Oxygen vacancies (OVs) are a mixed blessing for the photoelectrochemical (PEC) water oxidation performance of monoclinic tungsten trioxide (m-WO 3 ) photoanodes. Although it is widely accepted that a moderate concentration of OVs is beneficial for the PEC performance of the m-WO 3 photoanodes, this argument assumes a uniform distribution of OVs throughout the m-WO 3 crystal. In this case, only the overall concentration of OVs needs to be considered. However, the spatial non-uniformity of OV defects in m-WO 3 photoanodes has not been thoroughly examined. In this study, by employing a m-WO 3 nanorod array as a model photoanode, the aim is to show that a higher OV concentration near the surface of m-WO 3 compared to that in the bulk is advantageous for the PEC performances of this material. In addition, a laser-assisted defect control (LADC) process is employed to manipulate the spatial distribution of OVs in the m-WO 3 photoanodes to achieve enhanced PEC performances. Moreover, a one-step laser deposition process is introduced to obtain an ultrathin FeNi oxygen evolution catalyst overlayer on the defect-controlled m-WO 3 photoanodes, further improving PEC performance, photostability, and Faradaic efficiency.

design of vertically stacked diode-type photodetectors (PDs) resembling the Foveon structure. [1,2] The Foveon PDs based on Si diodes were introduced in late 1999 as an alternative to the most widely used Bayer-type PDs. [3] The former consists of vertically stacked three individual detectors, which selectively absorb incident blue/green/red light along the depth of light penetration in a single pixel. In contrast, the latter consists of laterally arrayed detectors underneath dissipative color filters of blue/green/green/red where a single pixel includes a package of lateral four color filters. [4] Therefore, a vertically staked PD reduces photon loss caused by a color filter, as much as two-thirds of the total light flux in the Bayer PDs, and enables ultra-miniaturization for spatial integration. [1] However, the Foveon structure has poor detection ability for blue light, which is attributed to low absorption coefficients of Si due to its indirect transition nature. [2] A thick (≈10 µm) Si layer is required for the Foveon type because of the low absorption coefficients, which results in lengthy diffusion path, thus a low quantum efficiency in the blue region owing to severe A self-powered, color-filter-free blue photodetector (PD) based on halide perovskites is reported. A high external quantum efficiency (EQE) of 84.9%, which is the highest reported EQE in blue PDs, is achieved by engineering the A-site monovalent cations of wide-bandgap perovskites. The optimized composition of formamidinium (FA)/methylammonium (MA) increases the heat of formation, yielding a uniform and smooth film. The incorporation of Cs + ions into the FA/MA composition suppresses the trap density and increases charge-carrier mobility, yielding the highest average EQE of 77.4%, responsivity of 0.280 A W −1 , and detectivity of 5.08 × 10 12 Jones under blue light. Furthermore, Cs + improves durability under repetitive operations and ambient atmosphere. The proposed device exhibits peak responsivity of 0.307 A W −1 , which is higher than that of the commercial InGaN-based blue PD (0.289 A W −1 ). This study will promote the development of next-generation image sensors with vertically stacked perovskite PDs.

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