Photoelectric Characteristics And Device Optimization Of Lead-free Perovskite Solar Cells

Perovskite solar cells have become a hot field in recent years due to their high absorption coefficient,adjustable band gap,excellent carrier transport capacity,rapid improvement efficiency and simple preparation process.However,traditional perovskite solar cells contain heavy metal lead which is harmful to the environment.Considering the environmental friendliness requirements of solar cells,the further industrial application of such solar cells has been greatly limited.In order to continue the development of this superior solar cell,the development and utilization of lead-free perovskites is imperative.A series of novel copper-doped manganese-based lead-free perovskite single crystals of MA₂Mn_1-xCu_xCl₄ were synthesized by slowly cooling the volatile solvent.Thermogravimetric analysis of single crystals shows that copper doping is not conducive to stability improvement;MA₂Mn_1-xCu_xCl₄ film was prepared by one-step spin coating method,and the phase structure and UV-Vis absorption spectrum of the film were analyzed.The results show that the pure manganese-based perovskite film has Better surface coverage,a small amount of copper doping is beneficial to improve the light absorption intensity of the material.Then we assembled complete MA₂Mn_1-xCu_xCl₄ photovoltaic devices and tested its electrochemical impedance spectroscopy,linear sweep voltammetry and its photocurrent density-time characteristics under simulated sunlight and different wavelengths of monochromatic light.We found that it has significant photocurrent response characteristics,and then we compared the optoelectronic properties of different doped materials.Based on the study of copper-doped manganese-based lead-free perovskites,we used the same method to prepare a series of MA₂Zn_1-xCu_xCl₄ copper-doped zinc-based lead-free perovskite single crystals,thin films and corresponding photovoltaic devices.Through thermogravimetric analysis of single crystals,it is found that pure zinc-based and a small amount of copper-doped perovskites have higher thermal stability.Scanning electron microscopy of the films show that copper doping significantly affects the thickness and morphology of the films.By analyzing the UV-Vis-NIR absorption spectrum and diffuse reflectance spectrum of the films,it obtains the highest light absorption when the copper content is about 50%;The photocurrent density-time characteristics of the devices under simulated sunlight shows that the pure zinc-based and a small amount of copper-doped devices have a stronger photocurrent response.Further electrochemical impedance spectroscopy and linear sweep voltammetry tests show that the electron transport capacity and photon utilization of copper-containing devices are not as good as those of pure zinc-based devices.Due to the high PCE of tin-based perovskite solar cells in the field of lead-free perovskites,studies on tin-based perovskites has been continuously developed.However,due to lack of theoretical guidance it is difficult to make progress in experiments.In order to promote the further development of tin-based perovskite solar cells,we initially used statistical analysis to systematically study the factors affecting the performance of such devices.Through systematic analysis of the collected literature data,we found that different materials significantly affects the PCE and V_oc of the device,but have little effect on J_sc and FF.We can also optimize device combinations by comparing device composition and fabrication processes.In addition,tin-lead mixed perovskites have a wide absorption wavelength,and the V_oc,J_sc and PCE are obviously superior to the pure tin-based devices,which is of great significance for the development of less lead perovskites.However,this statistical analysis method is still in the preliminary exploration stage,and the relevant data and experimental influencing factors are insufficiently collected and need to be further improved.