New Hole Transport Layer For Metal Chalcogenide Solar Cells

Energy is the foundation of the development of human society.Clean energy has become the key of improving energy structure and achieving sustainable development.Solar energy is rich in resources and is recognized as one of the most potential clean energy sources.Due to the excellent photoelectric properties of metal chalcogenides,they have received extensive attention from researchers.Among them,the Sb2(SxSe1-x)3 has a high absorption coefficient(>105 cm-1),and the adjustable band gap(1.1-1.8 eV)by changing the atomic ratio of S/Se and the high abundance of elements,which are environmentally friendly.These advantages make Sb2(SxSe1-x)3 solar cells promising for industrialization.However,it still faces some challenges.The first is the limitation of hole transport materials.Hole transport materials(HTM)are not only used to transport holes,but also play a particularly important role in inhibiting charge recombination.The highest efficiency Sb2(SxSe1-x)3 solar cell to date is achieved using Spiro-OMeTAD,an organic hole transport material,but due to the space created by the sp3 hybridization of N atoms and the special structure Steric hindrance,undoped Spiro-OMeTAD has relatively low hole mobility(～10-4 cm2 V-1S-1)and low conductivity(～10-5 Scm2).In order to overcome these problems,doped Heterolithium salt(Li-TFSI)and tetra-tert-butylpyridine(TBP)increase its electrical conductivity and thereby improve photovoltaic performance.However,Li-TFSI is deliquescent and hygroscopic,which will seriously damage the function of organic hole transport layer as a result,the efficiency of the device is reduced.Meanwhile,the use of inorganic hole transport materials such as PbS,CuSCN,V2O5,etc.have problems such as band mismatching and bad interface,which obtain the bad battery efficiency.Therefore,the focus of this research is to develop a hole transport layer with high stability,excellent performance,and easily prepared,and apply it to metal chalcogenide solar cells.Chapter 1 systematically summarizes the theoretical knowledge related to photovoltaic devices.The main content includes energy band theory,solar cell principles,the meaning and calculation methods of various performance parameters,and briefly summarizes the development history and current status of mainstream photovoltaic devices.Chapter 2 chapter systematically summarizes the main preparation methods and key technical points of each functional layer of Sb2(S,Se)3 solar cells,and briefly introduces the optical and electrical characterization methods of solar cell devices to pave the way for subsequent analysis.Chapter 3 We dissolved Copper(Ⅱ)2,9,16,23-tetra-tert-butyl-29H,31H-phthalocy anine powders into chlorobenzene solvent and demonstrated this CuPc film as the effective HTL of Sb2(S,Se)3 solar cells.Treating the complete device with low-temperature heating,the tremendous cracks and pinholes in CuPc film are marvelously disappeared accompanying by a metal gold diffusion into CuPc HTL.Furthermore,doping the CuPc HTL with tiny 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ),the champion Sb2(S,Se)3 solar cells with a PCE of 8.6%was obtained.Importantly,Sb2(S,Se)3 solar cells based on F4-TCNQ-doping CuPc HTL show good long-term stability.Chapter 4 introduces in detail the substitution of hydrophobic additives such as Li-TFSI and TBP in the hole layer of Spiro-OMeTAD by hydrophobic organic small molecule F4-TCNQ,which greatly improves the conductivity of the hole transport layer of Spiro-OMeTAD and the water and oxygen stability of the battery.Chapter 5 summarizes and analyzes the topics of high-performance hole transport materials applied to metal chalcogenide compounds studied during the master’s degree,and puts forward some hypotheses and considerations for subsequent research.