Rational Design of Photoelectrochemical Perovskite-BiVO₄ Tandem Devices for Stable Fuel Production

Metal halide perovskites have emerged as promising alternatives to commonly employed light absorbers for solar fuel synthesis, enabling unassisted photoelectrochemical (PEC) water splitting^[1,3] and CO₂ reduction to syngas.^[2,4] While the bare perovskite light absorber is rapidly degraded by moisture, recent developments in the device structure have led to substantial advances in the device stability. Here, we give an overview of the latest progress in perovskite PEC devices, introducing design principles to improve their performance and reliability. For this purpose, we will discuss the role of charge selective layers in increasing the device photocurrent and photovoltage, by fine-tuning the band alignment and enabling efficient charge separation. A further beneficial effect of hydrophobicity is revealed by comparing devices with different hole transport layers (HTLs).^[1,3] On the manufacturing side, we will provide new insights into how appropriate encapsulation techniques can extend the device lifetime to a few days under operation in aqueous media.^[1,2] To this end, we replace low melting alloys with graphite epoxy paste as a conductive, hydrophobic and low-cost encapsulant.^[3,5] The combined advantages of these approaches are demonstrated in a perovskite-BiVO₄ tandem device archiving selective unassisted CO₂ reduction to syngas.^[4] These design principles are successfully applied to an underexplored BiOI light absorber, increasing the photocathode stability towards hydrogen evolution from minutes to months.^[6] Finally, we take a glance at the next steps required for scalable solar fuels production, showcasing our latest progress in terms of device manufacturing. A suitable choice of materials can decrease the device cost tenfold and expand the device functionality, resulting in flexible, floating artificial leaves.^[7] Those materials are compatible with large-scale, automated fabrication processes, which present the most potential towards future real-world applications.^[8,9] Such PEC systems approaching a m² size can further take advantage of the modularity of artificial leaves.^[10]<br/><br/>[1] Andrei, V. et al. <i>Adv. Energy Mater.</i> 2018, 8, 1801403.<br/>[2] Andrei, V.; Reuillard, B.; Reisner, E. <i>Nat. Mater.</i> 2020, 19, 189–194.<br/>[3] Pornrungroj, C.; Andrei, V et al. <i>Adv. Funct. Mater.</i> 2021, 31, 2008182.<br/>[4] Rahaman, M.; Andrei, V. et al. <i>Energy Environ. Sci.</i> 2020, 13, 3536–3543.<br/>[5] Andrei, V.; Bethke, K.; Rademann, K. <i>Phys. Chem. Chem. Phys.</i> 2016, 18, 10700–10707.<br/>[6] Andrei, V.; Jagt, R. A. et al. <i>Nat. Mater.</i> 2022, 21, 864–868.<br/>[7] Andrei, V.; Ucoski, G. M. et al. <i>Nature</i> 2022, 608, 518–522.<br/>[8] Sokol, K. P.; Andrei, V. <i>Nat. Rev. Mater.</i> 2022, 7, 251–253.<br/>[9] Andrei, V.; Roh, I.; Yang, P. <i>Sci. Adv.</i> 2023, 9, eade9044.<br/>[10] European Commission; Directorate-General for Research; Innovation. Artificial photosynthesis : fuel from the sun : EIC Horizon Prize; Publications Office of the European Union, 2022. DOI: 10.2777/682437.