Applications Of Surface Plasmon Resonance In Metal Nanoparticles/Transparent Polyimide Composite Film

The noble metals such as gold and silver had never left people's visual field due to their unique stability and beautiful color throughout history.With the increased understanding and control of the atomic world,we can discover many completely different and intriguing phenomena when they are fashioned into structures with nanometer-sized dimensions.For example,the local surface plasmon resonances?LSPR?which is the collective oscillations of free electrons localized at surfaces of nanoparticles made of metals,allows the strengthening of light trapping by increasing the absorption and scattering of incident light.The scattering effect,near-field enhancement and energy transfer effect induced by LSPR exhibit extensive use in solar cells,surface-enhanced Raman and fluorescence spectroscopy.Generally,LSPR was prepared by transferring the dispersion of particles with different shapes and sizes into the corresponding functional layer or solid substrate such as glass,quartz or silicon wafers.As the development of science and technology,the demand on wearable and transparent equipment covering all domains for comfortable material life is growing with time.Therefore,the flexibility of photovoltaic devices and surface enhanced spectroscopy substrates should be a developing trend.However,there still exists some challenges to integrate the LSPR in nanoparticles with the flexible substrate effectively.If only coated the dispersion of nanoparticles onto the flexible substrates,the particles?stability and reproducibility cannot be maintained due to the weak adhesion between particles and substrates.While nanoparticles formed film together with the substrate precursor solution and then dispersed inside substrate,the mechanical stability could be effectively enhanced.Nevertheless,the LSPR cannot be effectively utilized due to the distance dependence when the nanoparticles did not fully expose to the surface.Meanwhile,both the methods mentioned above are inevitably plagued by dispersion of nanoparticle.Herein,suitable and transparent flexible substrates are sought to grow nanoparticles on the surface in situ with available enhanced adhesion,thus avoiding the dispersion of nanoparticles in the meantime.Consequently,the applications of surface-confined nanoparticles composite films in solar cells and surface-enhanced spectroscopy are investigated and the detail work as follows:1)In situ growth of metal nanoparticles on transparent polyimide films.Surface-cleaved imide ring in the chain of polyimide?PI?surface by aqueous alkali,then ion exchange loading metallic silver ion?Ag⁺?,subsequently,using the chemical reduction process successed in growth of Ag nanoparticles on the surface of PI.As a result,this preparation of Ag nanoparticles fully exposed on the surface and possessing a strong adhesion with PI film.Controlling the amount of Ag⁺and the reduction rate,the interparticle distance,diameter and distribution of Ag particles could be effectively modified.This method successfully avoids the problems of dispersion and instability of nanoparticles and thus possessing great advantages in practical applications.This nanoparticle composite PI film provides a flexible substrate candicate for the photovoltaic cells,surface-enhanced Raman and fluorescence spectroscopy.2)Theoretical calculation of the influence factors of the LSPR in nanoparticles.The field intensity distributions of the metal nanostructures were simulated using the finite difference time domain?FDTD?method.For different metal materials?Ag or Au?,LSPR exhibits obvious wavelength selectivity.In addition,the electric field intensity in the LSPR enhanced with the decrease of interparticle distance and the increase of surrounding particles number.And the electric field of hollow structure is more obvious than solid sphere.In consideration of geometrical shape nanostructures,the electric field intensity at the edges and corners is extremely strong because of the lightning rod effect.These simulated results could contribute to further understand the principle of LSPR field enhancement,and provide an important theoretical reference for the efficient utilization of the LSPR effect.3)Application of Ag nanoparticles composite transparent PI film in flexible perovskite solar cells.Based on the above work,the Ag nanoparticles composited PI film with optimized size and interparticle distance was prepared.Thanks to the firmly adhesion between the PI and Ag nanoparticles,flexible perovskite solar cell devices can conveniently fabricate on the composite PI substrate.With the help of LSPR effect in Ag nanoparticle composite PI film,the efficiency of light harvesting and exciton separation and extraction in the perovskite absorber are effectively enhanced,thus improving the short-circuit current(J_sc)of the device.Moreover,the introduction of Ag nanoparticles altered the wettability of PI surface and successfully reduced the sheet resistance of the flexible electrode.Consequently,the J_sc in flexible perovskite solar cell based on CH₃NH₃PbI₃ absorber is improved by 60%and the power conversion efficiency?PCE?is increased from 5.41%to 10.41%compared to the bare PI device.The Ag nanoparticles composite transparent PI film provides a promising candicate for the flexible substrate in wearable perovskite solar cells.4)Utilization of patterned Ag nanoparticles composite transparent PI film as flexible substrate in surface-enhanced fluorescence spectroscopy.Combine with the chemical reduction and the photolithography technology,the surface-adhered grid patterned Ag nanoparticles were successfully prepared on the transparent PI film,and then applied as a flexible platform for the surface metal enhanced fluorescence spectroscopy?SEF?.Controlling the size of particles in the grid can effectively modified the SEF efficiency.Meanwhile,the effect of the distance between fluorophore and metal structure on SEF intensity was also investigated.It was found that the introducing a10-nm PEI interlayer could achieve the optimal SEF efficiency?4.5 folds?.Furthermore,because of the robust adhesion between the particles and the flexible substrate,the stable and efficient SEF performance was maintained after 1000 cyclic bending.Those result provides a new method for the preparation of flexible SEF substrates for clinical analysis and life sensing in the future.5)Incorporation Ag@Au core-shell nanoparticle composite PI film in surface-enhanced Raman and near-infrared fluorescence spectroscopy.On the basis of the above work,Ag@Au core-shell nanoparticles were grown in situ on PI and applied as a flexible substrate to surface-enhanced Raman?SERS?and near-infrared fluorescence spectroscopy.As a result,without additional surface pretreatment,a 356 times enhanced Raman signal were acquired with the target single molecule adsorbed on the surface of flexible SERS platform.In addition,the Raman peak can be clearly observed when concentration of the target molecule down to 10^-8 M indicating that highly sensitive detection capability of the flexible SERS platform.Due to the advantages of in situ growth of the core-shell nanoparticle,the Raman intensity on the flexible SERS paltform was still stable without any degradation after mechanical stimuli?bending or torsion?1000 cycles.Moreover,Ag@Au core-shell nanoparticles make their LSPR region broder and overlap larger with the excitation and fluorescence spectra of visible dye molecules.Thus,applying them as a flexible SEF platform can obtain a 12 folds of fluorescence enhanced.Furthermore,with the increase thickness of Au shell layer,the LSPR region gradually shifted to the near-infrared region,consequently,a 4.4 times fluorescence enhancement were found in the near-infrared fluorophore.It can be seen that Ag@Au nanoparticles composite PI films possessing great potential in future application of the flexible SERS and SEF platform.