Study On Highly Efficient And Stable Perovskite Solar Cells

Organic metal halide perovskite solar cells?PSCs?have attracted widespread attention owing to their merits of solution processability,inexpensive materials,low temperature processing and further allowable deposition on flexible substrates.Most crucial is the high power conversion efficiency?PCE?more than 22%,which is approached rapidly within a few years.Although higher PCE has been obtained,many and basic issues and intrinsic mechanisms,such as controlling-sensitive crystallization process of the perovskite films,unstable device performance and lead toxicity,are still existing in PSCs.To address aforementioned issues,this thesis mainly focuses on improving the efficiency and the stability of PSCs simultaneously via effective interface and component engineerings.Additionally,the theis involves a challengeable study to fabricate highly efficient lead-less PSCs via partial substitution of lead using ecofriendly elements.1.We realized a good control of CH₃NH₃PbI_xCl_3-x crystallization by introducing cross-linking fullerene derivative?C-PCBSD?in perovskite precursors.Through an optimization of the crystallization in CH₃NH₃PbI_xCl_3-x:C-PCBSD films during annealing process,high efficiency PSCs with long-term stability were obtained.C-PCBSD was found to act as an electron acceptor in the CH₃NH₃PbI_xCl_3-x:C-PCBSD film to solve the problem of low electron extraction issue by effectively suppressing the shunt resistance and the leakage current in the devices.In addition,Pinhole free,the thermal crosslinking between perovskite and C-PCBSD resulted in high quality perovskite films with pinhole-free and large grain size.Importantly,the devices also demonstrated improved stability owing to the suppress of moisture an oxygen incursion by a C-PCBSD network.2.We developed a organic-inorganic hybrid hole-transporting material?HTM?in perovskite solar cells by doping copper salts?cuprous thiocyanate?CuSCN?or cuprous iodide?CuI??into 2,2,7,7-tetrakis?N,N-di-p-methoxyphenylamine?-9,9-spirobifluorene?Spiro-OMeTAD?based on a solution process.By copper salt doping,composite HTM with high hole mobility and good chemical stability was achieved.In details,it was found that the copper salt doping resulted in a significant increase in film conductivity and hole mobility of Spiro-OMeTAD:CuSCN?or Cu I?hybrid composite film,which in turn facilitated the hole transport and extraction characteristics.In addition,Spiro-OMeTAD:CuSCN hybrid film could inhibit film aggregation and reduce pinholes,leading to a stable perovskite-protection-layer owing to the resistance of water infiltration.3.A solution-processed C-PCBSD andgraphdiyne?GD?hybrid electron-transporting layer was developed to improve the charge transport characteristics and stability of PSCs.The hybrid electron-transporting layer possessed good electron transport properties and high film conductivity.It is found that the?-?stacking interaction between C-PCBSD and GD gave rise the ordered stacking of C-PCBSD molecules.C-PCBSD:GD hybrid films have the advantages of good electron mobility and efficient charge extraction,which is beneficial for the crystal growth of perovskite films.In addition,sturdy and compact network of C-PCBSD films provided enough solvent resistance to avoid interfacial infiltration.As a result,the perovskite devices delivered a PCE of 20.19%with obviously improved cell stability.4.Pb-Sn-Cu ternary metal perovskite absorber was developed to prepare lead-less PSCs.Non-toxic SnI₂ and CuBr₂ were utilized for a partial substitution of PbI₂.Pb-Sn-Cu perovskite films demonstrated high quality with improved grain size and increased film coverage.The behind origin of Sn²⁺and Cu²⁺substitution was investigated in detail.Sn substitution presented a red shift in absorption,whereas deteriorated perovskite degradation.Further Cu²⁺incorpration inactivated the traps at the crystal boundaries,improving the film morphology and crystallinity of the Pb-Sn perovskite.As a result,a PCE as high as 21.08%in Pb-Sn-Cu ternary metal perovskite solar cell was obtained.