Jun Xi

Highly Transparent, Conductive, Flexible Resin Films Embedded with Silver Nanowires

In this article, a low sheet resistance and highly transparent silver nanowire (AgNW) resin composite film was demonstrated, which was prepared by a simple and efficacious two-step spin-coating method. By burying the AgNWs below the surface of the transparent resin matrix which was cured at 150 °C in air, we achieved a uniform, highly transparent, conductive, flexible film. Compared to the reported transparent electrodes, this composite transparent and conductive film showed 10 Ω/□ sheet resistance and nearly 90% mean optical transmittance over the UV-visible range simultaneously. Undergoing hundreds of cycles of tensile and compression folding, the composite film slightly increased its sheet resistance by less than 5%, displaying good electromechanical flexibility. These characteristics of the composite AgNW-resin films were expected to be used in applications of flexible optoelectronics.

Construction of Compact Methylammonium Bismuth Iodide Film Promoting Lead-Free Inverted Planar Heterojunction Organohalide Solar Cells with Open-Circuit Voltage over 0.8 V

A bismuth-based organohalide material, methylammonium bismuth iodide (MA3Bi2I9), has been recently explored as an efficient lead-free light absorber in photovoltaic applications. However, the poor surface morphology of the MA3Bi2I9 film fabricated via conventional one-step spin-coating methods has limited the performance of the device. In this work, a smooth, uniform, and compact MA3Bi2I9 thin film was realized by a novel two-step evaporation-spin-coating film fabrication strategy for the first time. Taking advantage of the superior MA3Bi2I9 thin film, the best-performing inverted planar heterojuncion photovoltaic device exhibited a power conversion efficiency of 0.39% with open-circuit voltage as high as 0.83 V, which demonstrated the lowest loss-in-potential to date in MA3Bi2I9-based solar cells. Moreover, the facile film fabrication strategy utilized in this work paves the way for high reproducibility of lead-free organohalide films and devices.

Ag-encapsulated Au plasmonic nanorods for enhanced dye-sensitized solar cell performance

In this article, Ag-encapsulated Au nanorods (Au@Ag NRs) are prepared and introduced into dye-sensitized solar cells (DSSCs). As a unique plasmonic nanostructure, this composite exhibits the superiorities of enhanced light-harvesting as well as restrained charge recombination of DSSCs. Remarkably, the enhanced light absorption of the photoanode can be obtained via the surface plasmon resonance (SPR) effect of the Au@Ag NRs, whereas a broadened absorption in the red and near-infrared (NIR) region ensures the full utilization of the solar energy. Beyond the dominated optical utility, the presence of the Au@Ag NRs promotes the suppression of the charge recombination, further enhancing the photochemical catalysis of DSSCs. An optimized Au@Ag NR modified DSSC is achieved with a power conversion efficiency of 8.43%, which is significantly superior to that of the pure TiO2 DSSC with a PCE of 5.91%.

Formation of ultrasmooth perovskite films toward highly efficient inverted planar heterojunction solar cells by micro-flowing anti-solvent deposition in air

Ultrasmooth perovskite thin films are prepared by a solution-based one-step micro-flowing anti-solvent deposition (MAD) method carried out in air with simplicity and practicability. Engaging inert gas blow and anti-solvent drips as accelerators, ultrafast crystallizing, thickness controllable, and high quality methylammonium lead iodide films are prepared with a least root mean square roughness of 1.43 nm (1.95 nm on average), achieving the smoothest surface morphology to the best of our knowledge, as well as a rather compact perovskite layer with a high coverage ratio. Perovskite films formed from MAD require no annealing procedure to ultimately crystallize, realizing a very fast crystallizing procedure within few seconds. By controlling the thickness of perovskite films, superior photovoltaic performance of solar cells with a large fill factor of 0.8 and a PCE of 15.98% is achieved without a glovebox. MAD technology will benefit not only highly efficient photovoltaic devices, but also perovskite-based hybrid optoelectronic devices with field effect transistors and light emitting diodes as well.

Enhanced lasing assisted by the Ag-encapsulated Au plasmonic nanorods.

Threshold reduction and emission enhancement were reported for the waveguided random lasing, assisted by the Ag-encapsulated Au nanorods (Au@Ag NRs). The blend of tris(8-hydroxyquinolinato)aluminum (Alq3) and 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4 H-pyran (DCJTB), which comprise the typical donor-acceptor lasing system, is used as the gain media. Compared with the Ag nanoparticles and Au nanorods, Au@Ag NRs exhibited the broad absorption spectra of localized surface plasmon resonance (LSPR) with multiple peaks, which sufficiently overlapped with both absorption and emission spectra of the donor-acceptor system of the gain media. This unique plasmonic characteristic of Au@Ag NRs leads to the lower lasing threshold and enhances the lasing efficiency by the effects of both enhancement of localized electromagnetic field and scattering.

Electric field-modulated amplified spontaneous emission in organo-lead halide perovskite CH3NH3PbI3

The electric field-modulation of the spontaneous emission (SE) and amplified spontaneous emission (ASE) in organo-lead halide perovskite CH3NH3PbI3 (aliased as MAPbI3) layer has been investigated. With the increase of the external applied electric field, the electric field-induced quenching of the SE and ASE intensity was observed, accompanying with a blue-shift of the ASE emission peaks, which can be attributed to field-induced ionization of photogenerated excitons in the MAPbI3 layer. Based on the analysis of quenching factor and the dielectric constant, we estimated an exciton binding energy ∼36 meV at room temperature, which will provide useful insights into the optical-electrical characteristics of MAPbI3 and pave the way for the future optoelectronic applications.

High-Quality Cs2AgBiBr6 Double Perovskite Film for Lead-Free Inverted Planar Heterojunction Solar Cells with 2.2 % Efficiency

All-inorganic double-metal perovskite materials have recently gained much attention due to their three dimensionality (3D) and non-toxic nature to replace lead-based perovskite materials. Among all those double perovskite materials, theoretical works have demonstrated that Cs2 AgBiBr6 shows high stability and possesses a suitable band gap for solar-cell applications. However, the film-forming ability of Cs2 AgBiBr6 is found to be the utmost challenge hindering its development in thin-film solar-cell devices. In this work, a high-quality Cs2 AgBiBr6 film with ultra-smooth morphology, micro-sized grains, and high crystallinity is realized via anti-solvent dropping technology and post-annealing at high temperature. After optimization, the first example of an inverted planar heterojunction solar-cell device based on Cs2 AgBiBr6 exhibits a power conversion efficiency of 2.23 % with VOC =1.01 V, JSC =3.19 mA/cm2 , and FF=69.2 %. Besides, the device shows no hysteresis and a high stability.

Rubidium Doping for Enhanced Performance of Highly Efficient Formamidinium-Based Perovskite Light-Emitting Diodes

Organometal halide perovskites (OHPs) have become the most promising optoelectronic material in the past few years with a myriad of applications in the photovoltaic, light-emitting, and laser fields. However, for light-emitting applications, the low photoluminescence quantum yield (PLQY) of OHP film is critical to hinder the efficiency improvement of OHP-film-based light-emitting diodes (PeLEDs). Herein, we study the effects of rubidium incorporation on the crystal growth, structure, and photoelectric and optical properties of formamidinium-lead-bromide-based (FAPbBr3-based) perovskite films and light-emission performance of PeLEDs. It is found that rubidium incorporation can significantly enhance the PLQY of FAPbBr3 film by suppressing the trap density and thus improve the withstand voltage as well as the performance of PeLEDs. When FAPbBr3 film with optimal Rb doping ratio is employed as the light emitter of PeLEDs, the maximum luminance and current efficiency is enhanced by ∼10-fold and ∼5-fold to 66 353 cd/m2 and 24.22 cd/A compared to the controlled device, respectively, the record performance based on FAPbBr3 PeLEDs so far. The enhanced performance can be chiefly attributed to the increase of PLQY and decrease of trap defect density of perovskite film with rubidium incorporation. Our research is expected to stimulate the development of OHPs for the next-generation lighting and display fields.