We demonstrate a low-repetition-rate all-fiber allnormal-dispersion Yb-doped mode-locked fiber laser. Stable mode-locking is achieved by nonlinear polarization rotation and its spectral-filtering effect. Nanosecond pulses with steep edges spectrum at repetition rate 217.4 kHz are achieved. Our preliminary experiment shows that it is a promising seed for all-fiber amplifier system.

By using the symmetry properties of the reversible planar maps, instead of the Melnikov analysis, we improve the homoclinic orbit approach without assuming small perturbations to prove rigorously the existence of bright and dark soliton solutions of the discrete nonlinear Schrödinger equations with various nonlinearities in one-dimensional lattices. Our approach is valid both for small and large coupling constants. The latter case is inaccessible to the anti-integrability method.

No abstract

No abstract

Lithium-sulfur (Li-S) batteries are competitive for the next-generation energy storage applications. However, soluble polysulfides cause severe shuttle effect and electrolyte abuse. Solid-solid and quasi-solid conversions are effective to address the...

Formamidinium lead triiodide (FAPbI3) perovskite has attracted intensive research attention due to its ideal band gap and low defect density for photovoltaic applications. Particularly, the existence of non-photoactive δ-phase FAPbI3 has been considered detrimental to regular-structured perovskite solar cells (PSCs). Here, in hole-conductor-free triple-mesoscopic PSCs, we observe that α-phase FAPbI3 transforms to δ-phase FAPbI3 at the perovskite/carbon interface and in situ forms an α/δ-phase junction when the as-fabricated cells are exposed to humid atmosphere. The α/δ-phase junction shows a favorable band alignment and significantly suppresses the charge recombination at the interface. By controlling the relative humidity of the atmosphere, we fabricate FAPbI3-based cells that deliver a champion efficiency of 17.11% with an enhanced open-circuit voltage (V OC) of 1020 mV. This work demonstrates the potential of δ-phase FAPbI3 for benefiting the device performance of PSCs and proposes the concept of constructing perovskite-based junctions at the interface between a perovskite-absorbing layer and charge-transporting layers for enhancing the V OC of PSCs.

No abstract

Perovskite solar cells (PSCs) have achieved high efficiencies with diversified device architectures. In particular, printable mesoscopic PSC has attracted intensive research attention due to its simple fabrication process and superior stability. However, in the absence of hole conductors, the unfavorable energy band alignment between the perovskite and the carbon electrode usually leads to the reduction of device performance, especially the open-circuit voltage (V OC ). Here, a p-type molecule, 2,3,5,6tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), is utilized to post-treat the perovskite/carbon interface, which benefits the charge transfer and suppresses the charge recombination within the device. As a result, the post-treated device delivers a power conversion efficiency of 18.05% with an enhanced V OC of 1044 mV. This work provides a facile method for tuning the interfacial energy band alignment and improving performance of printable mesoscopic PSCs.