InGaP/GaAs/InGaAs Multijunction Flexible Photovoltaics With Chemical Robustness and Radiation Hardness for Unassisted Electrocatalysis and Space Applications

ABSTRACT Monolithic III–V multijunction photovoltaics are promising candidates for both space power systems and solar‐to‐chemical energy conversion, yet their deployment in flexible, chemically aggressive, and radiation‐rich environments requires simultaneous control of epitaxial quality, conformability, and barrier properties. Here, we present a flexible InGaP/GaAs/InGaAs triple‐junction platform that addresses these requirements within a single device architecture. The optimized epitaxial stack and its growth process enable almost fully relaxed subcells with low dislocation density, supporting power conversion efficiencies above 33% under AM1.5G and ∼31% under AM0, even after transferring the epitaxial stack to a thin plastic substrate to improve mechanical compliance. To ensure environmental robustness, the flexible triple‐junction cells are encapsulated with an ultrathin glass sheet that provides strong protection against aqueous and strongly alkaline conditions, as well as against high‐energy proton and electron irradiation. By exploiting the high output voltage and durability of this platform, bias‐free electrocatalysis with formate as the predominant product is demonstrated using a simple electrocatalyst configuration. These results establish a unified III–V multijunction photovoltaic architecture that couples space‐relevant efficiency, flexibility, and radiation hardness with chemical durability suitable for unassisted solar‐to‐chemical conversion, offering a versatile route toward next‐generation terrestrial and space energy systems.