Deep and shallow level defect passivation via fluoromethyl phosphonate for high performance air-processed perovskite solar cells

Air-processed perovskite solar cells (PSCs) with high performance are considered to be the inevitable trend of low-cost commercial manufacturing. Nevertheless, the deep- and shallow-level defects of humid-air-processed perovskite films are the main sources of photoelectric conversion efficiency (PCE) deficit. Herein, a difluoromethyl phosphonic acid diethyl ester (2F-PAE) with tri-chelation sites is implanted into perovskite absorber to passivate uncoordinated Pb²⁺/Pb clusters and raise formation energies of vacancies in perovskite films. The P = O/C-O groups in 2F-PAE offer tri-chelation sites to bind tightly with uncoordinated Pb²⁺/Pb clusters, which passivates deep-level defects and regulates perovskite crystallization. -CF₂ groups in 2F-PAE generate electrostatic interaction with FA⁺, which helps to passivate shallow-level defects. The formation energies of Pb, I and FA vacancies can be increased by more than twice under the synergistic passivation of P = O, C-O and -CF₂. Thus, the open-circuit voltage (V_OC) of the humid-air-processed PSCs with 2F-PAE increases to 1.188 V. 2F-PAE passivated PSCs dramatically improve the PCE from 20.54 % to 23.69 %. PSCs using 2F-PAE display excellent moisture and thermal stability, retaining 82 % of its initial efficiency after 1500 h under continuous illumination, while the control PSCs maintain only 44 %. This strategy offers crucial insights for selecting multifunctional molecules to boost the performance of PSCs.