Polarization-sensitive photodetection in a broad spectrum range is highly desired due to the great significance in military and civilian applications. Palladium diselenide (PdSe2), a newly explored air-stable, group 10 two-dimensional (2D) noble metal dichalcogenide with a puckered pentagonal structure, holds promise for polarization-sensitive photodetection. Herein, we report a highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction. Owing to the enhanced light absorption of the mixed-dimensional van der Waals heterojunction and the effective carrier collection with graphene transparent electrode, the photodetector exhibits superior device performance in terms of a large photoresponsivity, a high specific detectivity, a fast response speed to follow nanosecond pulsed light signal, and a broadband photosensitivity ranging from deep ultraviolet (DUV) to mid-infrared (MIR). Significantly, highly polarization-sensitive broadband photodetection with an ultrahigh polarization sensitivity of 112.2 is achieved, which represents the best result for 2D layered material-based photodetectors. Further, we demonstrated the high-resolution polarization imaging based on the heterojunction device. This work reveals the great potential of 2D PdSe2 for high-performance, air-stable, and polarization-sensitive broadband photodetectors.

2D transition‐metal dichalcogenides (TMDs), which exhibit fascinating and fantastic properties, have promising applications in future electronic devices and photoelectric devices. Here, the recent research on 2D TMDs is summarized, including single components, 2D doped TMDs, and 2D van der Waals heterostructures. The physical picture, synthetic methods, and optoelectronic properties of these 2D materials are comprehensively described. Opportunities and emerging applications of 2D materials in the future are briefly discussed.

graphene, however, is problematic for many optoelectronic applications. Semiconducting layered metal dichalcogenides (LMDs) have generated an immense amount of interest, owing to their specific bandgaps in the ≈1-2.4 eV range. [2] Most LMDs undergo a transition from an indirect bandgap material in the multilayer form to a direct bandgap material in the monolayer form and exhibit strong lightmatter interaction at the 2D limit. [3,4] All of these features make 2D LMDs promising materials for several applications, such as transistors [5] and optoelectronic [6] and valleytronic [7] devices. Nonetheless, the finite bandgap of such reported LMDs largely restricts their applications in IR and ultraviolet (UV) photodetection. [8] UV photodetection, particularly in the solar blind range (200 to 280 nm), has great potential in the missile detection, flame alarms, and so forth. However, the lack of wide bandgap LMD materials makes realizing 2D UV photodetectors a challenge.As a new important member of the LMD family, germanium diselenide (GeSe 2 ), with a direct wide bandgap, has many potential applications in UV detection and IR waveguides. [9] Moreover, GeSe 2 exhibits a monoclinic crystal structure, [10] within two crystallographically different types of GeSe 4/2 tetrahedra centered on the Ge1 and Ge2 atoms, as shown in As an important 2D layered metal dichalcogenide, germanium diselenide (GeSe 2 ) with a direct wide bandgap is attracting increasing attention for its potential applications in ultraviolet (UV) detection. However, only few-layer GeSe 2 has been reported to date. Here, a joint theoretical-experimental study on the optical and electronic properties of monolayer GeSe 2 is presented, and monolayer GeSe 2 is shown to have a direct wide bandgap of 2.96 eV. Consequently, monolayer GeSe 2 does not respond to a major fraction of the visible spectrum. Notably, the photofield effect transistors based on the GeSe 2 monolayer show p-type behavior, high responsivity, superior detectivity, and a fast response time, competitive with state-of-the-art UV detectors. In addition to the excellent photoresponse properties, 2D GeSe 2 crystals also exhibit perpendicular optical reversal of the linear dichroism and polarized photodetection under wavelength modulation. Theoretical calculations of the band structure are used to shed light on these experimental results. The findings suggest that 2D GeSe 2 is a promising candidate for highly selective polarization-sensitive UV detection.

Type-II band alignment, a suitable direct gap (1.519 eV), superior optical-absorption (∼105) and a broad spectrum make the GeSe/SnS heterobilayer a promising material for photovoltaic applications.

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