A Study On The Preparation And Performance Of Solar Cells Based On Organic-Inorganic Hybrid Perovskite

Organic-inorganic hybrid perovskite solar cells are considered to be one of the most promising candidates for industrialization in the new generation of photovoltaics,because of their high coversion efficiency and simple fabrication process.Although perovskite solar cells have achieved great success in the laboratory,they are still facing some critical problems that restrict their practical process.Among them,the design of higy-performance and high-stability buffer layer materials,the preparation of high-quality perovskite precursor solution,and the controlled deposition of large-area perovskite film are particularly important.To solve these problems,this thesis focuses on the improvement of material synthesis and devices fabrication,and reveals the related mechanisms.The organic small molecule spiro-OMeTAD is widely used as a hole transport material in perovskite solar cells,but its limited electric conductivity might be a bottle-neck challenge in the efficiency improvement of perovskite solar cells.In this thesis,a low-cost technique is developed to improve the performance of spiro-OMeTAD layer by doping it with commercially available benzoyl peroxide(BPO).Conductivity measurement,absorption spectroscopical and fluorescence spectroscopical results demonstrate that BPO is an effective oxidation doping spiro-OMeTAD,and enhance hole extraction.The BPO doped spiro-OMeTAD is used as a hole transport layer in the fabrication of perovskite solar cells,which exhibit excellent photoelectric performance,stability and reproducibility.High-quality and concentrated precursor solution are essential for the fabrication of perovskite solar cells.This thesis reports a simple and efficient of preparing the high concentration methylammonium triiodoplumbate(MAPbI3)precursor solution by using MAPbI3 crystal instead of conventional lead iodide and methyllammonium iodide blend.The MAPbI3 concentration of the precursor solution is easily and accurately adjusted from zero up to 1.64 M.The investigation on the dissolution process of the MAPbI3 crystal reveals that the concentrated solution of MAPbI3 in DMF is metastable,and transition from the concentrated solution to solvated intermediate MAPbI3·DMF determines the solubility of MAPbI3 in DMF.The MAPbI3 crystal as a raw material can suppress the transition and increase the stability of the concentrated solution,and a highest power conversion efficiency of 20.7%is achieved on corresponding solar cells.Based on the above results,a new low-boiling-point solvent system composed of methylamine solution in ethanol and tetrahydrofuran is designed for methylammonium lead iodide precursor solution.Concentrated methylammonium lead iodide precursor solutions with a concentration of 2.1 M are obtained,and smooth and compact methylammonium lead iodide films with the area up to 600 cm2 are prepared by one-step directly spin-coating or blade-coating the precursor solution at room temperature Optical microscope of the crystal growth process indicate that the rapid evaporation of the solvent and strong interaction between methylamine and methylammonium lead iodide lead to a high crystal nucleus density and intermediate-free crystallization path,and consequently bring a compact and smooth film.The high-quality methylammonium lead iodide films show excellent photovoltaic performance in conventional mesoporous solar cells with efficiencies of 20.0%(0.1 cm2)and 15.6%(10 cm2).The low-temperature prepared zinc oxide(ZnO)is a high-performance electron transport layer(ETL)with extraordinary electron mobility and suitable work function However,the Lewis basic nature of ZnO surface leads to deprotonation of the perovskite layer,resulting in serious degradation of the devices.This thesis develops a new method of co-sputtering to prepare zinc oxide-tin oxide(ZSO)composite film at low temperature.The ratio of zinc oxide and tin oxide was precisely controlled by adjusting the sputtering conditions,which can effectively control the surface alkilinity,avoid the decomposition of perovskite layer,and adjust the energy levels.The conversion efficiency of perovskite solar cells was up to 19.94%based on ZSO ETL,and it keeps unchanged after continuous operation for 30 days,displaying good stability.