Theoretical Design And Investigation Of Charge Transporting Materials For Perovskite Solar Cells

Perovskite solar cells(PSCs)have a multitude of potential advantages that have attracted intensive attention in the field of solar cells,such as inexpensive cost,straightforward synthesis and relatively decent photoelectric conversion efficiency(PCE).Universally,the important ingredient in PSCs is charge transporting material(CTM),including hole transporting material(HTM)and electron transporting material(ETM),which play a vital role in the overall performance of device.This article mainly explores these two types of material molecules.First of all,based on density functional theory(DFT),time-dependent density functional theory(TD-DFT),Marcus charge transfer theory,Einstein equation and molecular dynamics(MD).The geometric structure,photoelectric property,hole transport property,solubility,and thermal stability of all material molecules were studied.This article mainly theoretically explores the physical mechanism between the molecular structures and relative properties,which can provide effective strategy and appropriate theoretical guidance for developing highly efficient and stable charge transporting materials.The primary content of this article is as follows:In Chapter 1,there are a few reports that the optoelectronic properties of the methoxyaniline-based hole-transporting materials are intimately correlated with the positions of methoxy substituents(-OMe).To dig into this phenomenon deeply,we theoretically design five new hole transporting materials based on FDT through altering the positions of methoxy substituents.Then,the electronic structures,optical properties,and hole transport properties are investigated at the molecular level via density functional theory and Marcus theory coupled to Einstein relation.The calculated results reveal that the derivatives with o-OMe or m-OMe substituent exhibit lower HOMO levels,favoring higher open-circuit voltages.Most importantly,benefitting from greaterorder and compact intermolecular stacking,the derivatives with o-OMe substituents(F1,F3)as HTMs exhibit relatively decent hole mobilities,which are two or three orders of magnitude higher than that of FDT.Quantum chemistry calculation and crystal packing arrangement simulation indicate that-OMe substituents at different positions show disparate orientations and thus affect the molecular stacking.Our work reiterates the importance of molecular configuration for the materials properties and provides those who are engaged in upgrading the performances of hole transporting materials a new train of thought and tactics with ease and economy.In Chapter 2,the construction of state-of-the-art charge transporting materials(CTMs)is challenging in modulating molecular configurations for simultaneously achieving higher thermal stability and appreciable solution processability.Herein,NDI-ID is served as a theoretical model to investigate the influence of molecular structure on the tradeoff between thermal stability and solubility.We show that,compared with alkyl substituted analogs,the thermal stability of NDI-ID can be enhanced by the intramolecular and intermolecular short contacts,indicating the conformational rigidity dictates the morphological stability of film phase.On the other hand,the dynamic topological transformation of material molecules occurs during the solvation process and,where the intramolecular hydrogen bonds are attenuated by the interactions with the surrounding solvent,leading to the increased solubility.The meta-stable molecular configuration of NDI-ID endows the favorable union of the superior solution processability and higher thermal stability,and the insights are also perfectly exemplified by the newly designed CTMs.Therefore,these results reveal the significant role of structural dynamics on material properties,which can contribute to highly efficient and stable CTMs.In Chapter 3,the charge mobility of electron transporting materials(ETMs)is intimately connected with relative arrangement and stacking morphology of material molecules.Here,we firstly present a concept of multifunctional I-shaped configuration that can construct better face-to-face stackings for all the investigated ETMs.The results show that NDI-PhE appended with cyclic groups can bring forth the relatively decent electron mobility.More importantly,our calculations thoroughly unveil the molecular rationale behind the better transport properties as the introduction of cyclic groups.We illustrate that,with the introduction of cyclic side chains,the unique configuration can achieve the optimal face-to-face stacking that links to the synergetic effect of stronger intermolecular noncovalent interactions and steric hindrance,which is the primary contribution to the better charge transport properties.In addition,the Energy Decomposition Analysis(EDA)unveils that the thermal stability for the investigated molecules can be enhanced mainly because of the dispersion interaction produced between the cyclic groups.Therefore,this unique molecular configuration is expected to simultaneously improve the two key intrinsicproperties of ETMs,which opens a new paradigm for rationally designing the state-of-the-art ETMs in perovskite solar cells.