Study Of Metal Halide Perovskite Based On A Site Regulation And Carbon-Based Perovskite Solar Cells

Recently,researches on metal halide perovskite solar cells?PSCs?have experienced a rapid development.The power conversion efficiency?PCE?of PSCs is up to 25%currently,and it could only reach 3.8%a decade ago,which benefits from the excellent properties of perovskite,such as high absorption coefficient,ultra-long carrier diffusion length,high crystal flaw tolerance,etc.However,stability issues of PSCs puzzle researchers all along,and hinder its commercialization.In this work,mixed-cation lead mixed-halide perovskite containing Cs⁺was employed as light-harvesting layer of PSCs.Meanwhile,a novel architecture of stacking carbon-based PSCs?C-PSCs?was fabricated.The stacking C-PSC composes a photo-anode and a back-electrode,and then two semi-cells are stacked together by a clamp.It can be easily disassembled,replaced and reused,which is especially suitable to cosmically industry production.The stacking graphene electrode is formed by low-cost and facile spray approach,instead of vacuum evaporation method,which is usually used to deposit Au electrode layer.The results are shown as follow:?1?The A site cation of mixed-cation lead mixed-halide perovskite was regulated by adding cesium dopant,which can improve crystallinity and stability of the perovskite film.Our results show that Cs⁺can completely fit into crystalline structure without introducing impurities.It also enhances preferential growth of perovskite with?001?orientation.A blueshift of E_g from1.60 eV to 1.61 eV is observed,and peak position of steady-state PL spectra moves from 784nm to 771 nm correspondingly.Based on our research,light irradiation is the main constraint to stability issues,and adding cesium dopant can improve the photochemical stability of perovskite.?2?Stacking C-PSCs were fabricated with metal halide perovskite containing Cs⁺(Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃),and the electrical properties and microscopic mechanism were carefully investigated.Technique-mature and high-efficiency Au-PSCs were fabricated and measured as the reference.Electrochemical impedance spectroscopy?EIS?and J-V curves are measured and precise models are built to analyze the photogeneration and carrier transport properties of C-PSCs.J-V plot fitting shows lower ideal factor and dark saturate current density for C-PSCs,which indicates fine interfacial contact and less nonradiative recombination centers.However,due to the sparse contact of two detached semi-cells connected by graphene,the series resistance of C-PSCs is higher than that of Au-PSCs.Moreover,the‘parallel-plate capacitor'like stacking electrode architecture impacts a lot in EIS curves,leading to a small arc in low frequency region.Then aging test was carried out for two kinds of PSCs in dark condition under high temperature.Results show that stability of C-PSCs does not have much advantages over Au-PSCs,due to the sophisticated fabricating process of Au electrode.On the one hand,the open circuit voltage of Au-PSCs drops a lot and results in efficiency decline,compared with C-PSCs.It might relate to diffusion of the Au at elevated temperature,which influences internal structures of PSCs.On the other hand,the short circuit current of C-PSCs drops and leads to efficiency decrease.Hypothesis could be proposed that graphene nanoribbons connecting two semi-cells move,shrink or shear off due to internal or external stress during the aging test,leading to microcosmic disconnect of the light-anode and the back-electrode.