Engineering halide perovskite-based buried junction photocathodes for hydrogen evolution Vishal Jose 1,2,3* , Samira Haddadi Gharamaleki 1,2,3,4 , Htoo Thiri Htet 1,2,3 , Amit Kumar Harit 1,2,3 , Anurag Krishna 1,2,3 , Tom Aernouts 1,2,3 , and Bart Vermang 1,2,3 1 Imec, imo-imomec, Thor Park 8320, 3600 Genk, Belgium, 2 EnergyVille, imo-imomec, Thor Park 8320, 3600 Genk, Belgium, 3 Hasselt University, imo-imomec, Martelarenlaan 42, 3500 Hasselt, Belgium, 4 Sapienza University of Rome,Piazzale Aldo Moro, 5, 00185 Roma RM, Italy *Email: vishal.kakkarakunneljose@imec.be Solar-driven photo(electro)catalysis systems, inspired by the process of natural photosynthesis, facilitate the spontaneous generation of high-energy-density and value-added chemical fuels from water or CO 2 . This innovative approach has the potential to enable low-cost, off-grid hydrogen or chemical production with a minimal environmental impact. Despite significant advancements, many photoelectrochemical systems for hydrogen generation continue to face challenges such as low solar-to-hydrogen efficiencies, inadequate system stability, and modularity issues. Recently, buried junction photoelectrochemical systems, where photo-absorbers are protected by a barrier material coated with catalytically active particles, have emerged as a promising solution to enhance device stability and efficiency. 1,2 Hybrid organic-inorganic halide perovskite (HAP) photo absorbers, renowned for their tunable bandgaps, extended carrier lifetimes, ambipolar charge transport, and long charge diffusion lengths on the micrometer scale, exhibit significant instability in aqueous environments. 3 Herein, we employed (Cs 0.2 FA 0.8 )Pb(I 0.95 Br 0.05 ) 3 based p-i-n configured solar cell, which was protected by a graphite sheet and epoxy, as a photocathode for the hydrogen evolution reaction. The graphite sheet (GS) played a vital role in facilitating the effective transport of photogenerated charges to the device's surface. To enhance catalytic activity, we photo-electrodeposited Pt-based hydrogen evolution catalysts (Pt) onto the graphite sheets. The key layers were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ultimately, the fabricated p-i-n HAP-GS-Pt device demonstrated a current density of 20 mA/cm² at a potential of 0.4 V vs. RHE and an onset potential of 1.1 V vs. RHE in a 1 M KOH electrolyte. Further, this electrode maintained its initial photocurrent density for over 2 hours of continuous operation. Later, the p-i-n HAP-GS-Pt photoelectrode was seamlessly integrated with a BiVO4/FeOOH photoanode, resulting in an artificial leaf system capable of performing unassisted solar water splitting. This device achieved a solar-to-hydrogen efficiency of nearly 2% with a continuous 3-hour operation in a slightly alkaline solution. This work highlights the potential of buried junction photoelectrochemical cells to enable artificial leaf systems that are both modular and stable. References 1. Sivula, K. Photoelectrochemical Solar Fuels: What’s Next? ACS Energy Letters vol. 10 2877–2879m(2025). 2. Crespo-Quesada, M. et al. Metal-encapsulated organolead halide perovskite photocathode for solar-driven hydrogen evolution in water. Nat Commun 7, (2016). 3. Fehr, A. M. K. et al. Integrated halide perovskite photoelectrochemical cells with solar-driven water-splitting efficiency of 20.8%. Nat Commun 14, 3797 (2023).
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