Researchers from China's Jilin University have designed a spray coated spherical perovskite photonic sensor made of phenyl ethyl ammonium/formamidinium lead halide (PEA2FAn-1PbnX3n+1). The researchers utilized the perovskite formulations to regulate the crystallization rate. Cyclic spray-coating and the solution concentration were used to control the coating thickness from a few nanometers to hundreds of micrometers.
Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required in order to meet the fast development pace of modern technology. However, it remains challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. In this recent study, the team demonstrated the feasibility of using a rapid spray-coating procedure to fabricate perovskite hemispherical photodetectors that can execute lens-free scanning at nearly 180°, considerably decreasing the reliance on complex optical components.
For consistent layer thickness, the substrate was rotated during spray coating. Before deposition, hemispherical platforms with thoroughly cleansed edges were placed on a hot plate. High-speed nitrogen (N2) gas was used to exfoliate the surfaces and expedite the crystallization of the coatings. To enhance crystallization quality, the sheets were ultimately thermally treated. The films' surfaces were refined to create a smooth and compact coating with minimal surface flaws. Chromium (Cr) electrodes were mounted on commercialized hemispherical glass substrates to increase surface adherence to build a hemispherical device.
The poor conductance of the bottom Cr electrodes contributed to a lower cut-off ratio of hemispherical devices when compared to planar devices. The photocurrent of the device was measured about the incident light angle to investigate the wide-angle detection accuracy.
Upon diverse light incidence angles between 0° and 90°, the hemispherical sensor displayed autonomous photon energy. However, because of the restricted light absorption at slanted orientations, the photocurrent of the planar sensor proportionally reduced with the incident angle.
A model of a swan was used for imaging studies. A clear image of a swan was captured in the right panel when the object was placed at a viewing angle between 90° and -52°. The image had the same viewing angle range of -8° to 30° and had a spatial resolution of 1.78 lp mm-1. The benefits of a hemispherical photocell are shown by the fact that the planar device completely lost signal at a viewing angle of about 90 degrees and could only capture a half-image of the swan.