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Spray-Coating Thick Films of All-Inorganic Halide Perovskites for Filterless Narrowband Photodetectors.

A significant challenge facing perovskite narrowband photodetectors is making high-quality and thick enough films. Here, we report a facile one-step spray-coating approach to deposit cesium lead halide perovskite thick films for filterless narrowband photodetectors, which exhibited a specific detectivity of 2.43 × 1010 Jones at 655 nm with an fwhm of 25 nm. We demonstrated that both substrate temperature and deposition time during the spray-coating process are key factors that govern the thickness and morphology of perovskite films. The photodetection behavior was dependent on the film thickness, and the narrowband photoresponse was recorded at a 3.9 μm thickness. We discovered that the internal electric field also plays a critical role in determining the narrowband photoresponse behavior. A distinct photoresponse behavior was observed when respectively applying a reverse bias and a forward bias, which is ascribed to the trade-off between the charge-trapping effect and charge extraction under the internal built-in electric field in different biased conditions. Through changing the halogen composition of perovskites from CsPbCl2Br to CsPbI2Br, the peak position of the narrowband spectral photoresponse was observed to shift from 460 to 660 nm. This study not only offers a controllable spray-coating approach to develop thick perovskite films but also provides an important guidance for the rational design of filterless narrowband photodetectors for practical applications in industrial control, visual imaging, and biological sensing.