Investigation On Interface Modification Of Perovskite Solar Cells Based On Organic Ammonium Salt

After more than ten years of development,the efficiency and stability of organic-inorganic hybrid perovskite solar cells have been greatly improved,so it is hopeful to realize industrialization.How to further improve the performance of perovskite solar cells is still a matter of great concern.Because Sn O₂ has the advantages of low preparation temperature,high electron mobility,and insensitive to ultraviolet light,it is considered to be the most suitable electron transport material.However,there may be energy level mismatch and defects at the Sn O₂/perovskite interface due to the poor compatibility between Sn O₂ and perovskite.In addition,perovskite films prepared by solution method will have a large number of defects on their surface and grain boundaries.The existence of these problems will limit the improvement of device performance.Herein,this thesis focuses on the modification of the interface related to perovskite layer through organic ammonium salt,so as to improve device performance by adjusting the interface energy level,passivating the interface defects,and selecting the interface modification material with appropriate structure,which can be divided into the following four parts.（1）Effect of hydrazine hydrochloride（N₂H₅Cl）on energy level regulation at Sn O₂/perovskite interface.The charges are seriously recombined at the Sn O₂/perovskite interface due to the mismatch of energy level,which reduces the device performance.Based on these knowledge,we use hydrophilic N₂H₅Cl to modify the Sn O₂ surface.It is found that N₂H₅Cl can increase the work function of Sn O₂,which can not only promote the electron transport due to the improvement of interface energy level,but also effectively increase the V_oc due to the elimination of interface energy level barrier.In addition,N₂H₅Cl modification also increases the wettability of Sn O ₂,resulting in the enlargement of perovskite grains and the reduction of grain boundaries,which means the decrease of grain boundary defects.The efficiency of the device is finally increased from 19.43%to 21.17%due to the improvement of interface energy level and the reduction of grain boundaries.（2）Effect of a zwitterion（DETAPMP）on interface passivation at Sn O₂/perovskite interface.To study the effect of interface defect passivation on device performance,we use a zwitterion（DETAPMP）to modify Sn O₂,and replace FAPb I₃with MAPb I₃ to eliminate the influence of interface energy level barrier on device performance.X-ray photoelectron spectroscopy shows that DETAPMP can not only passivate the oxygen vacancy defects on Sn O₂ films through Sn-O-P bond,but also promote the enlargement of perovskite grains through the electrostatic interaction between ammonium ion and Pb I₃^-,resulting increased average J_sc from 19.63 to 21.58m A/cm².（3）Effect of steric hindrance of butylammonium iodide（BAI）on the modification at the Spiro-OMe TA/perovskite interface.To select the appropriate structure of interface modification materials,we used BAI with different steric hindrance to modify the surface of perovskite.X-ray diffraction spectra show that BAI can react with Pb I₂ to form quasi-2D perovskite to improve the device performance.However,the device efficiency will gradually increase from 17.39%to 20.67%with the decrease of BAI steric hindrance.Through a series of characterization,it is found that this is due to the steric hindrance hindering the diffusion of BAI to the perovskite grain boundary,which reduces the passivation of perovskite grain boundary and the transport of interfacial holes.（4）Effect of chain length of short chain ammonium salt on the modification at the Spiro-OMe TA/perovskite interface.In the third work,we found that the efficiency of the device with BAI modifications was not significantly improved,which may be the longer chain length of BA⁺hindering the transport of interfacial holes.To further improve the efficiency,we used a series of short chain ammonium salts with different chain lengths to modify the perovskite surface.The first principle calculation shows that these short chain ammonium salts can be adsorbed on the perovskite surface,which indicates that they can passivate perovskite defects,so as to improve the performance of perovskite solar cells.Indeed,with the decrease of ammonium salt chain length,the device efficiency will gradually increase from 20.56%to 21.74%.Through a series of characterization,it is found that this is due to the decrease of ammonium salt chain length to facilitate the transport of interfacial holes.