Two-Dimensional Cs₂AgBiBr₆/WS₂ Heterostructure-Based Photodetector with Boosted Detectivity via Interfacial Engineering

Abstract

Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers have been widely used for optoelectronic devices because of their ultrasensitivity to light detection acquired from their direct gap properties. However, the small cross-section of photon absorption in the atomically thin layer thickness significantly limits the generation of photocarriers, restricting their performance. Here, we integrate monolayer WS2 with 2D perovskites Cs2AgBiBr6, which serve as the light absorption layer, to greatly enhance the photosensitivity of WS2. The efficient charge transfer at the Cs2AgBiBr6/WS2 heterojunction is evidenced by the shortened photoluminescence (PL) decay time of Cs2AgBiBr6. Scanning photocurrent microscopy of Cs2AgBiBr6/WS2/graphene reveals that improved charge extraction from graphene leads to an enhanced photoresponse. The 2D Cs2AgBiBr6/WS2/graphene vertical heterostructure photodetector exhibits a high detectivity (D*) of 1.5 × 1013 Jones with a fast response time of 52.3 μs/53.6 μs and an on/off ratio of 1.02 × 104. It is worth noting that this 2D heterostructure photodetector can realize self-powered light detection behavior with an open-circuit voltage of ∼0.75 V. The results suggest that the 2D perovskites can effectively improve the TMDC layer-based photodetectors for low-power consumption photoelectrical applications.

Air‐Stabilized Lead‐Free Hexagonal Cs3Bi2I9 Nanocrystals for Ultrahigh‐Performance Optical Detection

“…Based the aforementioned results, the high performance and fast response of the vertical-structured device are probably originated from the large built-in electric field at p-n junction with short photogenerated carrier transport path [20] and the high conductivity of the graphene electrode. [41,51] The vague energy diagrams of p-Si/Cs 3 Bi 2 I 9 system in thermal equilibrium and at reverse bias are illustrated in Figures 5d and 5e, respectively. In detail, the Fermi energy levels of p-Si and Cs 3 Bi 2 I 9 are equal at thermal equilibrium of the p-n heterojunction, and a depletion layer forms at the interface, resulting in the emergence of a built-in electric field (Figure 5d).…”

“…To understand the effect of graphene on our device, the Schottky barrier (Φ SB ) of the Cs 3 Bi 2 I 9 /graphene junction, Φ SB = Φ Gr − χ, can be calculated to be 0.3 eV in the dark, where Φ Gr is graphene's work function and χ is the electron affinity of Cs 3 Bi 2 I 9 . [ 51 ] Under illumination, the photogenerated electrons are transferred and collected by graphene top electrode to reduce the graphene's work function. [ 52 ] Thus, the contact resistance of the Cs 3 Bi 2 I 9 /graphene Schottky junction tuned to lower, resulting in efficient charge transfer between Cs 3 Bi 2 I 9 layers and graphene electrodes (Figure 5f).…”

A solution-fabricated tellurium/silicon mixed-dimensional van der Waals heterojunction for self-powered photodetectors

“…On the other hand, responsivity (R) and specific detectivity (D*) stand for the capacity of the photoelectric conversion efficiency in the photodetector and the capability to detect weak light signals, respectively. They can be modeled as 29,52…”

“…On the other hand, responsivity ( R ) and specific detectivity ( D *) stand for the capacity of the photoelectric conversion efficiency in the photodetector and the capability to detect weak light signals, respectively. They can be modeled as 29,52 andwhere S reflects the effectively illuminated area ( S = 207 μm 2 ), and S n is the noise spectral density calculated by the Fourier transformation of the dark current trace (Fig. S9b, ESI†).…”

“…In recent years, all-2D self-powered photodetectors with various device structures have been successively reported with stunning properties such as gate-tunability, wide-range photodetection, and other potentially new functionalities. [27][28][29] However, it remains a daunting challenge to control doping types, carrier concentrations, and chemical ratios for most 2D materials and their heterojunctions, which severely impedes the range and progression of full 2D vdWH. 22 Alternatively, high-quality mixed-dimensional vdWH integrated on commercially available semiconductors, for example, Si, Ge, GaN, GaAs, etc., may endow the device with coupling properties and provide a feasible avenue for enhancing photoelectric performances.…”