Artificial leaves could be the breakthrough technology to overcome the limitations of storage and mobility through the synthesis of chemical fuels from sunlight, which will be an essential component of a sustainable future energy system. However, the realization of efficient solar-driven artificial leaf structures requires integrated specialized materials such as semiconductor absorbers, catalysts, interfacial passivation, and contact layers. To date, no competitive system has emerged due to a lack of scientific understanding, knowledge-based design rules, and scalable engineering strategies. Herein, competitive artificial leaf devices for water splitting, focusing on multiabsorber structures to achieve solar-to-hydrogen conversion efficiencies exceeding 15%, are discussed. A key challenge is integrating photovoltaic and electrochemical functionalities in a single device. Additionally, optimal electrocatalysts for intermittent operation at photocurrent densities of 10–20 mA cm−2 must be immobilized on the absorbers with specifically designed interfacial passivation and contact layers, so-called buried junctions. This minimizes voltage and current losses and prevents corrosive side reactions. Key challenges include understanding elementary steps, identifying suitable materials, and developing synthesis and processing techniques for all integrated components. This is crucial for efficient, robust, and scalable devices. Herein, corresponding research efforts to produce green hydrogen with unassisted solar-driven (photo-)electrochemical devices are discussed and reported.

The authors express gratitude for financial support provided by the German Federal Ministry of Education and Research (H2Demo project no. 03SF0619 and DEPECOR project no. 10033RC021) and German Research Foundation (DFG project PAK 981, project nos. HA3096/14-1, JA859/35-1, RU1383/6, KR4816/1-1; NSF-DFG project no. HA3096/19-1). W.J. acknowledges additionally the support by DFG priority programme 1613, Ja 859/26-1, and Ja 859/26-2, and Excellency graduate school DFG GSC 1070. The authors acknowledge Juliane Koch for provid- ing the material used in Figure 25