**1. Introduction**

Photodetectors, which can capture, identify and visualize the optical signals, have been indispensable devices in modern integrated electronics and communication technology [1–5]. Nowadays, various photosensitive materials have been investigated as the functional materials in photodetectors. For example, gallium nitride (GaN) is commercially for ultraviolet light detection (UV, <400 nm), Si for visible–near-infra (NIR, 400–1100 nm), InGaAs for NIR–mid-IR (MIR, 1–5 μm), and HgCdTe for MIR–far-IR detection (FIR, >5 μm) [2]. However, the ultra-miniaturization and integration of photodetectors with multi-materials are challenging, which require complex nanomanufacturing process and exorbitant production costs. In addition, there are some inherent disadvantages. For example, poor flexibility is a common problem in these conventional semiconductor materials, which restricts their application potential in flexible and wearable electronics. Some specific materials (*e.g.,* HgCdTe) are environment toxic and cannot operated at room temperature [1]. The development trend for high-performance detection and different application scenarios prompts scientists to continue to pursue new materials with novel physical properties.

Two-dimensional (2D) materials have attracted tremendous attention in the past few decades [6–12]. Among them, 2D Transition-Metal Dichalcogenides (TMDs) are considered to be promising for next-generation optoelectronics due to the strong light-matter interaction, weak interlayer van der Waals (vdW) interaction, flexible characteristics and the ease of integration with current silicon-based optical electronics [13–17]. Group-10 noble TMDs (NTMDs) are outstanding representatives in the TMDs family [18–20]. The reintroduced new materials are generalized formulated by Group-10 noble elements (Pt, Pd, and so on*.*) and chalcogens (S, Se, or Te). Unlike traditional TMDs, the d-electrons in NTMDs are fully occupied their d-orbitals resulting in the highly hybridized Pz orbits and strong interlayer interactions [21, 22]. Therefore, NTMDs exhibit relatively small and widely tunable bandgaps compared with traditional TMDs (such as MoS2 and WS2). For example, PtS2 shows a layer-dependent bandgap from 1.6 to 0.25 eV [21], while PtSe2 changes from a typical semiconductor state (1.2 eV in 1 L PtSe2) to semi-metal state when the thickness increases to over 5 layers [23]. Combining with the high mobility (>1000 cm2 V−1S−1, larger than most other TMDs and comparable for that of BP) and environmental stability, NTMDs has great potential in photodetectors applications [21, 23–25]. Moreover, the unique puckered pentagonal structure of PdS2 and PdSe2 inherently provides them with anisotropic properties [26–28] and may promote the development of polarized photodetectors.

In this chapter, we first discuss the structural, electronic and optical properties of NTMDs. Then we focus on the NTMDs based photodetectors. Waferscale NTMDs films with high-quality and large-scale monocrystalline NTMDs nanosheets have been fabricated, which are appropriate for optoelectronic applications. NTMDs and their heterostructure based photodetectors show many advantages such as high-performance, ultrawide spectra detection, long-term environment stability, and anisotropic characteristics. NTMDs have great potential for large-scale imaging and flexible devices, which could be the next-generation optoelectronic core materials.
