Design,Synthesis And Application Of Dopant-Free Hole Transport Materials In Perovskite Solar Cells

Since Kojima et al.firstly utilized the perovskite crystal structure of CH3NH3PbX3 as a sensitizer for dye-sensitized solar cells(DSSC)in 2009,it has led to a remarkably rapid development of perovskite solar cells(pero-SC).With the development for over a decade,the light conversion efficiency of perovskite solar cells,which has been impacted by its continuously optimization structure,has been boosted continuously.To date,the perovskite hole transport layer material is often selected from the traditional material,Spiro-OMeTAD.However,it is necessary to add dopants in the process of battery preparation to make up for its defects of low conductivity.The results show that the addition of dopants will affect the stability of the battery and increase the production cost,prohibiting the commercialization of pero-SC.Therefore,it is significant to design and develop a cheap,efficient and stable dopant-free hole transport material to replace Spiro-OMeTAD for the commercialization of the batteries.Organic small molecular materials have attracted increasing research for optimizing pero-SC performance due to its unique molecular structure,molecular energy level and solubility tunability.Therefore,this work designed a novel hole transport material based on the research of dopant-free hole transport materials,to prepare pero-SC by molecular engineering,and tested the properties of the material.In the first part,a novel phenanthrenone-based hole transport material(Spiro-PT-OMeTAD)was obtained by inserting a carbonyl group into the spirobifluorene framework in Spiro-OMeTAD.The results showed that this small change in structure led to a big difference in their absorption behaviors,frontier molecular orbital energy levels and hole mobilities.The steady-state photoluminescence characterization and the space-charge-limited-current measurement indicated that this phenanthrenone-based material could play an important role in hole collection and transportation in perovskite solar cells.Furthermore,the dopant-free perovskite solar cells based on Spiro-PT-OMeTAD showed highly improved performance by exhibiting a short-circuit current density of 22.36 mA/cm2,an open-circuit voltage of 0.99 V,and a fill factor of 0.62%under 1 sun illumination,which resulted in an overall power conversion efficiency(PCE)of 13.83%,compared to 10.5%for the Spiro-OMeTAD based devices.In the second part,a novel hole transporting material(DBC-OMeTAD)with dibenzopyrene(DBC)as a core was designed and synthesized to change the bonding mode of tetraphenylethylene skeleton,which was inspired by the design of KR216.The molecular structure was characterized by 1H NMR and macromolecular mass spectrometry,and the photophysical,electrochemical,thermal stability,hole mobility and film forming properties of the materials were also studied.In order to investigate the effects of two types of hole transport materials on device performance in various aspects,they were both used to prepare the dopant-free perovskite solar cells and the comprehensive performance of the cells were characterized.The material exhibited excellent film formation measured by atomic force microscopy(AFM).The material showed high hole mobility(5.38X10-4 cm2·v-1·S-1)and power conversion efficiency of 13.12%through testing the device efficiency of material-based single-hole and perovskite solar cells in the simulating sunlight in dark conditions.As a new type of dopant-free hole transport material,DBC-OMeTAD materials exhibited superior performance comparing to KR216.