Research On Crystallization Regulation And Interfacial Passivation Of Perovskite Solar Cells

In recent years,the energy problem is becoming more and more serious,which promotes the study of green and clean energy.Solar energy is an inexhaustible green and clean energy source.Solar cells are devices that convert solar energy into electric energy by photovoltaic effect.Perovskite solar cells belong to the third generation of solar cells,which has the advantages of high efficiency,low cost and simple process,and has rapidly developed into one of the most popular research fields.At present,perovskite cells still have problems of poor stability and large area preparation difficulties.At present,this field mainly focuses on perovskite film growth,electron transport layer regulation,defect passivation and other aspects of research.As the core component of perovskite solar cells,the crystal quality of perovskite thin films directly affects the photoelectric performance of perovskite cells.Improving the crystal quality and reducing defects is an effective way to improve the efficiency and stability of devices.The preparation method of perovskite films plays a decisive role in the crystallinity,compactness and grain size,and thus affects the device performance.At present,the preparation methods of perovskite films mainly include spin coating method,two-step solution method,vapor deposition method and gas phase assisted solution method,among which spin coating method is the most commonly used.However,due to the rapid crystallization rate of perovskite films prepared by spinning coating,the obtained films tend to have smaller grain size and higher grain boundary density,which leads to the increase of the density of defective states,and thus affects the photoelectric performance of batteries.In addition,there are a lot of defects at the interface of perovskite cell structure.Interface defect passivation is an effective method to improve the performance of perovskite solar cells.Good interface contact can increase the open circuit voltage(V_OC)and filling factor（FF）of the device.Therefore,the research in this paper focuses on the crystal property regulation of perovskite thin film and the passivation of the electron transport layer/perovskite thin film interface,so as to improve the photoelectric performance of perovskite thin film and realize the improvement of the photoelectric conversion efficiency and stability of the battery.The main research contents include the following two aspects:（1）The method of autoclave assisted crystal growth of perovskite film was proposed in this study.The perovskite precursor films after spin coating were pre-annealed and crystallized in autoclave to obtain high quality perovskite films.The average grain size of perovskite films prepared by preannealing at 60℃for 3min and annealing at 100℃in autoclave for 1 h is increased from 255.70 nm to641.66 nm by the method of annealing at 100℃for 1 h.The XRD results show that the PbI₂diffraction peak of 12.7°basically disappears,indicating that most PbI₂has been transformed into perovskite phase.The stronger perovskite diffraction peak indicates that the perovskite film has a more uniform crystal orientation.Ultraviolet-visible absorption spectra show that it has stronger absorption capacity to incident light.The root-mean-square roughness of perovskite film decreases from23.65 nm to 22.60 nm.The higher PL peak indicated that the defects of perovskite films were reduced,which was consistent with SCLC results.TRPL test results show that the average carrier life increases from 66.41 ns to 95.49 ns,indicating that the defects of perovskite films are reduced and carrier recombination is inhibited.The photoelectric conversion efficiency of perovskite solar cells is increased from 17.30%to 18.96%.The initial efficiency was increased from 86%to90%after 240 hours of unpackaged storage in N₂glove box.（2）TiO₂electron transport layer/perovskite film interface passivated by potassium chloride.By adjusting the concentration of potassium chloride solution,the influence of different concentration of potassium chloride on the performance of perovskite solar cells was explored.The root-mean-square roughness of TiO₂films modified with potassium chloride（5 mg/mL）decreases from 14.65 nm to 14.22 nm,and the surface current increases from 282.11 PA to 329.34 PA.The root-mean-square roughness of the perovskite film decreases from 26.49 nm to21.03 nm,and the surface current increases from 268.50 PA to 319.06 PA.The diffraction peak of perovskite is enhanced and the crystal quality is better.Enhanced light absorption capacity;Carrier recombination is inhibited and carrier extraction ability is enhanced.The characteristic peak of Pb 4f moves 0.05 eV towards the direction of binding energy change,and the characteristic peak of I 3d moves 0.07 eV towards the direction of binding energy change.The larger ion binding energy is beneficial to improve the stability of perovskite structure.The photoelectric conversion efficiency of perovskite solar cells is increased from17.17%to 18.47%.The initial efficiency was increased from 86%to 91%after 240hours of unpackaged storage in N₂glove box.