Interfacial Engineering For High Performance Solution-Processable Perovskite Solar Cells

Since the 21 st century,the energy crisis has become increasingly evident with the large consumption of non-renewable energy.Therefore,the full development and utilization of renewable energy have become one of the main ways to solve the energy crisis.Among the many renewable energy sources,solar energy is the most prominent since it is never exhausted and can continuously provide the energy to human.Therefore,the development of effective photovoltaic technology by converting solar energy to electrical energy is very crucial.Solar cells can directly convert solar energy into electrical energy,which is of great significance for solving energy depletion and alleviating environmental pollution.Although silicon solar cells have been fully put into use with high power conversion efficiencies(PCE)more than 20%,their large-scale applications are constrained by the issues of high cost,heavy pollution,and unsustainable development.It is particularly important to further develop efficient and stable solar cells.In recent years,perovskite solar cells(PSCs)attact many atttentions with surprising efficiency rising over 22% wthin a few years.However,perovskite solar cells still have some problems such as high cost,poor stability,and complicated preparation processes.In order to solve these issues,we aim to improve the device performance of perovskite solar cells by investigating the structure and operational mechanism from the perspective of interface engineering.First,authors study MAPb I3-XCl X based inverted perovskite solar cells and theirs working mechanism.The most commonly used hole-transporting layer(HTL)in inverted PSCs is full name(PEDOT:PSS).Although PEDOT:PSS-based PSCs have achieved PCE more than 15%,the efficiency is unsatisfied and the cell stability is limited due to the acidic,strong oxidizing,and easily deliquescent nature of the PEDOT:PSS.In order to further improve the device performance,we used two methods to modify and improve the HTLs of inverted perovskite solar cells.(1)Authors combine the advantages of PEDOT:PSS and water-soluble copper phthalocyanine material Copper phthalocyanine-3,4?,4??,4???-tetrasulfonated acid tetra sodium salt(TS-Cu Pc)by using mixed TS-Cu Pc and PEDOT:PSS as HTL in inverted PSCs.The atomic force microscope(AFM)and scanning electron microscopy(SEM)were used to study the morphology of the HTL and the corresponding perovskite films.Electrochemical impedance spectroscopy(EIS),steady-state photoluminescence(PL),and ultraviolet-visible absorption(UV/vis)were used to investigate the charge extraction and transport properties in perovskite solar cells.For the cell stability,authors carried out a detailed study from the viewpoint of the contact angles of the HTLs and the corresponding perovskite films,and the p H values of the hybrid HTL precursor.Consequently,the resulting device delivered a PCE as high as 17.29% with good stability by using TS-Cu Pc doped PEDOT:PSS HTL.(2)Although the device performance could be improved by using TS-Cu Pc doped PEDOT:PSS as HTL,the presence of PEDOT:PSS would still corrode the ITO electrode.In order to avoid this phenomenon,it is imperative to find a new hole-transporting material instead of PEDOT:PSS.Authors developed doped TS-Cu Pc by organic small molecule F4-TCNQ and/or metal oxide Mo O3 as the hole-transporting layer in inverted PSCs.It was found that the device based on the HTL of F4-TCNQ doped TS-Cu Pc presented a PCE of 16.14%.In contrast,the device based on the HTL of Mo O3-doped TS-Cu Pc just demonstrated comparable PCE as the PEDOT:PSS based one.The evaluations of hole mobility,external quantum efficiency(EQE),X-ray diffraction(XRD)and contact angle revealed that F4-TCNQ doped TS-Cu Pc showed large4 hole mobility and higher external quantum efficiency compared to Mo O3-doped TS-Cu Pc,resultedin the improvement of overall performance including efficiency and stability.In short,authors provide a new choice for the hole-transporting layer of perovskite solar cells by the lower cost,simple fabrication process and outstanding device performance of F4-TCNQ-doped TS-Cu Pc.Second,authors also studied MAPb I3 based normal PSCs and their working mechanism.Meanwhile,the most widely used HTL in normal PSCs is 2,2?,7,7?-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9?-spirobifluorene(Spiro-OMe TAD).Although Spiro-OMe TAD-based noraml PSCs have achieved PCE over 20%,the stability and repeatability of the device is restricted by the easy oxidation nature of Spiro-OMe TAD.In order to improve the PCE and stability of the Spiro-OMe TAD-based noraml PSCs,authors fabricated the hole-modifying layer by combining the advantages of F4-TCNQ and TS-Cu Pc.The hole-modifying layer can not only block the entrance of oxygen and vapour but also supply a more appropriate energy alignment.After the application of the hole-modifying layer,the PCE has achieved 20.16% and better stability.Furthermore,authors investigated the characteristics of the hole-modifying layer F4-TCNQ:TS-Cu Pc by transmission electron microscopy(TEM),Leica microscopy,external quantum efficiency(EQE),steady-state photocurrent.