Sachs Michael, Harnett-Caulfield Liam, Pastor Ernest, Davies Bernadette, Sowood Daniel J C, Moss Benjamin, Kafizas Andreas, Nelson Jenny, Walsh Aron, Durrant James R
Department of Chemistry and Centre for Processable Electronics, Imperial College London, London, UK.
Department of Physics and Centre for Processable Electronics, Imperial College London, London, UK.
Nat Chem. 2025 Jul 2. doi: 10.1038/s41557-025-01868-y.
Efficient sunlight-to-energy conversion requires materials that can generate long-lived charge carriers upon illumination. However, the targeted design of semiconductors possessing intrinsically long lifetimes remains a key challenge. Here using a series of transition metal oxides, we establish a link between carrier lifetime and electronic configuration in transition metal-based semiconductors. We identify a subpicosecond relaxation mechanism via metal-centred ligand field states that compromise quantum yields in open d-shell transition metal oxides (for example, FeO, CoO, CrO and NiO), which is more reminiscent of molecular complexes than crystalline semiconductors. We found that materials with spin-forbidden ligand field transitions could partially mitigate this relaxation pathway, explaining why FeO achieves higher photoelectrochemical activity than other visible light-absorbing transition metal oxides. However, achieving high yields of long-lived charges requires transition metal oxides with d or d electronic configurations (for example, TiO and BiVO), where ligand field states are absent. These trends translate to transition metal-containing semiconductors beyond oxides, enabling the design of photoabsorbers with better-controlled recombination channels in photovoltaics, photocatalysis and communication devices.
高效的阳光到能量的转换需要材料在光照下能够产生长寿命的电荷载流子。然而，具有固有长寿命的半导体的定向设计仍然是一个关键挑战。在这里，我们使用一系列过渡金属氧化物，在基于过渡金属的半导体中建立了载流子寿命与电子构型之间的联系。我们通过以金属为中心的配体场态确定了一种亚皮秒级的弛豫机制，这种机制会降低开放d壳层过渡金属氧化物（例如FeO、CoO、CrO和NiO）中的量子产率，这更让人联想到分子配合物而非晶体半导体。我们发现具有自旋禁阻配体场跃迁的材料可以部分减轻这种弛豫途径，这解释了为什么FeO比其他可见光吸收过渡金属氧化物具有更高的光电化学活性。然而，要实现长寿命电荷的高产率，需要具有d⁰或d¹⁰电子构型的过渡金属氧化物（例如TiO₂和BiVO₄），其中不存在配体场态。这些趋势适用于氧化物以外的含过渡金属的半导体，从而能够在光伏、光催化和通信设备中设计出具有更好控制的复合通道的光吸收体。
