A deep understanding of defects is essential for the optimization of materials for solar energy conversion. This is particularly true for metal oxide photo(electro)catalysts, which typically feature high concentrations of charged point defects that are electronically active. In photovoltaic materials, except for selected dopants, defects are considered detrimental and should be eliminated to minimize charge recombination. However, photocatalysis is a more complex process in which defects can have an active role, such as in stabilizing charge separation and in mediating rate-limiting catalytic steps. In this Review, we examine the behaviour of electronic defects in metal oxides, paying special attention to the principles that underpin the formation and function of trapped charges in the form of polarons. We focus on how defects alter the electronic structure of metal oxides, statically or transiently upon illumination, and discuss the implications of such changes in light-driven catalytic reactions. Finally, we compare oxide defect chemistry with that of new photocatalysts based on carbon nitrides, polymers and metal halide perovskites.

深入了解缺陷对于优化太阳能转换材料至关重要。对于金属氧化物光（电）催化剂来说尤其如此，它通常具有高浓度的电子活性带电点缺陷。在光伏材料中，除了选定的掺杂剂外，缺陷被认为是有害的，应予以消除以最大限度地减少电荷复合。然而，光催化是一个更复杂的过程，其中缺陷可以发挥积极作用，例如稳定电荷分离和介导限速催化步骤。在这篇综述中，我们研究了金属氧化物中电子缺陷的行为，特别关注了以极化子形式捕获电荷的形成和功能的基础原理。我们专注于缺陷如何在光照下静态或瞬时改变金属氧化物的电子结构，并讨论这种变化对光驱动催化反应的影响。最后，我们将氧化物缺陷化学与基于氮化碳、聚合物和金属卤化物钙钛矿的新型光催化剂进行比较。