Microstructure Design And Photovoltaic Performance On Inorganic Halide Perovskite Solar Cells

Inorganic metal halide perovskite materials have attracted increased attention due to their tunable bandgap,controllable composition,outstanding photovoltaic performance and stability.However,perovskite solar cells(PSCs)based on inorganic perovskite active layer still face with several key issues.Therefore,investigating the perovskite microstructure,optical properties and carrier transport dynamics,establishing the relationship between device configuration and optoelectronic performance,solving the problems such as phase structure instability,energy level mismatch and carrier recombination loss are crucial for achieving highly efficient and stable inorganic PSCs.In this case,from the two aspects of structure regulation and device optimization,the composition and crystal structure of inorganic perovskites are precisely modulated,and the heterojunction and interface are rationally designed for improving the light absorption ability,charge carrier transport kinetics,as well as the power conversion efficiency(PCE)of inorganic PSCs.In addition,the physical mechanisms between carrier separation,transport,recombination and photovoltaic performance are studied thoroughly.The main research contents contain the following five parts.(1)CI doped CsPbBr3 inorganic perovskite thin films were prepared by solution chemical sequential deposition method.The effects of Cl doping on the morphology,phase structure,photophysical properties and photovoltaic performance of CsPbBr3 inorganic perovskite were systematically studied.The results demonstrate that CI doping increases the tolerance factor of inorganic perovskite material,cause the lattice shrinkage of orthorhombic phase CsPbBr3,and finally lead to the transformation of CsPbBr3 from orthorhombic phase to cubic phase.Compared with the orthorhombic inorganic perovskite CsPbBr3,the cubic inorganic perovskite CsPbBr3 has an increased optical bandgap(from 2.28 eV to 2.32 eV)and an improved carrier lifetime(from 6.7 ns to 14.3 ns).Moreover,the cubic CsPbBr3 PSCs show faster carrier transport efficiency and slower electron carrier recombination rate.The optimized Cl doped cubic CsPbBr3 PSC achieve a short-circuit current density of 8.47 mA cm-2 and a highest PCE of 6.21%,much higher than those of orthorhombic CsPbBr3 PSCs(6.22 mA cm-2 and 3.78%).(2)A novel and simple polyvinylpyrrolidone(PVP)surface passivation strategy was used to prepare room temperature stable cubic CsPbI3 inorganic perovskite films.The surface chemical state of cubic CsPbI3 crystal in the presence of PVP was investigated by FTIR and NMR.The mechanism of stabilizing cubic CsPbI3 was proposed,that is,the chemical bond between acylamino group and CsPbI3 in PVP molecule can increase the surface electron cloud density of CsPbI3,thus reducing the surface tension of perovskite and stabilizing cubic CsPbI3.The cubic CsPbI3 inorganic perovskite prepared by PVP passivation strategy exhibis an ultra-long carrier lifetime(338.7 ns)and carrier diffusion length(more than 1.5?m).The cubic phase CsPbI3 inorganic PSC based on this strategy achieves a highest PCE of 10.74%and excellent thermal/moisture stability.(3)A novel PSC configuration based on MAPbI3-CsPbX3 gradient heterojunction(GHJ)was successfully constructed by precisely adjusting the composition and graded energy level structures of mixed-halide inorganic perovskite CsPbX3 nanocrystals.The GHJ shows a continuous energy band structure arrangement,which can enhance the built-in electric field and increase the depth of depletion layer,thus greatly enhancing the separation efficiency of electron-hole pairs in the perovskite optical absorption layer In addition,the GHJ with a multi-level gradient barrier can reduce the carrier recombination loss at the interface and improve the short-circuit current density and open circuit voltage of PSCs.Compared with the pristine PSCs without hole transport layer,the introduction of inorganic perovskite GHJ enhances the hole transport efficiency from optical absorption layer to electrode,resulting in a decrease of carrier lifetime from 17.54 ns to 7.21 ns.The PSC based on inorganic perovskite GHJ achieves highest PCE of 11.33%,which is nearly 40%higher than the reference PSCs without hole transport layer.(4)Two-dimensional black phosphorus nanoflakes with controllable number of layers were successfully prepared by the liquid phase exfoliation method,and the two-dimensional black phosphorus-perovskite heterojunction was constructed.The effects of two-dimensional black phosphorus on the optical properties,photophysical properties and photovoltaic performance of inorganic perovskite were studied,and the influence mechanisms of two-dimensional black phosphorus on the exciton transport kinetics of perovskite was established.The results show that the introduction of two-dimensional black phosphorus can improve the relative dielectric constant of inorganic perovskite,reduce the exciton binding energy of inorganic perovskite and improve the efficiency of exciton separation,so as to improve the photocurrent output of inorganic PSCs.In addition,the built-in electric field in two-dimensional black phosphorus-perovskite heterojunction can promote the carrier transport efficiency at the interface and reduce the carrier recombination loss.The optimized two-dimensional black phosphorus-CsPbI3 heterojunction all-inorganic PSC achieves a highest short-circuit current density of 19.3 mA cm-2 and PCE of 14.17%.(5)Inorganic perovskite CsPbI2Br thin films with gradient Te ion doping concentration were prepared by vapor deposition technology.On this basis,a novel inorganic perovskite P-N junction structure was constructed.The results demonstrate that Te doping can change the carrier type of inorganic perovskite,transforming n-type inorganic perovskite into p-type inorganic perovskite.The constructed P-N junction shows a strong depleted built-in electric field which can promote the balanced transport of carriers under the synergistic effect of charge drift and diffusion.As a result,the electron and hole transport efficiency are reduced to 114.64 ps and 173.22 ps,respectively.In addition,the P-N junction presents gradient energy level arrangement,which solves the problem of energy level mismatch between inorganic perovskite active layer and hole transport layer,reduces the recombination loss in the process of hole transport,and finally obtains a high open circuit voltage of 1.34 V.The optimized P-N junction CsPbI2Br PSC has a highest PCE of 15.30%,and the large area(9.6 cm2)inorganic perovskite cell module has achieved an excellent PCE of more than 10%.