Yuzong Gu

Large third-order optical nonlinearity in SrBi2Ta2O9 thin films by pulsed laser deposition

Well-crystallized SrBi2Ta2O9 (SBT) thin films with good surface morphology were prepared on quartz substrates by the pulsed laser deposition technique at a deposition temperature of 750 °C. The third-order nonlinear optical properties of the films were measured by the Z-scan technique. The magnitude and sign of the nonlinear refractive index n2 were determined, as was the negative sign, which indicated a self-defocusing optical nonlinearity. A nonlinear refractive index as high as 1.9×10−6 esu was displayed in the SBT thin film. These results show that SBT ferroelectric thin films have potential applications in nonlinear optics.

Local structure and magnetic properties of Mn-doped 3C-SiC nanoparticles

Mn-doped 3C-SiC nanoparticles have been fabricated by a sol-gel and carbothermal reduction method. The average particle size of the nanoparticles is about 126 nm. Raman scattering studies indicate that the transverse optical and the longitudinal optical modes shift to low wave number and the full widths at half-maximum of Raman peaks increase after Mn was doped. Extended x-ray absorption fine structure reveals that the doped-Mn atoms substitute for the C sites in the 3C-SiC lattice. Magnetic measurement results show that the room temperature intrinsic ferromagnetism (FM) order is established. The origin of the FM has been discussed in detail.

Aspect ratio-related three-photon absorption and mechanism of α-FeOOH nanorods in the near-infrared.

Tuning a semiconductor nanomaterial with large three-photon absorption (3PA) cross section in the near infrared and investigating the relationship between the nanostructure and nonlinear optical properties is a challenging topic, which is of significance in potential applications. Here, we report the aspect ratio-related 3PA response of α-FeOOH nanorods (NRs) in the near infrared. Large 3PA cross section at room temperature is achieved as high as ~10(-77) cm(6) s(2) photon(-2) when the distribution of photo-induced and intrinsic surface polarization charges of excitons to both ends of NRs is tuned through the aspect ratio, yielding total enhancement more than three times larger than that of NRs with 12.1 nm diameter.

Nonlinear optical enhancement induced by synergistic effect of graphene nanosheets and CdS nanocrystals

CdS nanocrystals are attached on graphene nanosheets and their nonlinear optical properties are investigated by picosecond Z-scan technique at 532 nm. We found that synergistic effect between the graphene and CdS makes a major enhancement on the nonlinear optical absorption of graphene/CdS nanohybrid in comparison with cooperative effect, and the synergistic improvement is restricted by nonradiative defects in hybrid. The synergistic mechanism involving the local field theory and charge transfer evolution is proposed.

Insights into collaborative separation process of photogenerated charges and superior performance of solar cells

ZnO nanowires/Cu4Bi4S9 (ZnO/CBS) and ZnO nanowires/CBS-graphene nanoplates (ZnO/CBS-GNs), as well as two types of solar cells were prepared. The photovoltaic responses of CBS-GNs and ZnO/CBS-GNs can be improved with incorporation of GNs. The transient surface photovoltage (TPV) can provide detailed information on the separation and transport of photogenerated carriers. The multichannel separation process from the TPVs indicates that the macro-photoelectric signals can be attributed to the photogenerated charges separated at the interface of CBS/GNs, rather than CBS/ZnO. The multi-interfacial recombination is the major carrier loss, and the hole selective p-V2O5 can efficiently accelerate the charge extraction to the external circuit. The ZnO/CBS-GNs cell exhibits the superior performance, and the highest efficiency is 10.9%. With the adequate interfaces of CBS/GNs, GNs conductive network, energy level matching, etc., the excitons can easily diffuse to the interface of CBS/GNs, and the separated electrons and holes can be collected quickly, inducing the high photoelectric properties. Here, a facile strategy for solid state solar cells with superior performance presents a potential application.

Comprehensive Insights into Charge Dynamics and Improved Photoelectric Properties of Well-Designed Solar Cells

Here, Zn2SnO4 nanorods/Cu4Bi4S9 (ZTO/CBS) and ZTO nanorods/CBS-graphene nanosheets (ZTO/CBS-GNs), as well as two types of bulk heterojunction (BHJ) solar cells with high flexibility were fabricated on stainless steel meshes (SSMs). The excellent photovoltaic responses of CBS-GNs and ZTO/CBS-GNs with incorporation of GNs were determined using surface photovoltage spectroscopy (SPS). The signals of time-resolved fluorescence response (TFR) and transient surface photovoltage (TPV) can provide more detailed information for transition, separation, and transport of photoinduced carriers. Besides, the ZTO nanorods/CBS-GNs cell exhibits the superior performance and the highest efficiency is 11.2%. The multichannel separation process from the TPVs indicates that the macro-photoelectric signals can be attributed to the photogenerated charges separated at the interface of CBS/GNs, rather than CBS/ZTO. The multi-interfacial recombination is the major carrier loss with electrical impedance spectroscopy (EIS) and the hole selective NiO can efficiently accelerate the charge extraction to the external circuit. The comprehensive signals of SPS, EIS, TFR, and TPV provide insights into transition, separation, recombination and shifting of carriers. Importantly, the BHJ flexible solar cells with high efficiency and facile, scalable production present a potential for application.

Photochemical charges separation and photoelectric properties of flexible solar cells with two types of heterostructures

Photochemical charges generation, separation, and transport at nanocrystal interfaces are central to energy conversion for solar cells. Here, Zn2SnO4 nanowires/Cu4Bi4S9 (ZTO/CBS), ZTO nanowires/CBS-reduced graphene oxide (ZTO/CBS-RGO), and bulk heterojunction (BHJ) solar cells were measured. The signals of steady state and electric field-induced surface photovoltage indicate that RGO with high electron mobility can evidently improve the photovoltaic response. Besides, ZTO/CBS and ZTO/CBS-RGO cells exhibit the excellent performance and the highest efficiencies of 1.2% and 2.8%, respectively. The internal relations of photoelectric properties to some factors, such as film thickness, direct paths, RGO conductive network, energy level matching, etc., were discussed in detail. Qualitative and quantitative analyses further verified the comprehensive effect of RGO and other factors. Importantly, the fine bendable characteristic of BHJ solar cells with excellent efficiency and facile, scalable production gives the as-made flexible solar cells device potential for practical application in future.

Surface-related nonlinear optical enhancement in graphene and G/CdS nanohybrids

In the past few years, significant progress has been made in the structure design, growth and nonlinear optical properties of graphene and graphene-based nanohybrids. The surface defects on the nanomaterials play an important role on the optical nonlinearity of graphene and graphene-based nanohybrids owing to a large surface-to-volume ratio in the nanomaterials. To investigate the correlation between surface defects and the synergistic nonlinear optical response in graphene-based nanocomposites, we attached CdS nanocrystals on the surface of graphene and prepared G/CdS nanohybrids and graphene nanosheets consisting of different oxygen-containing functional groups via chemical method, which are determined by experimental measurements of FTIR and XPS characterization. The nonlinear optical absorption and refraction of G/CdS nanohybrids under single pulse laser irradiation are enhanced 10.8 times with the concentration decrease of surface oxygen-containing groups, which might be attributed to the local field effects and synergetic effects stemming from charge transfer between the two components. Surface oxygen-containing defects tuned nonlinear optical absorption and refraction of graphene nanosheets are also investigated. Tuning the surface oxygencontaining defects of graphene and G/CdS nanohybrids is a useful way to enhance the optical nonlinearity for potential applications in devices.

Synthesis and enhanced third-order nonlinear optical effect of ZnSe/graphene composites

ZnSe/graphene composites are produced by chemical method, and the attachment of ZnSe nanocrystals on graphene nanosheets can be confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and UV-vis spectroscopy. The nonlinear optical properties are investigated at 532 nm by a picosecond laser Z-scan technique. It is found that the interaction between ZnSe and graphene enhances the optical nonlinearity of ZnSe/graphene composites than single ZnSe or graphene. The increase of ZnSe size further enhances the optical nonlinearity of ZnSe/graphene.

Competition of carrier separation and recombination for an optimized electrode configuration for flexible thin-film solar cells

The inhibition of the rapid recombination of photochemical charges at heterointerfaces and the promotion of transfer and extraction are central to photoelectric conversion in solar cells. With the use of Cu4Bi4S9 nanoribbons-graphene sheets (CBS-GSs) as a hybrid photosensitive layer and the growth of ZnO nanowires on Zn2SnO4 nanowires (ZTO-ZnO) for the electron transfer layer, a flexible solar cell ZTO-ZnO/CBS-GSs was prepared on a stainless steel mesh. In this study, time-resolved fluorescence spectroscopy (TFS) and transient surface photovoltage (TPV) were used to describe the transition and transport process for the photogenerated carriers. With a high fill factor (0.76) and improved electron mobility for the ZTO-ZnO nanostructure, a high photoelectric conversion efficiency of 11.6% was obtained, which was evidently higher than that of a ZTO/CBS-GSs cell (9.2%) and a ZnO nanoparticles/CBS-GSs cell (3.9%). The efficient dissociation of photogenerated carriers at CBS-GSs interfaces, rapid transfer of free electrons in the ZTO-ZnO system, and fast extraction of holes from the selective NiO layer with an optimized architecture led to a superior performance. The charge recombination at the interface can be determined by electrochemical impedance spectroscopy (EIS). Active exploration via inevitable competition between charge separation and recombination (TFS, TPV, EIS, etc.) can provide insights into the entire dynamic process and a separation mechanism for photoinduced carriers, which can also promote the application of flexible thin-film solar cells.