NH_(4)PF_(6) assisted buried interface defect passivation for planar perovskite solar cells with efficiency exceeding 21%

The buried interface defects severely affect the further enhancements of efficiency and stability of SnO_(2)-based planar perovskite solar cells(PSCs).To well tackle this problem,we propose a passivation strategy employing NH_(4)PF_6 to modify the buried interface of perovskite layer((FAPbI_(3))_(0.85)(MAPbBr_(3))_(0.15) composition) in planar PSCs.After introducing NH_(4)PF_(6),the oxygen defects on the surface of SnO_(2) film are greatly restricted due to the coordinate interaction between fluorine atoms(F) in PF_(6)^(-)and undercoordinated Sn^(4+).Meanwhile,the hydrogen bonding interaction(N-H…I) between NH_(4)PF_(6) and PbI_(2) can passivate the non-radiative charge recombination sites,significantly optimizing the quality of perovskite film,as well as the charge transfer process at the SnO_(2)/perovskite interface.As a result,the NH_(4)PF_(6)-modified PSC obtains a champion power conversion efficiency(PCE) of 21.11%superior to the reference device(18.46%),and the device with an active area of 1 cm^(2) achieves a PCE as high as17.38%.Furthermore,the unencapsulated NH_(4)PF_(6)-modified PSCs show good humidity stability and retain about80% of the initial PCE after 1080 h aging at the relative humidity(RH) of 35% ± 5%.