Photocatalysts Based on Organic Semiconductors with Tunable Energy Levels for Solar Fuel Applications

The photocatalytic synthesis of solar fuels such as hydrogen and methane from water and carbon dioxide is a promising strategy to store abundant solar energy in order to overcome its intermittency. Although this approach has been studied for decades using inorganic semiconductor photocatalysts, organic semiconductors have only recently gained notable attention. The tunable energy levels of organic semiconductors can enable the design of photocatalysts with optimized solar light utilization. However, the solar conversion efficiency of organic semiconductor photocatalysts has so far been limited by their low quantum efficiencies. To address this issue, various photocatalyst design strategies including semiconductor energy level optimization, surface modification, and the fabrication of heterojunctions have been applied, resulting in substantial increases in photocatalytic efficiency. This progress report systematically describes the strategies employed to increase the efficiency of organic semiconductor photocatalysts for the generation of solar fuels from water and carbon dioxide. Particular attention is given to describing strategies to enhance quantum efficiency, and insights are provided on the mechanisms underlying their success to aid the rational design of future organic photocatalysts. Perspectives on the future challenges and promising research directions for the design of efficient organic photocatalysts for the generation of solar fuels are also provided.