Study On Regulation Of Perovskite Crystal Growth And Its Highly Efficient Solar Cell

Organic-inorganic hybrid perovskite materials have been employed as active layer for solar cells（PSCs）application due to their unique photoelectric properties including high electron and hole mobility,long carrier diffusion distance,and wide spectral absorption range.Currently,the highest certified power conversion efficiency（PCE）has reached 25.2%.However,the intrinsic instability of perovskite film restricts the further development of PSCs,and this is closely associated with the crystallization process and morphology of perovskite crystal,which affects the photoelectric properties of the devices such as charge separation and extraction efficiency,carrier recombination and mobility.Improving the crystallinity and grain size,and reducing the grain boundaries have become one of the effective ways to achieve high efficiency and stable PSCs.In this thesis,CsMAFA-based perovskite films are prepared by a one-step rapid crystallization method.The above films are applied to solar cells with the structure of FTO/compact TiO₂/mesoporous TiO₂/perovskite/Spiro-OMe TAD/Au.The influence of precursor concentration on morphologies of mesoporous TiO₂ was studied.The mesoporous TiO₂ layer without nanoparticle agglomeration was prepared.The effect of the concentration of perovskite precursor solution and the drop time of anti-solvent on the morphology,photophysical properties of perovskite films and the performance of solar cells were investigated.The optimal preparation conditions of perovskite solar cell are determined by exploring the above factors.PEAI is synthesized and used as perovskite interface modification molecule to passivate the surface defects of perovskite thin films.Optimized solar cell has achieved a photoelectric conversion efficiency（PCE）of 20.11%.Phenylacetonitrile（PA）and 2-naphthylacetonitrile（2-NA）served as crystal growth regulators are introduced into the perovskite precursor.The coordination effect of n-andπ-electron in regulator molecule with Pb²⁺on the nucleation and growth of FA_0.80MA_0.15Cs_0.05Pb(I_0.85Br_0.15)₃ perovskite crystal,along with passivation of surface defects and grain boundaries are investigated.The interaction between the regulators and Pb²⁺in precursor and its effect on the size and morphology of perovskite crystal are systematically studied by FTIR,XRD,and SEM.The results suggest that n-electron of N atom of nitrile group in PA and 2-NA could form a coordination bond with Pb²⁺,andπ-electron in aromatic ring could also generate a cation-πinteraction with Pb²⁺.This combined effect efficiently delays the crystallization rate of perovskite crystal,and then promotes the growth of grains and reduces the grain boundaries,which enlarges the grain size to 700 nm maximally.UV-Vis,PL and TRPL spectra are characterized to confirm that the prepared perovskite film is favorable for the separation and transformation of more excitons to carriers.The solar cells based on PA-optimized high-crystallinity perovskite film as active layer show a maximum PCE of 21.10%,with an unencapsulated device retaining 91.2%of its initial efficiency for 60 days in 40±5%relative humidity under dark condition,suggesting that the device possesses excellent stability.