Study On The Performance Regulation Of Perovskite Solar Cells Using Multifunctional Radical Molecules

After nearly 11 years of development,the certified power conversion efficiency(PCE)of perovskite solar cells(PSCs)has been increased to 25.2%.However,the long-term stability remains an issue impeding the commercialization of PSCs.Generally,polycrystalline perovskite thin films have many defects,which affect the optoelectronic performance and stability of the devices.In addition,PSCs with high-performance employ the 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene(Spiro-OMeTAD)as hole transport material.Due to low conductivity of pristine Spiro-OMeTAD,bis(trifluoromethane)sulfonimide lithium salt(Li-TFSI)and 4-tert-butylpyridine(t BP)are often added to increase its conductivity.However,Li-TFSI is easy to agglomerate in Spiro-OMeTAD hole transport layer(HTL),resulting in holes in the HTL,which not only affects the electrical properties of the HTL,but also affects the long-term stability of the devices.Here,radical molecules were used to modify perovskite and Spiro-OMeTAD,respectively,obtaining efficient and stable PSCs.The main contents and conclusions are as follows:(1)Regulate the perovskite layer.We explored the effects of three kinds of radical small molecules with different functional groups on the optoelectronic properties of PSCs.Among them,the perovskite films with larger grains,fewer grain boundaries,better crystallinity and lower density of defect states were obtained by modifying perovskite with 2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO),which inhibited the charge recombination and promoted the extraction and transport of carriers.The optimized TEMPO modified PSCs achieved a power conversion efficiency of 20.73%.(2)Regulate the hole transport layer.We employed the non-conjugated radical polymer poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl)(PTEO)to modify Spiro-OMeTAD.Compaired to that of the unmodified Spiro-OMeTAD HTL,the hole mobility and conductivity of the modified Spiro-OMeTAD HTL increased.The valence band of the modified Spiro-OMeTAD HTL more matched with that of the perovskite layer,which promoted the hole transport.Additionly,the radical polymer could effectively inhibit the accumulation of lithium salts in Spiro-OMeTAD HTL and synergistically passivate the perovskite layer/HTL interface and HTL/Au electrode interface.The optimized PTEO modified PSCs achieved a power conversion efficiency of 21.18%.After aged under low humidity and dark conditions for 10000 h,aged at 85 ? for 1000 h,100 thermal cycles(-40 ??85 ?)and continuous light aging at the maximum power point for 1000 h,the PSCs modified with PTEO respectively maintained 90%,98%,93% and 98% of its original PCE.