Sensitive, High-Speed, and Broadband Perovskite Photodetectors with Built-In TiO₂ Metalenses

Monolithic integration of nanostructured metalenses with broadband light transmission and good charge transport can simultaneously enhance the sensitivity, speed, and efficiency of photodetectors. The realization of built-in broadband metalenses in perovskite photodetectors, however, has been largely challenged by the limited choice of materials and the difficulty in nanofabrication. Here a new type of broadband-transmitting built-in TiO₂ metalens (meta-TiO₂) is devised, which is readily fabricated by one-step and lithograph-free glancing angle deposition. The meta-TiO₂, which comprises of sub-100 nm TiO₂ nanopillars randomly spaced with a wide range of sub-wavelength distances in 5–200 nm, shows high transmittance of light in the wavelength range of 400–800 nm. The meta-TiO₂ also serves as an efficient electron transporting layer to prevent the exciton recombination and facilitate the photoinduced electron extraction and transport. Replacing the conventional mesoporous TiO₂ with the meta-TiO₂ comprehensively leads to enhancing the detection speed by three orders of magnitude to a few hundred nanoseconds, improving the responsivity and detectivity by one order of magnitude to 0.5 A W⁻¹ and 10¹³ Jones, respectively, and extending the linear dynamic range by 50% to 120 dB.