Research On Highly Efficient And Stable All-inorganic Perovskite Solar Cells

Thanks to the excellent photovoltaic properties of the perovskite materials,including tunable band gaps,long carrier diffusion lengths,and high absorption coefficient,perovskite solar cells(PSCs)have made rapid developments in the field of photovoltaics in recent years.Among the perovskite family,all-inorganic cesium lead halide perovskites have also received much attention because of their excellent thermal stability and good photoelectric properties.In the field of all-inorganic perovskite solar cells,remarkable progress has been made in improvement of the photoelectric conversion efficiency(PCE).All-inorganic perovskite solar cells have achieved rapid development in photoelectric conversion efficiency,but their commercialization process is limited to a certain extent due to the fact that perovskite materials are prone to phase transition at room temperature,which leads to the attenuation of device performance.In this thesis,relevant research has been carried out on the stability improvement of all-inorganic perovskite materials at room temperature and the enhancement of the PSC performance and stability.The purpose is to explore the relationship between the crystal structure of perovskite materials and thermodynamic stability,and to improve the environmental stability of the PSCs while ensuring excellent photoelectric performance.First,the approach for the fabrication of stable CsPbI3-xBrx(x<1)films at low temperature was proposed.By adding excess CsBr into the CsPbI3 precursor solution,microstrain was induced in the CsPbI3 lattice,thereby facilitating the stability of cubic CsPbI3 phase at room temperature.The introduction of CsBr partially doped Br-into the CsPbI3 lattice,and the remaining Br" entered into the CsI lattice to form CsI1-yBry.With further characterization of the high-resolution transmission electron microscopy(HRTEM),it was observed that CsI1-yBry is distributed around the cubic structure of CsPbI3-xBrx,which limits the size of CsPbI3-xBrx particles to tens of nanometers.The reduction in grain size can effectively reduce the Gibbs free energy of the CsPbI3-xBrx lattice,thereby improving the thermodynamic stability of CsPbI3-xBrx at room temperature.The results showed that the introduction of a certain concentration of CsBr can effectively improve the crystalline properties of CsPbI3-xBrx,improve the film quality,and passivate the defects within the film.At the optimal CsBr concentration(0.5M),the optimized solar cell achieved the power conversion efficiency to be 10.92%.This work provided an effective method to stabilize the cubic CsPbl3-xBrx(x<1)phase at low temperature.On the basis of the CsI1-yBryCsPbI3-xBrx system,the films were treated by a moisture treatment.The synergistic effect of water was used to improve the crystallization property of CsI1-yBry/CsPbI3-xBrx film,thus high quality films and excellent photoelectric performance were obtained.It was observed by HRTEM that the CsI1-yBry/CsPI3-xBrx structure can be gradually evolved during the moisture treatment,that was,CSI1-yBry can be gradually transited to CsPbI3-xBrx.Further molecular dynamics simulations showed that moisture induces ion migration at the interface of CsI1-yBry/CsPbI3-xBrx,and Pb2+ions near the interface can be bonded with I-or Br-ions in CsI1-yBry,and new PbX6 octahedron was formed.The results showed that the film morphology was greatly improved and the defects in the film were passivated,which was conductive to the improvement of the film quality.Based on this process,the PCE of the PSC has increased significantly from 10.89%to 13.09%by the moisture treatment,in which the open circuit voltage(Voc)was increased from 0.97 V to 1.10 V,and the fill factor(FF)was increased from 69.09 to 76.54%.An all-inorganic 0/3D Cs4Pb(IBr)6/CsPbI3-xBrxheterostructure film was fabricated by carefully adjusting the molar ratio of Cs+and Pb2+ions in the precursor solution and controlling the crystal growth conditions.Scanning electron microscope(SEM)and electron backscatter diffraction(EBSD)results jointly demonstrated the distribution of 0D Cs4Pb(IBr)6 within the 0D/3D film.The introduction of the 0D structure not only improved the morphology of the film,but also induced the(001)plane preferential orientation of the 3D CsPbI3-xrBrx.The(040)0D//(001)3D interface of the two heterostructures observed by HRTEM well demonstrated the good matching characteristics of the 0D and 3D crystals.The introduction of 0D Cs4Pb(IBr)6 effectively passivated the defects within the film,suppressed non-radiative recombination across the interface.Compared with the control 3D PSC,the PCE of the PSC based on the 0D/3D heterojunction achieved a significant improvement from 4.64%to 14.77%.The 1 cm2-large area PSCs based on the 0D/3D heterostructure obtained a PCE of 10.52%.In addition,the PSCs based on the 0D/3D film showed significantly enhanced stability.After 60 days of storage under nitrogen atmosphere,PCE of the 0D/3D PSCs can maintain more than 90%of the initial value.All-inorganic Cs2PbI2Cl2/CsPbI2.5Br0.5 heterostructure films were fabricated by controlling the crystal growth conditions and adjusting the ratio of Cs+and Cl-ions in the precursor solution.Combining the results of SEM and EBSD,it was observed that 2D Cs2PbI2Cl2 was distributed at the grain boundaries of the CsPbI2.5Br0.5 large grains within the film.The results showed that the introduction of 2D Cs2Pbl2Cl2 induced the preferred orientation of the CsPbI2.5Br0.5 crystal structure on the(001)plane.The smooth transition region between the 2D and 3D crystals was observed by HRTEM,indicating that a 2D/3D heterostructure was formed between the(003)2D//(001)3D interface.Due to the lattice matching characteristics of 2D and 3D crystals,the introduction of 2D Cs2PbI2Cl2 effectively passivated defects and suppressed the non-radiative recombination within the film.The PCE of 2D/3D PSC was achieved to be 15.09%,of which Jsc is significantly increased to 16.62 mA cm2,and Voc was 1.21 V,and FF was 75.17%.In addition,the large-area PSCs of 1 and 2 cm2 were fabricated,achieving PCEs to be 12.74%and 10.01%,respectively.The introduction of the 2D Cs2PbI2Cl2 significantly improved the moisture and thermal stability of the PSCs.After 60 days storage at room temperature in a nitrogen atmosphere,the PSCs maintained their initial efficiency of 95.3%;under 70±10%relative humidity contidition,the PSCs were placed under continuous heating at 80℃,and PCE of the 2D/3D PSC can maintain 80%of its original PCE for 12 h.