The Modification Of Bi-base Polymetallic On The Hole Layers And Photovoltaic Performance Research On Perovskite Solar Cells

Perovskite solar cells(PSCs)have obtained significant progress in the past decade,where a high PCE of 25.5%has been achieved from the initial 3.8%.Currently,Spiro-OMe TAD is the most widely employed to assemble high-efficiency PSCs devices.However,the hole mobility and conductivity of pristine Spiro-OMe TAD is commonly low,which needs to be oxidized to perform excellent electrochemical performance.Besides,Li-TFSI and TBP could lead to other problems,such as pinholes and ion migration,which would cause the performance and stability degradation of PSCs.In order to promote the commercialization of PSCs,it is necessary to develop suitable substitutes or additives to improve the photovoltaic performance and long-term stability of PSCs.Polyoxometalates(POMs)and ternary semiconductor have great potential research value in the field of optoelectronics due to low fabricating cost and high thermal stability.Therefore,vacant Keggin type POMs and Ag Bi Se₂ nanoparticles had been synthesized via a facile low temperature aqueous solution route to modify or replace the hole transport layer(HTL),respectively.Thanks to the excellent electrochemical properties of the material itself,the overall performance of PSCs has been improved significantly.Because of the excellent oxidizing ability,trilacunary Keggin type POMs(Bi W₉)can directly oxidize Spiro-OMe TAD under the inert atmosphere.Under the electronic transaction between Bi W₉ and Spiro-OMe TAD,the electrical properties of the HTL have been improved.Thus,the devices based on Bi W₉ obtain a champion power conversion efficiency(PCE)of 19.41%,which exceeded that of the blank device(18.48%).It has been proved that the energy level of Bi W₉ matches the perovskite more closely.With the doping of Bi W₉,the extraction of holes inside the PSCs is more efficient and faster,and the recombination behavior of carriers also has been suppressed.Bi W₉ improves the surface morphology of the HTL,as well as inhibiting the direct contact of moisture in the air with the perovskite,thereby reducing the degradation rate of the perovskite and increasing the long-term stability of PSCs.As a result,the PCE of PSCs based on Bi W₉ still maintains about 85%of its initial PCE at ambient condition(25?,RH?30%),where the PCE of blank lost more than 35%after one month.In an attempt to analyze the effects of transition metal structure on the properties of POMs and PSCs,three lacunary Keggin type POMs(Bi W₁₀M)were prepared by doping different transition metal elements in Bi W₉.Due to excellent electron accept ability and strong oxidizing ability,transition metal elements could oxidize Spiro-OMe TAD with Bi W₉ in an inert atmosphere together.The doping of transition metal elements improves the photoelectric properties of POMs effectively,as well as the PSCs based on Bi W₁₀M.The improved photovoltaic performance could be attributed to the faster hole separation and extraction,which is caused by excellent carrier conductivity of transition metal elements.The champion PCEs of PSCs based on Bi W₁₀Mn,Bi W₁₀Co,Bi W₁₀Zn are 20.31%,20.12%and 20.01%,respectively,which are higher than that of the blank(18.48%).POMs could adjust oxidation ability,energy level and conductivity by introducing different transition metal elements.Under the same valence state,the oxidation ability of transition metal elements is related to the ability of capturing electrons.The valence electron configuration of Mn^II is 3d5,which makes it easier to seize or lose electrons.Therefore,Bi W₁₀Mn shows the strongest oxidation ability,as well as the best photovoltaic performance of PSCs based on Bi W₁₀Mn.Besides,the hydrophobicity and resistance to moisture of HTL based on Bi W₁₀M had increased.The PSCs modified by Bi W₁₀M could maintain90%initial PCE at ambient condition(25?,RH?30%)after one month.The AgBiSe₂ nanoparticles(high purity,good crystallinity and small particle size)were synthesized firstly by a facile solution method under a low temperature,which is different from solid-state sintering method(high temperatures,long reaction times,impurities and large particle size).This way provides a new idea for the synthesis of other I-V-VI₂ ternary semiconductor materials.The Ag Bi Se₂ thin film,which was prepared by vacuum evaporation,has strong light absorption intensity in the range of400-800 nm.After annealing treatment,the photoelectric performance of the Ag Bi Se₂film has been improved due to the denser and smoother surface morphology,which has fewer defects.Furthermore,the Ag Bi Se₂ film was deposited on the surface of the perovskite as the HTL by spin coating to evaluate its effects on PSCs.Because of the appropriate valence band position,which is matched with the perovskite,Ag Bi Se₂film could extract and transport holes and suppress the recombination behavior of charges between the interfaces effectively,thereby enhancing the photoelectric properties of PSCs.As a result,the champion PCE of PSCs based on Ag Bi Se₂ film is3.85%,which is nearly doubled(the best PCE of blank devices is 1.97%).