Design And Synthesis Of New Interfacial Material For Perovskite Solar Cells

In recent years,the power conversion efficiency?PCE?of perovskite solar cells?PSCs?has soared from the initial 3.8%to the current 25.2%,and has attracted widespread attention from scientific researchers.In perovskite solar cell,the light absorbing layer is located between hole-transporting layer?HTL?and electron-transporting layer?ETL?.Under solar illumination,the diffusion length of charge carriers generated by the perovskite layer is generally in the order of micrometers.The transmission loss within the perovskite layer is very low.Most of the losses are due to carrier recombination at the perovskite/electron-transporting materials?ETM?and perovskite/hole-transporting materials?HTM?interfacial.The existence of a large number of trap states on the surface and grain boundaries of perovskite is one of the reasons for carrier recombination.Therefore,an effective method is needed to passivate the trap state to reduce the carrier recombination at the surface and grain boundaries of the perovskite film,thereby obtaining a high-efficiency device.There are three main methods reported:1)adding additives to the perovskite layer;2)introducing interfacial material between the perovskite layer and the charge-transporting layer for interface modification;3)introducing a group that can passivate the defect state to charge-transporting material.In this thesis,we conduct research based on the latter two methods:designed and synthesized a series of interfacial material based on tetraphenylethylene-diketopyrrolopyrrole and introduced them between the perovskite layer and the electron-transporting layer;in addition,we have introduced groups with electron-withdrawing ability into carbazole-based hole-transporting materials,which not only can extract and transport holes,but also passivate trap states at the surface and grain boundaries of the perovskite.The main content of this thesis includes the following two aspects:1.A series of tetraphenylethylene-diketopyrrolopyrrole?TPE-DPP?derivatives with different alkyl chain lengths were designed and synthesized,and used as interfacial material in inverted perovskite solar cells.The effects of alkyl chain lengths on the electronic property of these compounds and the performance of perovskite solar cells?PSCs?were investigated.Cyclic voltammetry?CV?results show that the effects of different alkyl chain lengths on the molecular energy levels of these TPE-DPP derivatives can be ignored.Atomic Force Microscopy?AFM?images show that the surface of the perovskite film deposited with the TPE-DPPC12 interfacial material is the smoothest,ensuring a good interfacial contact between the perovskite layer and the C₆₀electron-transporting layer.Steady-state fluorescence?PL?spectroscopy shows that the TPE-DPPC12 interfacial material can effectively extract the electrons generated by the perovskite layer.The J-V curve test results show that the average power conversion efficiency of the device introduced with the TPE-DPPC12 interfacial material is 18.37%,which is 17%higher than the C₆₀-based reference device?16.37%?.In addition,TPE-DPPC12 has good hydrophobicity,and the introduction of TPE-DPPC12 interfacial material is beneficial to improve the environmental stability of inverted PSCs.The research in this chapter shows that the alkyl chain length of the TPE-DPP interfacial material does not affect the energy level of the molecule,but has a significant effect on the surface morphology of the film and the electron extraction ability of the molecule,thereby affecting the performance of the PSCs.2.Three carbazole derivatives KZ,KZIC and KZRD were designed and synthesized.Compared with KZ,KZIC and KZRD introduced electron-withdrawing groups3-?dicyanomethylene?indone?IC?and 3-ethyl rhodanine?RD?on the end groups,respectively,forming an asymmetric D-A?Donor-Acceptor?structure.These three molecules were used as hole-transporting materials in perovskite solar cells,and the effect of molecular design of asymmetric structure on the hole-transporting properties of the material was studied.AFM images show that the surface of the perovskite film with KZRD deposited is the smoothest,ensuring good interfacial contact between the perovskite layer and the metal electrode.The hole mobility and steady-state PL decay curve show that KZRD has the best hole extraction and transport ability.The results of the J-V curve test show that the PSCs with KZRD as the hole-transporting materials have the best performance,and achieved an power conversion efficiency of 19.07%.Under the same conditions,the power conversion efficiency of PSCs based on KZ and KZIC is16.05%and 18.04%,respectively.Studies have shown that the introduction of an electron-withdrawing group to form an asymmetric D-A structure enhances the interaction between molecules and improves the hole extraction and transport ability.