Study Of Hole Transport Layer And Interface Modification In Perovskite Solar Cells

Perovskite solar cells（PSCs）have attracted widespread attention due to their high photovoltaic conversion efficiency,simple fabrication process,and relatively low cost.The device structure of PSCs mainly includes electron transport layer,perovskite absorber layer,hole transport layer,and metal electrode.The main role of the hole transport layer is to collect and transport holes and to protect the perovskite absorber layer from water and oxygen,which has a significant impact on the efficiency and long-term stability of PSCs.The weak hydrophobicity of the hole transport layer and interfacial defects with the perovskite layer will lead to degradation of device performance.Therefore,research on the stability of the hole transport layer and its interface is of great scientific significance and value for the preparation of high-efficiency and stable PSCs.In this thesis,the issues affecting the stability of PSCs related to the hole transport layer and its interface were systematically studied,including the development of a new hydrophobic hole dopant to replace the hygroscopic Li-TFSI/tBP doping system,the development of dopant-free hole transport materials to replace the doped Spiro-OMeTAD,and the introduction of a bifunctional interface modification material between the perovskite absorber layer and the hole transport layer.The detailed research contents and results are as follows:（1）Li-TFSI was modified by the host-guest coordination strategy,and a novel hydrophobic hole dopant[Li⁺（12C4）]TFSI^-was designed and prepared,which was used for Spiro-OMeTAD doping.It was found that Li⁺ion is encapsulated within the macrocycle of the crown ether to form[Li⁺（12C4）]cation,inhibiting the interaction of Li⁺with O₂and H₂O.[Li⁺（12C4）]TFSI^-has a lower highest occupied molecular orbital（HOMO）energy level,inducing the spontaneous charge transfer of Spiro-OMeTAD and avoiding the slow oxidation process exposed to air.The direct doping of[Li⁺（12C4）]TFSI^-and its passivation effect on surface ion defects of the perovskite provide higher hole transport efficiency for the device.Finally,PSCs doped with[Li⁺（12C4）]TFSI^-achieved an efficiency of 20.71%,which is higher than that of PSCs doped with Li-TFSI/tBP（19.46%）.Meanwhile,[Li⁺（12C4）]TFSI^-doped PSCs also exhibited excellent air stability and can still retain 92%of the initial efficiency after aging for 30 days,while PSCs doped with Li-TFSI/tBP only retained 54%of the initial efficiency under the same aging conditions.（2）A new hydrophobic Lewis acid dopant MTS-PF was developed to replace the Li-TFSI/tBP system for doping PTAA.It was found that MTS-PF has Lewis acid property,which could achieve efficient p-type doping to Lewis base PTAA.In addition,light could promote the reaction of MTS-PF doping PTAA,further promoting the generation of PTAA^·+radicals.Compared with the hole transport layer doped with Li-TFSI/tBP,the MTS-PF doped hole transport layer has lower HOMO energy levels and better hole transport performance.PSCs based on light-treated MTS-PF doping achieved the best efficiency of 21.32%,while the efficiency of PSCs doped with Li-TFSI/tBP was only 19.45%.Meanwhile,PSCs doped with MTS-PF exhibited excellent long-term stability,retaining an initial efficiency of 90%after aging for 30 days.（3）A bifunctional interface material,fluorinated polymer F-PTAA,was designed and prepared,which can modify the surface of perovskite and promote hole transfer at the perovskite/PTAA interface.It was found that the HOMO energy level of F-PTAA is located between the valence band of perovskite and the HOMO energy level of the hole transport layer,forming a gradient energy level that can more effectively separate and transfer holes,reduce carrier loss,and improve the open-circuit voltage of the device.In addition,the F atom in F-PTAA can act as a Lewis base to passivate Pb²⁺defects on the surface of perovskite,suppressing non-radiative recombination of charge carriers.Finally,PSCs modified with F-PTAA achieved higher efficiency（20.44%）and exhibited better long-term stability compared to PSCs without F-PTAA modification（18.15%）.After aging for 30 days,F-PTAA modified PSCs can still retained 85%of the initial efficiency.（4）Two dopant-free hole transport materials,WH-2 and WH-3,containing sulfur-rich DTF units and triphenylamine（TPA）were designed and prepared.It was found that the introduction of electron-donating DTF enhanced the electron-donating ability of TPA and intermolecular interactions,which facilitated theπ-πstacking of molecules and improved hole mobility.Finally,PSCs based on dopant-free WH-3 achieved an efficiency of up to 19.22%,which is comparable to PSCs based on Li-TFSI/tBP-doped Spiro-OMeTAD.Due to the fact that WH-3 does not require the hygroscopic Li-TFSI and volatile tBP,WH-3 film exhibited superior long-term stability compared to Spiro-OMeTAD film.PSCs based on dopant-free WH-3 still retained 97%of the initial efficiency after aging for 15 days,while PSCs based on doped Spiro-OMeTAD only retained 87%of the initial efficiency under the same aging conditions.