Study On Highly Efficient And Stable Perovskite Solar Cells Based On Aromatic Hydrocarbons

In recent years,perovskite materials have been widely used in the field of solar cells due to their excellent carrier mobility,light absorption coefficient,and high defect tolerance.Currently,the power conversion efficiency（PCE）of perovskite solar cells（PSC）has reached 25.7%,almost equal to traditional silicon solar cells.Another advantage of perovskite materials is that they can be prepared by solution method,which greatly reduces the difficulty of their preparation.However,during the preparation process based on solution method,many defects are inevitably formed on the surface of perovskite thin films.This surface/interface defect state will become a non-radiative recombination center between perovskite and the transport layer,resulting in a serious loss of open circuit voltage(V_oc).Moreover,the existence of these defects will lead to a reduction in crystal quality and dislocation of the energy bands between the active layer and the charge transfer layer,which will seriously affect the transport of carriers.Therefore,how to passivate such defects has become a problem that must be solved.Here,we introduce the aromatic compound phenylalanine（PHE）as a passivation agent into perovskite solar cells.We mixed PHE with FAx MA1-x Pb Iy Br3-y perovskite at a concentration ratio of 0.2:1 to obtain a mixed precursor solution,and then obtained a denser perovskite film through a two-step spin coating method.We have prepared a perovskite solar cell based on this perovskite mixed solution,and the photoelectric conversion efficiency of the PHE optimized FAx MA1-x Pb Iy Br3-y perovskite battery has increased from 18.4%to 19.99%.Through the characterization of the thin film,it was found that the perovskite thin film obtained better compactness and significantly decreased roughness after PHE passivation.In addition,the addition of PHE can also increase the carrier lifetime of perovskite thin films and promote carrier transport.Based on FAPb I₃perovskite,we also simulated and calculated the defect formation energy and water oxygen adsorption energy of perovskite materials before and after optimization using density functional theory（DFT）and analyzed the optimization mechanism of PHE from the perspective of computational chemistry.Firstly,we calculated the binding energies of three different functional groups（-OH,-NH₃,=O）on the surface of perovskite on PHE and determined the binding mode dominated by oxygen double bonds（=O）.Then we constructed a very common iodine vacancy defect model to calculate the formation energy of iodine vacancy defects on the perovskite surface before and after PHE passivation.The calculation results show that PHE can significantly enhance the formation energy of iodine vacancy defects in perovskite,which is consistent with the device characterization results,proving the reliability of the simulation results.At the same time,we have demonstrated the effective barrier effect of PHE on water and oxygen by calculating the adsorption energy of perovskite materials before and after PHE passivation.In summary,we proposed a perovskite passivation project based on PHE,and demonstrated it through a combination of experimental characterization and software simulation,providing a new idea for the development of perovskite solar cells.