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Photodiode‐type solar‐blind photodetectors (SBPDs) with the self‐powered feature hold great promise for applications in unattended secure communication, flame detection, and missile warning. However, the responsivity of SBPDs is usually limited due to the severe solar‐blind (SB) light extinction in substrates and charge transport layers. Herein, a spectrally selective hole extraction structure (SHE) is proposed for high‐efficiency perovskite SBPDs. The SHE consisting of a tandem Fabry–Perot cavity and energy‐level‐matched hole transport layer endows the device with narrowband absorption in the SB region and optimized charge extraction capability from the CsPbI2Br perovskite. The optimized SHE exhibits a peak transmittance of 27% at 255 nm and a half maximum at full width of 28 nm. Under SB light illumination, the champion device achieves a responsivity of 56.20 mA W−1 and a detectivity (D*) of 2.86 × 1013 Jones, which are the record values among the reported results. The approach demonstrated here paves the way for the optical and electrical design of perovskite photodetectors with spectrally selective detection. [ABSTRACT FROM AUTHOR]

New two‐dimensional (2D) van der Waals materials are emerging, and their optical parameters urgently need to be acquired experimentally. Most of the reported results come from traditional metrologies used in the past for bulk materials. This unavoidably causes controversy regarding the correctness and accuracy of results, as well as the physical model. Surface/interface plasmon polariton waves are sub‐diffraction‐limited and very sensitive to surroundings. Here, 2D van der Waals materials with metal embodied are presented. Surface/interface exciton‐plasmon polaritons come into being with excitons in 2D transition‐metal dichalcogenides (TMDCs), which are physically taken as the boundary conditions with complex optical conductivities at the interfaces. Complex optical conductivities of 2D TMDCs are measured by means of interference behavior of surface/interface polariton waves. The size requirement of 2D van der Waals materials becomes relaxed, and complex optical conductivities can be measured for single‐crystalline WS2 and MoS2 monolayers with small sizes. Furthermore, a remarkable capability is manifested by yielding complex optical conductivity of van der Waals heterostructures. The proposed metrology can apply to other newly developed materials with modified underlying physical models, as well as various types of 2D van der Waals materials. [ABSTRACT FROM AUTHOR]