The Research On Hole Transporting Materials And Interfaces For Efficient And Stable Perovskite Solar Cells

As one of the most promising photovoltaic devices,organo-lead halide perovskite solar cells（PSCs）have attracted tremendous attention owing to their excellent photovoltaic properties,low-cost,ease of fabrication and rapid increasing power conversion efficiencies（PCEs）.However,despite the excellent PCE that have recently been achieved（a certified PCE of 25.2%）,the device stability is still a challenge for the commercialization of PSCs.Besides,the scale-up manufacturing of PSCs and the recycle and treatment of the perovskite modules and toxic waste are also need further study and adaptation.In this dissertation,we intensively studied several different hole transport materials（HTMs）and appropriately modified the interface between the perovskite and HTM or the HTM and metal electrode,thus obtaining PSCs with high efficiency and stability.The typical research achievements are summarized as follow:（1）P-type PbS thin film fabricated by vacuum thermal-evaporation could be an alternative promising material in PSCs as buffer layer between HTM and metal electrode.We demonstrated that the Spiro-OMeTAD/PbS bilayer exhibited a higher hole extraction efficiency than the bare Spiro-OMeTAD,which result in an enhanced charge extraction kinetics between perovskite and HTL,and a more balanced electron and hole transfer.As a result,the PSCs with compact PbS buffer layer have shown a significantly improved photovoltaic performance with respect to the reference cells.Besides,the hydrophobic nature and dense morphology of PbS enable it to protect the perovskite absorber and Spiro-OMeTAD layer from degradation caused by moisture and ions migration,thus improving the device stability.The device with the structure of FTO/SnO₂/PCBM/perovskite/Spiro-OMeTAD/PbS/Au shows a champion efficiency of 19.58%for reverse scan and 18%for steady-state,and an excellent long-term stability and thermal stability.（2）A novel heavy atom metallophthalocyanine derivative with octamethyl substituents,octamethyl-substituted palladium（II）phthalocyanine（PdMe₂Pc）,was synthesized and shown promise as a HTM in PSCs.Our research demonstrated that when deposited atop perovskite the PdMe₂Pc could form a face-on molecular alignment which resulting in high hole mobility.The strong spin-orbit coupling effect introduced by heavy atom of Pd leads to a longer carrier lifetime of PdMe₂Pc than CuMe₂Pc meanwhile without significantly decreasing its carrier mobility,resulting in a longer carrier diffusion length of PdMe₂Pc than CuMe₂Pc.This property is very favorable for HTM applications in photovoltaic devices because it can reduce the interfacial charge recombination.Besides,the condense and hydrophobic surface of PdMe₂Pc made the device more stable.Perovskite solar cells with structure of FTO/SnO₂/6,6-phenyl-C61-butyric acid methyl ester（PCBM）/perovskite/MPcs（M=Cu,Pd）/Au were fabricated and tested.As expected,the devices based on PdMe₂Pc exhibited a higher PCE of 16.28%than those based on CuMe₂Pc（15.58%）,and shown good moisture stability（maintaining 96%of its initial performance after 600 h of storage in ambient air）.（3）A synergistically combined strategy consisting of triple interface treatments—including post-annealing,O₂-plasma,and potassium chloride treatments—is employed to modulate the optoelectronic properties of the sputtered NiO_x films and hence improved the efficiency of the resultant PSCs.We demonstrated that the extra oxygen introduced by post-annealing and O₂-plasma treatment significantly increased the film conductivity and carrier density.Furthermore,the O₂-plasma treatment helped to shift the NiO_x surface work function and thus decreased the defect recombination at the NiO_x/perovskite interface.Additionally,the KCl passivation process was adopted before the O₂-plasma treatment to mitigate the plasma damages on the NiO_x surface.The presence of KCl crystals helped to improve the hole extraction efficiency from perovskite to NiO_x and thus reduced the J-V hysteresis.The resultant devices with the modified sputtered NiO_x HTM delivered a highest stabilized efficiency of 18.7%with good reproducibility and stability.