Research On Surface Plasmon-enhanced Inverted Perovskite Solar Cells

Since the first report on perovskite solar cells?PSCs?with an efficiency of 3.8%in 2009,a great deal of effort has been made to improve the device performance.Over the past few years,PSCs have realized power conversion efficiency?PCE?of exceeded 24.2%through optimizing material and device structures.Perovskite material is an ideal light absorber for the high-efficiency solar cells due to their suitable bandgap,high absorption coefficient,ambipolar carrier transport property and long electron/hole diffusion length of more than 1?m.Among various organometal halide perovskite materials,CH₃NH₃PbI₃ has achieved much attention due to its suitable bandgap of about 1.55 eV,large absorption coefficient of 10⁵ cm^-1 and simplified stoichiometry.In general,most state-of-the-art CH₃NH₃PbI₃ based planar heterojunction PSCs without any pre-or post-treatment show PCEs of about 15%.Many approaches have been employed to enhance the PCEs of these devices,including the solvent engineering,vapor-assisted solution deposition,hot-substrate casting,and a number of post-treatments including anti-solvent rinsing treatment and thermal or solvent annealing.On the other hand,noble metal nanostructure-induced surface plasmons are considered as another useful method to further improve the PCEs of PSCs.In this thesis,Au nanorods were synthesized and disposed on the PEDOT:PSS hole transfer layer?HTL?of inverted planar PSCs.The influence of surface plasmon resonance?SPR?effect of Au nanorods on device performance as well as the inner mechanism was investigated.At first,the effect of nanoparticles'concentrations on device performance was studied and an optimized Au nanorods concentration of 6%was verified.The optimized device achieved the best PCE of 15.3%,showing an enhancement factor of 12.83%compared with standard device without Au nanorods disposition.Our study also indicate a negligible influence of Au nanorods addition on the crystallization and formation of the perovskite films.However,the light absorption of perovskite layer was improved when Au nanorods were added due to its wide absorption range,which contribute to the significantly improved device performance.In addtion,in consideration of the direct contact between perovskites and the bare Au nanorods will inevitably leads to serious exciton quenching and free carriers recombination,a² nm ultrathin PSS shell is covered onto the Au nanorods to form a Au@PSS nanorods core-shell structure.The Au@PSS nanorods was added into the PSCs with the same device structure as before and the effect of Au@PSS nanorods was further studied.The best PCE of 15.89%was achieved by the device with Au@PSS nanorods addition,showing an enhancement factor of 17.2%compared with standard device and 3.9%compared with that of PSC doped with bare Au nanorods.These results indicate a benefiting from PSS shell can effectively suppress the electron and hole recombination caused by its surface,accelerate excitons ionization,and thus leading to an improved device performance.Secondly,Ag@SiO₂ nanocubes?NCs?were further introduced into PSCs between the interface of CH₃NH₃PbI₃ and HTL and the effect of nanoparticles'concentrations on device performance was analyzed.The optimum concentration of Ag@SiO₂ NCs in PSCs is 3 vol%and the optimized device achieved the best PCE of 17.22%and the highest short circuit current density of 22.58 mA/cm²,showing an enhancement factor of 18.1%and 11.7%compared with standard device,respectively.The local electric field of Ag@SiO₂ NCs was simulated with a finite differential time domain?FDTD?method,and the results showed that Ag nanocubes with sharp corners can induce more intense EM fields in the range of about 460 nm,which is helpful to enhance light absorption of the active layer in this high energy region.Thus,the improved photoelectric conversion efficiency of CH₃NH₃PbI₃based PSCs in this region was realized.In general,a low conversion efficiency in this short-wavelength region was measured for CH₃NH₃PbI₃ based PSCs without Ag@SiO₂ NCs addition.Moreover,the lower charge transfer resistance studied by the electrochemical impedance spectroscopy?EIS?,together with the reduced intensities and lifetime of perovskite/HTL interface tested by steady-state and time-resolved transient photoluminescence?PL?spectra characterizations demonstrates more efficient exciton dissociation and charge transfer in the PSCs with Ag@SiO₂ NCs addition.