Fabrication And Investigation Of Perovskite Solar Cells Based On Metal Oxide Transport-layers

Perovskite solar cells?PSCs?,with its high absorption coefficient,excellent carrier transmission performance,high open circuit voltage and simple fabrication technology,have gained great attention of researchers.Since they were firstly used as semiconductor sensitizer in dye-sensitized solar cells in 2009,the efficiency of PSCs has achieved 22.1%,which have shown great prospect in solar cell field.But the PSCs also exist many problems such as the unstability of device,which is the key problem restricting the development of PSCs.Factors that affecting the stability of PSCs can mainly divided into the stability of perovskite absorbing layer and the stability of the transport layer materials.When exposed into the polar solvent,organic-inorganic halide perovskite absorption layer will be soonly decomposed.And the traditional organic materials transport layer are also unstable,which will also affect the stability of the devices.In this thesis,we use stable inorganic semiconductor materials to replace the traditional organic material as the transport layers to increase the stability of PSCs.However,the traditional inorganic semiconductor materials,such as NiO_x and ZnO with low concentration of carriers,which go against for improving the performance of PSCs.The most commom method of increasing carrier concentration is doping elements in intrinsic semiconductor.In this paper,we use NiO_x and ZnO to replace Spiro-OMeTAD and PCBM as transport layer materials,respectively.In order to improve both carrier transmission capacity and the stability of the cells,we introduce p-type doped in NiO_x and n-type doped ZnO respectively.Thus realizing the fabrication of PSCs based on inorganic metal oxide.Our work is divided into the following three parts:?1?NiO_x is direct band-gap semiconductor with 4.0 eV band gap.NiO_x thin film shows p-type semiconductor characteristic as the existence of Ni²⁺vacancy in its crystal lattice,which makes it appropriate for the inorganic hole-transporting layers?HTLs?in PSCs.But intrinsic NiO_x thin film has low concentration of carriers.So the efficiency of PSCs is very low when using intrinsic NiO_x as hole transport layer,especially in short-circuit current.Therefore,we used the sol-gel method to co-doped Li element and Cu elements into NiO_x thin film,and applied them as hole transport layer into PSCs.The Cu doping can mainly improve the carrier concentration and the conductivity of NiO_x thin film.And Li doping can improve the crystalline of thin film and increase the transmittance of NiO_x thin film.So we use intrinsic NiO_x thin film,Cu-doped NiO_x thin film,Li,Cu-codoped NiO_x thin film as HTLs to fabricate PSCs devices.Finding that the efficiency of PSCs based on Li,Cu-codoped NiO_x thin film HTL is as high as 14.53%,while the efficiency of PSCs used intrinsic NiO_x thin film as HTL is only 7.94%.This phenomenon is mainly caused by the increasing of short circuit current and fill factor.So far in this chapter,we put forward by Li,Cu-codoped NiO_x thin film can preferably transmission carrier,so as to optimize the performance of the cells.?2?The intrinsic ZnO is a direct band gap n-type semiconductor with band-gap 3.37 eV.Compared to TiO₂,ZnO has higher carrier mobility and is general used in PSCs as electronic transport layer?ETL?.But carrier concentration of intrinsic ZnO thin film is also insufficient for high efficiency PSCs,so we want to improve the carrier concentration by doping element.So far,the n-type doping is a major mean of improving carrier concentration of intrinsic ZnO semiconductor.In this chapter,we choose In as the doping element.We use one-pot method for the synthesis of different In-doped concentration of In-doped ZnO nanocrystals,and then carry on the element analysis and the morphology characterization.Finding that the actual doping content of In element is very close to theoretical value,which shows the high doped-rate in ZnO nanocrystals of In element.The efficiency of PSCs used 3%In-doped ZnO thin film as ETL is 14.53%,while the efficiency of PSCs used intrinsic ZnO thin film as ETL is only 7.94%.This phenomenon illustrates that In-doping method can improve the carrier transmission ability of ZnO thin film,so as to improve the performance of PSCs.?3?The third part work is based on the above two parts,we used Li,Cu-codoped NiO_x thin film as HTL and 3%In-doped ZnO thin film as ETL,respectively.In this approach,We fabricated metal oxide transport layer PSCs.Not only improving the the efficiency of PSCs,but also improving the stability of PSCs.