High-Performance Perovskite/Organic Tandem Solar Cells Fabrication And Their Performance Study

Benefit from the continuous development of new materials and improvement of device processes,organic and perovskite solar cells have achieved rapid development in recent years.The efficiency of small-area single-junction organic and perovskite solar cell had reached 18%and 25%,respectively.Tandem structure can overcome the insufficient response range of single-junction solar cell and therefore further improve the solar cell efficiency.In this thesis,improvement of the efficiency of organic/perovskite tandem/integrated device was achieved by carefully selection of proper materials and device process optimization.Furthermore,the working mechanism of the tandem/integrated devices was studied.In first part of this work,by integrating a large bandgap inorganic perovskite Cs Pb I₂Br with two narrow bandgap bulk heterojunction(BHJ)layers,PM6:Y6 and PTB7-Th:O6T-4F,we have successfully demonstrated a monolithic perovskite/organic tandem cell with power conversion efficiency(PCE)over 18%.In addition,based on the photovoltaic performance parameters that have already been achieved in state-of-the-art organic and perovskite solar cells,we further evaluate the potential PCE of the perovskite/organic tandem cells,showing a maximum calculated PCE of over 31%when the bandgaps of the subcells are optimized.This work paves the way for the development of hybrid tandem solar cells with promising performance.In the second part of this work,we utilize Cs_0.2FA_0.8Pb(I_0.6Br_0.4)₃ to replace Cs Pb I₂Br as perovskite system,and utilize an all-solution processed bilayer HTL composed of PDCBT and modified PEDOT:PSS(PEDOT:PSS,IPA and n-Bu OH(v:v:v=1:2:1))to replace the vacuum processed metal oxide Mo O₃ HTL to fabricate single-junction perovskite solar cells.It was found that PEDOT:PSS solution with addition of IPA and n-Bu OH can be easily spincoated on the PDCBT surface.With the introduction of PEDOT:PSS layer,the built-in electric field and carrier extraction density of the device was increased,which improve both the device V_ocand J_sc.This work not only provides more options to design HTL for perovskite solar cells,but also lays the foundation for fabricating tandem solar cells using all-solution processes.In the third part of this work,the compositions of Cs_0.2FA_0.8Pb I_3-xBr_x(x=1.2,1.32)was fine-tuned X site halogen ions ratio to achieve an optimal energy level matching between the perovskite and BHJ layer.Furthermore,a modify HTL was developed by further introducing20%of highly conductive PH1000 solution into dilution PEDOT:PSS AI 4083 solution to improve HTL conductive and alleviate S-shape curve.Finally,we successful fabricate two kind solution processed tandem devices and increase the efficiency to 15%.Since PEDOT:PSS can protect the bottom layer from being erode during the solution processing of top layers,this work provides an effective strategy to obtain an solution processed inter-connection junction for perovskite/organic tandem devices.It therefore lays the foundation for full solution processing of perovskite/organic tandem solar cells.In the fourth part of this work,we aiming to further simplify the tandem structure design by removing the interconnection layer between the organic BHJ and perovskite layers.Therefore,the BHJ layer was directly spin cast on the perovskite layer to fabricate an integrated solar cell.Here we choose PM6:Y6 binary and PM6:Y6:PC₇₀BM ternary blending system as the organic layer and combine with Cs_0.2FA_0.8Pb(I_0.6Br_0.4)₃hybrid perovskite to form the integrated light harvesting layer.The result show that the organic donor material in the BHJ act as hole transport layer and transport hole carrier from the perovskite film.The electron-hole mismatch of excitons(exciton transport imbalance;carrier density imbalance)is the critical factor that determine the formation of S-shape curve from the J-V test.by reducing the ratio of acceptor to improve hole transport ability for perovskite,the S-curve property can be gradually eliminated.This work not only provide an optimization strategy to design and fabricate integrated solar cells,the preliminary working mechanism of the integrated solar cells was also investigated to better stand the corresponding device physics.