Research On Hole-Transporting Materials Of Antimony Selenosulfide Solar Cells

As a type of one-dimensional Ⅴ2-Ⅵ3 inorganic semiconductor compound,antimony selenosulfide,Sb₂（S,Se）₃,displays superior optoelectronic properties such as strong absorption coefficient at visible range(>104 cm^-1),easily tunable bandgap in range of 1.1～1.7 eV,and high theoretical maximum efficiency approaching 33%.In terms of practical photovoltaic applications,Sb₂（S,Se）₃ is relatively low-cost,environmentally-friendly,earth-abundant,and stable against moisture and air.Consequently,Sb₂（S,Se）₃ solar cells have been demonstrated the great potential for the scientific research and the application prospect.In principle,interface materials as well as high-quality light-absorbed materials,which determine whether the carriers generated by the light-absorbed materials could be effectively transferred to the electrodes,play an indispensable role in obtaining the highly efficient solar cells.To this end,we focus on boosting the power conversation efficiency（PCE）of Sb₂（S,Se）₃ solar cells and then conduct correlative research in this dissertation.At first,we optimize the crystallinity and micromorphology of Sb₂（S,Se）₃ thin films by alkali metal doping and acquire a device efficiency of 6.56%.On top of that,perovskite quantum dots（QDs）are exploited as a highly stable hole-transporting material（HTM）in Sb₂（S,Se）₃ solar cells,resulting in an efficiency of 7.82%.Subsequently,we develop a low-cost,efficient organic small molecule as the HTM of Sb₂（S,Se）₃ solar cells and further raise the PCE to 9.7%.This dissertation consists of five chapters,the main contents are as follows.1.In the first chapter,the development history and physical basis of solar cells are initially summarized.Afterwards,the basic properties of Sb₂（S,Se）₃ materials and the research status of Sb₂（S,Se）₃ solar cells are deeply analyzed,including preparation methods,device types,interface materials,etc.Finally,the great significance of developing Sb₂（S,Se）₃ solar cells and the scientific problems to be solved at present are highlighted.2.In the second chapter,to promote the properties of Sb₂S₃ thin films is studied.We systematically investigate the effects of all the alkali ions doping on the crystal structure,microstructure,photoelectric properties of Sb₂S₃ thin films and the performance of Sb₂S₃ solar cells.The doping of heavy alkali-metals ions（K⁺,Rb⁺and Cs⁺）,especially for Cs⁺ doping,significantly enhance the crystallinity,compactness,and flatness of Sb₂S₃ thin films.Thus,the light absorption intensity of Sb₂S₃ thin films is strengthened.Upon Cs⁺ doping,the Fermi levels of Sb₂S₃ thin films have an upward shift,leading to the increase of open-circuit voltage.Eventually,a 6.56%efficiency of planar-heterojunction Sb₂S₃ solar cell is achieved by Cs⁺-doping.3.In the third chapter,we develop the lead halogen perovskite CsPbBr₃ and CH₃NH₃PbBr₃ QDs as the HTMs of Sb₂（S,Se）₃ solar cells,respectively.By regulating the surface ligand concentration of perovskite QDs and the preparation process of perovskite QDs films,the dense and uniform perovskite QDs films with the ultrathin thickness of approximate 25 nm are capped on the surface of Sb₂（S,Se）₃ as the HTMs.These HTMs enable to effectively extract and transport the photogenerated holes from Sb₂（S,Se）₃ film and inhibit carrier recombination at the back electrode interface,resulting in a better PCE of 7.82%for the CsPbBr3 QDs-based device.Importantly,after storing in the ambient air with relative humidity（RH）>15%and room temperature（RT）for 100 days,the unencapsulated Sb₂（S,Se）₃ solar cells with these perovskite QDs as HTMs exhibit no PCE degradation.This study not only broadens the application range of perovskite materials,but also provides a unique scheme for the efficiency increase of Sb₂（S,Se）₃ solar cells.4.In order to further boost the efficiency of Sb₂（S,Se）₃ solar cells,we exploit a low-cost,stable,and efficient dithieno[3,2-b:2’,3’-d]pyrrole-cored organic small molecular（denoted as DTPThMe-ThTPA）as the HTM.Compared with widely employed spiro-OMeTAD,DTPThMe-ThTPA demonstrates the higher hole mobility and better capacity of extraction and transmission of light-generated holes.Moreover,the Sb₂（S,Se）₃/DTPThMe-ThTPA heterojunction forms the bidentate-chelating effect between thiophene and Sb on the interfaces,which is highly desirable for diminishing the interface defect states and enabling high hole-extracted efficiency.Benefitting from these results,the champion DTPThMe-ThTPA-based Sb₂（S,Se）₃ solar cells achieved a PCE value of 9.7%.Furthermore,the devices with DTPThMe-ThTPA show the better stability than these of the spiro-OMeTAD-based devices in the ambient air.The passivation mechanism of interface defects between the thiophene units and Sb₂（S,Se）₃ provides a feasible idea for exploitering more efficient and doping-free HTMs.5.In the fifth chapter,the main achievements in this doctoral thesis are summarized,and the unsolved problems in this study are pointed out as well.Finally,we propose some research directions and suggestions in order to obtain more in-depth understanding of the material properties of Sb₂（S,Se）₃ and boost the performance of Sb₂（S,Se）₃ solar cells in turn.