Solution-processed Sb₂Se₃ Bulk/Nano Structures For Solar Cells

It is a growing trend in the field of solar cells to produce efficient and stable photovoltaic materials and devices by inexpensive solution-processing methods.Antimony selenide is a promising light-absorbing material for solar cells because of its ideal band gap matching solar spectrum,high absorption coefficient and great stability.However,the efficiency of the Sb2Se3 solar cells is still much lower than the ShockleyQueisser limit of 32%.It is urgent to develop the solution-processing approaches to obtain high-quality Sb2Se3-based heterojunction material system,in order to achieve the photovoltaic devices with a potential application.The dissertation aims to develop the solution-processing methods to prepare quality Sb2Se3-based heterojunctions for solar cells.The main research activities and results in this dissertaion are summarized as follows:1.Using tiny(<10 nm)Sb2S3 crystals as heterogeneous epitaxial nuclei,[001]oriented Sb2Se3 nanorod array is prepared on TiO2 nanoparticle film by a solutionprocessing method,creating an Sb2Se3/TiO2-based nanoarray heterojunction(Sb2Se3/TiO2-NHJ).The Sb2Se3 nanorod array film consists of[001]-oriented Sb2Se3 single-crystalline nanorods of a quadrilateral prismatic shape on the TiO2 nanoparticle film.Sb2Se3 nanorods grow along[001]direction,where the crystal orientation is determined by the[211]/[221]-orientation of the tiny Sb2S3 seeds epitaxially nucleated by TiO2(101)crystal plane.The length of the Sb2Se3 nanorods is controlled by the repeat number of spin coating/annealing process.A novel Sb2Se3/TiO2-NHJ solar cell structured with FTO/TiO2/Sb2Se3/PTB7-th/Au is prepared by utilizing organic conjugated polymer PTB7-th as hole transporting material,and achieves a power conversion efficiency of 1.07%.2.Using large(200-400 nm)Sb2S3 crystals as heterogeneous epitaxial nuclei,[001]-oriented monolayer of Sb2Se3 single-crystalline bulk cuboids is prepared on TiO2 nanoparticle film by a solution-processing method,creating an Sb2S3/TiO2-bulk/nanoplanar heterojunction(Sb2Se3/TiO2-BnPHJ).Sb2Se3 cuboids grow along[001]direction,where the crystal orientation is determined by the[211]/[221]-orientation of the large Sb2S3 seeds epitaxially nucleated by TiO2(101)crystal plane.The Sb2Se3 layer thickness is controlled by the repeat number of spin coating/annealing process.A novel Sb2Se3/TiO2-BnPHJ solar cell structured with FTO/TiO2/Sb2Se3/PTB7-th/Au is prepared by utilizing organic conjugated polymer PTB7-th as hole transporting material,and achieves a power conversion eficiency of 1.65%.3.The CdCl2 treatment at the TiO2/Sb2Se3 interfacei boosts the efficiency of planar heteojunction solar cell based the Sb2Se3 film grown without seed induction up to 4.93%.Results show that the CdCl2 treatment enhances the[hkl]-orientation of the resulting Sb2Se3 layer and the heterojunction quality,so as to promote the charge transfer in the bulk film and at interfaces and reduce the carrier recombination in the device,consequently leading to an improved the device performance.