Interaction Between Perovskite Film And Hole-transporting Layer And Its Influence On Device Performance

The perovskite solar cells have lots of advantages such as solution-processed,low-cost,unique optoelectronic properties.During the past ten years,the certified efficiency of perovskite solar cell(<1 cm²)has surpassed 25%,which is expected to be commercialized.The perovskite layer is the key to fabricate a high-efficiency and stable solar cell.However,the perovskite precursor maintains lots of groups which is chemical activity(such as amine)and the perovskite film needs a crystallizing procedure.Thus,it is important to focus on the interaction between the substrates and the active layer during the deposition of perovskite films.In this dissertation,I majored in the interaction between the perovskite film and the polymer hole-transporting layer and its influence on the device performance.Main results of this thesis are presented below:1.Revealing that the hole-transporting layer PEDOT:PSS which is in oxide state can be reduced by perovskite precursor and its influence on open-circuit voltage(V_OC).Firstly,we find that the perovskite solar cell with conventional structure fabricated by methylamine post-treatment shows a regular performance while the cell with inverted structure based on PEDOT:PSS substrate shows a poor performance.The reason is that the methylamine can reduce the PEDOT:PSS film when treating perovskite film,lowering the work function and conductivity of PEDOT:PSS.Further,we find that the MAI and perovskite precursor can also reduce the PEDOT:PSS,which enlarges the energy barrier between perovskite film and hole transporting layer.This is the reason why inverted perovskite solar cells based on PEDOT:PSS substrate typically show low VOC.2.Using the neutral conducting polymers(P3HT,PTB7,PTB7-Th)as hole transporting layer to replace PEDOT:PSS.Through the air-plasma treatment,the contact angle of polymer is reduced,which is benefit for deposition of high-quality perovskite films.The device based on these polymers shows a higher V_OC(from 0.88 V to over 1.00 V)and a higher PCE(from 13%to 17%),due to the non-reduction-active property.Meanwhile,the stability of devices also improves because of the hydrophobicity of neutral polymer.3.Explaining the vertical phase distribution of the quasi-two-dimensional perovskite film by sedimentation equilibrium.Also,we find that the vertical phase distribution of the quasi-two-dimensional perovskite depends on the substrate.When the substrate is glass,the quasi-two-dimensional perovskite shows a vertical phase distribution.However,when the substrate is PEDOT:PSS,the vertical phase distribution is disappeared.By modification PEDOT:PSS substrate with 4-bromobenzenediazonium tetrafluoroborate,we change the acidic PSS group into a neutral group.The quasi-two-dimensional perovskite film deposited on Br B-PEDOT:PSS substrate shows a desired vertical phase distribution.Thus,the solar cell show a higher V_OC(from 1.01 V to 1.11V)and PCE(from 12.29%to 13.74%).Through the transient absorption measurement,we find that the vertical phase distribution is benefit for the separation of excitons and transporting of charge.Meanwhile,the SCLC,C-V,EL measurements prove that the traps density is reduced in the perovskite film deposited on Br B-PEDOT:PSS,thus the energy loss is reduced.Moreover,the stability of device also improves because of the hydrophobicity of Br B-PEDOT:PSS.