0.49P/GaAs/In_0.26Ga_0.74As solar cells that can overcome these difficulties. Specialized schemes of delineation and undercut etching enable the defect‐free release of microscale IMM solar cells and printed assemblies on a glass substrate in a manner that preserves the growth substrate, where efficiencies of 27.3% and 33.9% are demonstrated at simulated AM1.5D one‐ and 351 sun illumination, respectively. A composite carrier substrate where released IMM microcells are formed in fully functional, print‐ready configurations allows high‐throughput transfer printing of individual IMM microcells in a programmable spatial layout on versatile choices of module substrate, all desired for CPV applications.