Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer topological insulator (TI) is, to the best of our knowledge, experimentally demonstrated for the first time. The few-layer TI: Bi 2 Se 3 (2-4 layer thickness) is fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm 2 measured by the Z-scan technique. The optical deposition technique is used to induce the few-layer TI in the solution onto a fiber ferrule for successfully constructing the fiber-integrated TI-based saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable Q-switching operation at 1.06 μm is achieved. The Q-switched pulses have the shortest pulse duration of 1.95 μs, the maximum pulse energy of 17.9 nJ and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate that the TI as a SA is also available at 1 μm waveband, revealing its potential as another wavelength-independent SA (like graphene).

To engineer the NiO x /perovskite interface and promote interfacial hole transfer, two pyridine-terminated conjugated small organic molecules (PTZ-1 and PTZ-2) are synthesized to link the NiO x and perovskite layers for NiO x -based perovskite solar cells (PSCs). One terminal pyridine group interacts with the NiO x layer, while the other one coordinates with the Pb atoms of the perovskite layer, erecting an interfacial hole transfer bridge between NiO x and perovskite. Surface modification of the NiO x film with the PTZ molecules is able to enhance hole extraction, increase hole mobility and conductivity of NiO x , reduce defect density, and retard interfacial charge recombination. As a consequence, power conversion efficiency is improved from 12.53 to 16.25 and 17.00% upon surface modifications of NiO x with PTZ-1 and PTZ-2, respectively. Furthermore, the modified PSCs exhibit almost no hysteresis and show good stability after storage in air (relative humidity of 30–40%) for 500 h without encapsulation.

V1−xWxO2(M/R) nanorods with superior doping efficiency (103 °C per at% W) and thermochromic property (Tvis = 60.6%, ΔTsol = 10.3%) were synthesized using a one-step hydrothermal method.