Planar-integrated single-crystalline perovskite photodetectors

Abstract

Hybrid perovskites are promising semiconductors for optoelectronic applications. However, they suffer from morphological disorder that limits their optoelectronic properties and, ultimately, device performance. Recently, perovskite single crystals have been shown to overcome this problem and exhibit impressive improvements: low trap density, low intrinsic carrier concentration, high mobility, and long diffusion length that outperform perovskite-based thin films. These characteristics make the material ideal for realizing photodetection that is simultaneously fast and sensitive; unfortunately, these macroscopic single crystals cannot be grown on a planar substrate, curtailing their potential for optoelectronic integration. Here we produce large-area planar-integrated films made up of large perovskite single crystals. These crystalline films exhibit mobility and diffusion length comparable with those of single crystals. Using this technique, we produced a high-performance light detector showing high gain (above 10(4) electrons per photon) and high gain-bandwidth product (above 10(8) Hz) relative to other perovskite-based optical sensors.

Figure 1. Film growth and characterization.

(a) Schematic of the experimental procedure: a large, sealed crystallizing dish filled with antisolvent is used to host a smaller dish containing the solution. A stirring bar is placed in the inner dish. (b) Kinetics of ISC perovskite growth: after the initial nucleation, the crystals grow until they reach each other and merge to form a continuous solid. At the interface, the lattice continuity is lost, producing one or multiple dislocations. (c) Top view and (d) cross-sectional SEM of the ISC perovskite film. The scale bar identifies a length of 50 μm. (e) Electron diffraction measurements, the scale bar identifies a unit of 2 nm⁻¹. (f) Steady-state photoluminescence and absorption. Inset: calculation of the optical bandgap using the Tauc method. The optical bandgap is measured to be E_g=2.24 eV.

Figure 2. Current-voltage (IV) trace and lifetime measurements.

(a) IV characteristic of the MAPbBr₃ ISC perovskites showing an ohmic region followed by trap filling region starting at V_TFL=0.3 V. From these data, we extract a conductivity σ=2 × 10⁻⁸ (Ω cm)⁻¹ and a density of trap states n_trap=2 × 10¹¹ cm⁻³. (b) PL time decay trace at λ=560 nm, with bi-exponential fits showing a fast (7±1 ns) and a slow transient (189±10 ns).

Figure 3. Photodetector based on ISC film.

(a) Three-dimensional illustration of the photodetector: the MAPbBr₃ ISC perovskite layer (orange) is deposited on top of the ITO contacts (light blue). The detector lay on a glass substrate (transparent grey). (b) Energy diagram of the photodetector. (c) Current–voltage characteristic measured in dark condition and (d) under different light power illumination, the colour bar is logarithmic.

Figure 4. Performance of the photodetector based on ISC film.

(a) Responsivity and gain (external quantum efficiency) of the photodetector. The device exhibited high and flat response for all the absorbed light frequency. (b) Transient photocurrent of the photodetector as a function of incident light power (1.1, 2.2 and 3.8 μW for the blue, brown and red trace, respectively). (c) The fall time of the photodetector is measured to be ∼25 μs.