Bulk-like molybdenum disulfide (MoS2) thin films were deposited on the surface of p-type Si substrates using dc magnetron sputtering technique and MoS2/Si p-n junctions were formed. The vibrating modes of E12g and A1g were observed from the Raman spectrum of the MoS2 films. The current density versus voltage (J-V) characteristics of the junction were investigated. A typical J-V rectifying effect with a turn-on voltage of 0.2 V was shown. In different voltage range, the electrical transporting of the junction was dominated by diffusion current and recombination current, respectively. Under the light illumination of 15 mW cm−2, the p-n junction exhibited obvious photovoltaic characteristics with a short-circuit current density of 3.2 mA cm−2 and open-circuit voltage of 0.14 V. The fill factor and energy conversion efficiency were 42.4% and 1.3%, respectively. According to the determination of the Fermi-energy level (∼4.65 eV) and energy-band gap (∼1.45 eV) of the MoS2 films by capacitance-voltage curve and ultraviolet-visible transmission spectra, the mechanisms of the electrical and photovoltaic characteristics were discussed in terms of the energy-band structure of the MoS2/Si p-n junctions. The results hold the promise for the integration of MoS2 thin films with commercially available Si-based electronics in high-efficient photovoltaic devices.

Metal-free borates have emerged as a new class of solid-state chemistry and related crystalline materials with high performance. However, the discovery of metal-free borate crystals that can meet the phase-matching behavior in the short-wavelength ultraviolet (UV) spectral region is extremely limited. Against this background, two new guanidinium fluorooxoborates with the chemical formula of [C­(NH2)3]­[B3O3F2(OH)2] and [C­(NH2)3]2[B3O3F4(OH)] have been discovered and characterized as high-performance candidates for short-wavelength UV nonlinear optical (NLO) applications. The optimally aligned configuration of coplanar [C­(NH2)3] cations and [B3O3F2(OH)2]/[B3O3F4(OH)] heteroanionic units makes both crystals have a sufficiently large NLO coefficient, birefringence, and band gap, which indicate that both metal-free hydroxyfluorooxoborates are promising NLO crystals. The well-ordered configurations of OH/F anions in two borates were identified using various approaches, and the origin of high optical performance was validated by additional measurements and calculations. Our findings verified the feasibility of searching NLO crystals in the short-wavelength region in a metal-free borate system via an eco-friendly and low-cost way.

The development of new infrared (IR) nonlinear optical (NLO) materials with strong second-harmonic generation (SHG) responses and high laser-induced damage thresholds (LIDTs) is urgent but challenging. Herein, the defective diamond-like chalcogenide Hg 3 P 2 S 8 (HPS) was rationally designed and fabricated by a flexible and rigid tetrahedral motif combined strategy. HPS exhibits a phase-matching SHG response of ∼3.6 × AGS (the largest one in the reported ternary sulfides), high LIDT (∼3 × AGS), wide IR transparent region (0.43−16.3 μm), moderate birefringence (0.043 at 1064 nm), and good physicochemical stability and crystal growth habits. Theoretical analyses confirm that the large SHG effect originates from the synergistic effects between distorted HgS 4 , PS 4 , and vacancy-induced nonbonding electrons. The results indicate that HPS is a promising NLO candidate for high-power, high-efficiency laser output in the mid-IR region, which provides an insight into the exploration of new IR NLO materials.

Maximizing the optical anisotropyi nb irefringent materials has emerged as an efficient route for modulating the polarization-dependent light propagation. Currently,t he generation of deep-ultraviolet (deep-UV) polarized light below 200 nm is essential but challenging due to the interdisciplinary significance and insufficiency of high-performing birefringent crystals.H erein, by introducing multiple heteroanionic units, the first sodium difluorodihydroxytriborate-boric acid Na-[B 3 O 3 F 2 (OH) 2 ]•[B(OH) 3 ]h as been characterized as an ovel deep-UV birefringent crystal. Tw or are heteroanionic units, [B 3 O 3 F 2 (OH) 2 ]and [B(OH) 3 ], optimally align to induce large optical anisotropyand also the dangling bonds are eliminated with hydrogens,w hichr esults in an extremely large birefringence and band gap.T he well-ordered OH/F anions in [B 3 O 3 F 2 (OH) 2 ]a nd [B(OH) 3 ]w ere identified and confirmed by various approaches,a nd also the origin of large birefringence was theoretically discussed. These results confirm the feasibility of utilizing hydrogen involved heteroanionic units to design crystals with large birefringence,a nd also expand the alternative system of deep-UV birefringent crystals with new hydroxyfluorooxoborates.