Theroretical Investigation Of Photoelectrical Properties For Metal-free Sensitizers And Hole-transporting Materials

Dye-sensitized solar cells and perovskite solar cells play important roles in human production and life due to the advantages of simple preparation process,easy processing,light weight and low cost.The influence of inserted thiophene into the??-A'-??-bridge on photovoltaic performances of sensitizer are investigated using the density functional theory?DFT?and its time-dependent density functional theory?TD-DFT?methods.The geometries,electronic properties,spectral properties and hole transport properties of hole-transporting materials are investigated by introducting conjugated core and aromatic heterocycles,using density functional theory coupled with Marcus theory and Einstein relation.The main purpose of this paper is to theoretically study and explain the influence of molecular structure on the properties of materials,which provides an effective strategy and reliable theoretical guidance for the experimental synthesis of these materials.The major content and results are listed following:In Chapter 1,the development and research status of solar cells are mainly introduced.Moreover,we provide the device structures and their working principle of dye-sensitized solar cells and perovskite solar cells.As well as the sensitizers,hole-transporting materials,the basic issue and prospects of dye-sensitized solar cells and perovskite solar cell are presented.In Chapter 2,we expound the main theories for computation in this work,which include DFT,TD-DFT and Marcus theory.In addition,the main parameters of dye-sensitized solar cells and perovskite solar cell are also introduced in this chapter.In Chapter 3,a series of metal-free D-?-A'-?-A type organic dyes have been designed by inserting one or two thiophene between the??-A'-??-bridge and the donor and/or acceptor moieties based on BZTP-1.The influence of inserted thiophene into the??-A'-??-bridge on photovoltaic performances of sensitizer is investigated in detail using the density functional theory?DFT?and its time-dependent density functional theory?TD-DFT?methods.Calculated results show that increasing the length of the conjugated-linker leads to a high planarity and very narrow HOMO-LUMO energy gap.Especially,dye T-T-BZTP-T-T that forms by inserting two thiophenes into two sides of BZTP exhibits the most obvious red-shifted and the strongest absorption,which leads to a high V_oc.Moreover,we find that these dyes show a good character of electron injection and dye regeneration owing to the ideal?G_inject,?_normal and?G_reg.Therefore,the insertion of thiophene into the??-A'-??-bridge has a better influence on photovoltaic performance of designed dyes compared with BZTP-1.In Chapter 4,conjugated bifluorenylidene and naphthalene central core are introduced into hole-transporting materials DT1 and DT2 to replace the spiro-core of reported,high-efficient FDT.Effects of conjugated core on the geometrics,electronic properties and hole transport properties are investigated by using density functional theory coupled with Marcus theory and Einstein relation.Calculated results show that DT1 and DT2 have lower HOMO levels than FDT,which indicates that the perovskite solar cells with conjugated hole-transporting materials can have higher open-circuit voltages.The introduction of conjugated core is beneficial to the more efficient face-to-face packing pattern of dimer,resulting in a larger intermolecular electronic coupling.Importantly,it is found that DT1 and DT2 exhibit relatively higher hole mobilities than FDT owing to the larger electronic coupling.Therefore,enhanced hole transport ability can be achieved by switching from spiro-core to conjugated core.The present work provides new strategy to improve the hole transport properties of conjugated small molecule-based hole-transporting materials.In Chapter 5,three aromatic heterocycles are introduced into the hole-transporting materials S101 containing the Silafluorene core,respectively,to form three new hole-transporting molecules S-O,S-S and S-Se.Under the new theoretical calculation method,the influence of aromatic heterocycles spacer on the geometries,electronic properties and hole transport properties of hole-transporting materials are investigated in detail by using DFT,Marcus theory and Einstein relation.Calculated results show that the HOMO energy levels of S-O,S-S and S-Se are lower than that of S101.It indicates that aromatic heterocycles spacer introduced into hole-transporting materials can improve the open-circuit voltage of perovskite solar cells.The more efficient intermolecular interactions of dimer are formed by the introduction of aromatic heterocycles spacer into the three hole-transporting molecule,resulting in a larger intermolecular electronic coupling.The hole mobility of S-O,S-S and S-Se are higher that of S101.Importantly,an obvious regularity are found,their hole mobility gradually decreased with the increase of atomic number of aromatic heterocycles.Therefore,the introduction of aromatic heterocycles into the Silafluorene core can enhance the hole transport properties of hole-transporting materials.The current research provides a new direction to improve the hole transport properties of Silafluorene-based hole-transporting materials.