Stable 24.29-Efficiency FA_(0.85)MA_(0.15)PbI_3 Perovskite Solar Cells Enabled by Methyl Haloacetate-Lead Dimer Complex

摘要

Formamidinium methylammonium lead iodide (FAMAPbI_3) perovskite hasbeen intensively investigated as a potential photovoltaic material because ithas higher phase stability than its pure FAPbI_3 perovskite counterpart. However,its power conversion efficiency (PCE) is significantly inferior due to itshigh density of surface detects and mismatched energy level with electrodes.Herein, a bifunctional passivator, methyl haloacetate (methyl chloroacetate,(MClA), methyl bromoacetate (MBrA)), is designed to reduce defect density,to tune the energy levels and to improve interfacial charge extraction in theFAMAPbI_3 perovskite cell by synergistic passivation of both CO groupsand halogen anions. As predicted by modeling undercoordinated Pb~(2+), theMBrA shows a very strong interaction with Pb~(2+) by forming a dimer complex([C_6H_(10)Br_2O_4Pb]~(2+)), which effectively reduces the defect density of the perovskiteand suppresses non-radiative recombination. Meanwhile, the Br? in MBrApassivates iodine-deficient defects. Consequently, the MBrA-modified devicepresents an excellent PCE of 24.29%, an open-circuit voltage (V_(oc)) of 1.18 V (Vocloss ≈ 0.38 V), which is one of the highest PCEs among all FAMAPbI_3-basedperovskite solar cells reported to date. Furthermore, the MBrA-modified deviceswithout any encapsulation exhibit remarkable long-term stability with only 9%of PCE loss after exposure to ambient air for 1440 h.