Spray-coated perovskite hemispherical photodetector featuring narrow-band and wide-angle imaging

Abstract

Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA₂FA_n-1Pb_nX_3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10^-4 cm³ s^-1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.

Fig. 1. The effective incident flux intensity on hemispherical and planar surface, and thick perovskite films by spray-coating.

a Schematic diagram of the vertical component of incident light on hemispherical and planar surface. The incident light (red arrow) is decomposed into components parallel and perpendicular to the surface. ψ and φ are angles to evaluate the angle of incident light. b The simulated spatial distribution of effective incident flux incident of planar and hemispherical surface ($S_{\perp }=\pi R^2$) under incident light from 0°, 45°, and 90°. c The integrated $I_{\perp }$ flux under incident light from incident light from different angles. d Schematic diagram of the film fabrication process through spray-coating. e The XRD spectra of the perovskite film in each step of spray-coating process. f The simulation of fluid field’s velocity magnitude distribution (The angle of spray-coating is 45°) g The simulation of liquid film thickness (linear dynamic spraying: 5 cm s⁻¹) at the first second.

Fig. 2. The thick perovskite film fabricated by spray-coating and crystallization process.

a The optical photographs of spray-coated perovskite (PEA₂FA₃Pb₄I₁₃) films deposited onto different substrates of different sizes and shapes. b The SEM image of the surface of the perovskite film on hemispherical substrate. c The cross-section SEM image of the perovskite film on curved substrate. d The time history of solid film formation ratio (the crystallization processes of different perovskites). e Schematic diagram of the solid film thickness during spray-coating and N₂ flowing process. f The microscope images of the crystallization processes of different perovskites precursors drop-coated on the hot plate.

Fig. 3. The charge carriers’ transport in spray-coated thick film and narrow-band photodetector.

a Schematic diagram of the perovskites (PEA₂FA_n-1Pb_nX_3n+1) films fabricated by spray-coating. The recombination occurs at the grain boundary (2D region), selectively collecting long wavelength-generated carriers and narrow-band response. b The TRPL spectra of PEA₂FA₃Pb₄I₁₃ (τ = 33.14 ns) and FAPbI₃ (τ = 54.48 ns) fabricated by spray-coating. c The device structure to analyze the influent of narrow-band response photosensitive layer. d The EQE value of devices (film thickness: 16 μm) based on perovskites with different n value. e The EQE value of devices based on PEA₂FA₃Pb₄I₁₃ films of different thickness (2 μm, 4 μm, 8 μm, 12 μm, and 16 μm). f The μτ product of PEA₂FA₃Pb₄I₁₃ and FAPbI₃ films fabricated by spray-coating. g The charges density of PEA₂FA₃Pb₄I₁₃ film at different wavelength and positions simulated by diffusion length and absorbance spectrum. h The narrow-band response (EQE) of perovskites photodetectors with different halogen ratio (PEA₂FA₃Pb₄I₁₃, PEA₂FA₃Pb₄I₈Br₅, PEA₂FA₃Pb₄I₅Br₈, and PEA₂FA₃Pb₄Br₁₃).

Fig. 4. Narrow-band and Wide-angle imaging of a hemispherical photodetector.

a The device structure of the hemispherical photodetector. b Left: The schematic of the imaging system and the optical photo of a swan as object. Right: The images captured by hemispherical photodetectors with different I/Br ratios. The colors of images are matched to the color function. c The photocurrent of hemispherical photodetector under irradiation from different angles (The size of the light source is smaller than the area of photodetectors.). The orange line is the relationship between the theoretical normalized transmittance and the incident angle of a planar perovskite film surface. d Left: The schematic of the imaging system for wide angle detection. Right: The images captured by planar and hemispherical photodetectors based on different angles of incident light. e The schematic of the structure of the micro-array (9 × 9) device f Left: The schematic of the imaging system and the optical photo of a square plastic object. Right: The micro-array imaging result.