Investigation On Materials And Interface For High-efficiency And Stable Perovskite Solar Cells

Solar cells have unique advantages which reduce dependence on fossil fuels for energy generation and promote the development strategy of the“carbon neutral”in China.Among them,the perovskite solar cells have become a research hotspot due to their excellent photoelectric conversion efficiency and low preparation cost.However,photovoltaic device efficiency remains below theoretical limits,and the stability of perovskite-based cell devices has hampered industrial application development.Interface defects and mismatching strain,according to current findings,are major variables affecting the efficiency and stability of PSCs.For this difficult problem,interfacial defects and mismatching strain in perovskite interfaces are investigated at the atomic level,including their impact on carrier recombination,charge transport,band alignment,and instability.These theoretical bases are applied to a specific experiment to verify our views.Subsequently,all-inorganic perovskite was studied for the impacts of Cs Br passivation and mismatching strain,which induced crystallization quality of Cs Pb Br₃.The main research contents and innovative achievements of this paper are as follows:（1）Electrical properties on defects at the MAPb I₃ surface.The structural and electrical properties of the MAPb I₃ surface were investigated using the first-principles methods,and the inhibitory effect of passivation engineering on the defects of the MAPb I₃ surface was studied.The results show that the passivated surface exhibits high structural stability,which is independent of surface termination and defect types.The bandgap and band offset of defective perovskite surface is determined by the charge transfer from passivation which is related to the production of valence electron and electronegativity.The bandgap and band offset of defective perovskite surface is determined by the charge transfer from passivation which is related to the production of valence electron and electronegativity.Such mechanisms and characters are further confirmed by the device simulation.（2）Investigation of termination and defects at the MAPb I₃/SnO₂ interface.The interfacial structure and transport properties of MAPb I₃/SnO₂ interfaces on various terminations and passivated conditions have been investigated comprehensively by density functional theory and experiment.The results show that the formation of the MAPb I₃/SnO₂interface weakens gap states induced by MAPb I₃ surfaces.The Pb I-O interface is more beneficial for hole blocking and electron transporting due to the largest condition band offset compared to the others.Moreover,it exhibits a larger electrostatic potential difference compared with the MAPb I₃/Ti O₂ interface,leading to a higher electron transfer efficiency.Hence,higher power conversion efficiency has been achieved based on MAPb I₃/SnO₂compared to MAPb I₃/Ti O₂ structure in experiments.In addition,MAPb I₃/SnO₂ interfaces with Pb I terminations are more stable than those with MAI terminations,suggesting the Pb I₂layer may be preferentially formed on the SnO₂ substrate during the MAPb I₃ fabrication process.Using density functional theory combined with ab initio molecular dynamics,we have comprehensively investigated the performance enhancement mechanism of the device after surface reconstruction by passivating different halogen groups（ie F,Cl）at the ETL/perovskite interface.We demonstrated that the halogen group at the ETL layer could stabilize the geometric structure of the perovskite surface by balancing the interfacial interaction,ionic migration,and lead iodide framework.Even though halogen passivation respectively decreases and increases interface charge transfer at the O and SnO-terminated MAPb I₃/SnO₂ interfaces,halogen passivation optimized surface reconstruction can theoretically relieve interface carrier recombination according to the changes in CBOs generated by halogen passivation.Furthermore,the interface carrier recombination of the MAPb I₃/SnO₂ interface is also connected to the interfacial gap states,which are smaller for O-terminated MAPb I₃/SnO₂ interfaces with halogen passivation induced surface reconstruction but larger for SnO-terminated.（3）Investigation of termination and mismatch staring at the MAPb I₃/Ni O interface.The structures and electrical properties of MAI-O,MAI-Ni,Pb I-O,and Pb I-Ni interfaces were investigated using the first principles and device simulation.The results show that the Pb I terminations are beneficial for structure stability due to the weaker binding energy at the MAPb I₃/Ni O interface.Forming MAPb I₃/Ni O interface increase the Pb-I bond lengths by the MAPb I₃ surfaces.The Pb I-O interface is more beneficial for hole blocking and electron transporting due to the largest valence band offset compared to the others.The electrical properties of the perovskite solar cell with MAPb I₃/Ni O interface were simulated using the Silvaco software.This J-V curve further reflects the advantages in structural and electrical performance of the Pb I termination.we determined the valance band offset of MAPb I₃/Ni O interface decreases（increases）in perovskite surface with tensile（compressive）stress,respectively.But the Ni O surface with stress is reversed.（4）Investigation on Cs Br passivation and the adapted ETL for Cs Pb Br₃ perovskite solar cell.Due to the solubility difference between Cs Br and Pb Br₂,the crystalline quality of Cs Pb Br₃ films was seriously harmed.Cs Br passivation was employed to effectively control the phase separation in Cs Pb Br₃ films during the preparation process.At the same time,different electron transport layer materials were introduced to explore the effect of the underlying substrate on the crystalline quality of perovskite thin films.It was found that the deposition of Cs Pb Br₃film on Ti O₂ can improve the device properties,due to there being a suitable conduction band offset between Ti O₂ and Cs Pb Br₃.with its power conversion efficiency achieving a high of 9.48%and a high open-circuit voltage of 1.54 V.In addition,the unpackaged device maintains 98% device efficiency in the air.