| In recent years,perovskite solar cells have been rapidly developed due to their huge commercial potential.At present,the photoelectric conversion efficiency of perovskite solar cells has exceeded25.7%,and its efficiency is close to that of commercial silicon solar cells.However,perovskite solar cells need to be further improved in terms of preparation cost,stability and large-scale production.Studies have shown that electron transport layer materials play a vital role in perovskite solar cells,which can not only improve carrier transport in perovskite absorbing layer,but also help improve the efficiency and stability of devices.The most commonly used electron transport layer materials in trans perovskite solar cells are fullerenes and their derivatives,but they have the disadvantages of high cost,difficult modification and low absorbance,so researchers have shifted their attention to non-fullerene materials（such as naphthimides,perylimides and other small polymer molecules）,which have low cost,easy structure modification,high absorbance coefficient,and have great development potential.In this paper,a series of new naphthimide small molecule materials are designed and synthesized as electron transport layers to prepare low-cost,simple,efficient and stable perovskite solar cells by designing and synthesizing a series of new naphthimide small molecule materials as electron transport layers.The work content is mainly divided into the following two parts:（1）Synthesis and characterization of naphthimide-based electron transport materialsThree n-type semiconductor materials NDIN-CH3,NDIN-2CH3 and NDIN-3CH3 based on naphthimide were designed and synthesized by introducing different nitrogen-containing alkyl chains at both ends.Through thermogravimetric analysis,UV-Vis absorption,X-ray diffraction and cyclic voltammetry,the physical,optical and electrochemical properties of the synthesized small molecule materials were characterized,and the relevant parameters were calculated.The results show that the three small molecules synthesized show good solubility and high thermal stability（the decomposition temperature is much greater than the annealing temperature in device preparation）.The HOMO and LUMO energy levels of NDIN-CH3 and NDIN-2CH3 molecules match the energy levels of the perovskite layer,and the LUMO energy level（-3.30 e V）of NDIN-3CH3 does not match with perovskite,which hinders the transport of electrons to a certain extent.With naphthimide as the matrix,three new naphthimide small molecules NDIN-2S,NDIPh-2S and NDIN-CN were designed and synthesized by introducing thiophene groups into the side chain by bromination reaction and stille coupling reaction.By characterizing their physical,optical and electrochemical properties and calculating the relevant parameters,it is proved that the three n-type semiconductor materials synthesized have certain solubility（NDIPh-2S has relatively poor solubility）and good thermal stability.However,the NDIN-2S energy level（-3.12 e V）does not match the LUMO level（-3.8 e V）of perovskite and its HOMO energy level is shallow,which cannot effectively transport electrons and block the transfer of holes to the cathode.The energy level of NDIPh-2S closely matches the perovskite energy level.（2）Application of naphthimide-based monolayer electron transport layer materials in perovskite solar cellsThe synthesized small molecule materials NDIN-CH3,NDIN-2CH3,NDIN-3CH3,NDIN-2S,NDIPh-2S,NDIN-CN were applied as monolayer electron transport layers to trans-planar perovskite solar cells with ITO/Ni Ox/MAPb Clx I3-x/ETL/Ag structure,and optimized.The results show that NDIN-CH3,NDIN-2CH3 and NDIN-3CH3 achieve photoelectric conversion efficiencies of 6.14%,9.68%and 6.14%,respectively.DIN-2S,NDIPh-2S,NDIN-CN received 12.12%,7.95%,and 8.11%,respectively.In addition,NDIN-CH3,NDIN-2CH3,NDIN-3CH3 and NDIN-2S,NDIPh-2S,NDIN-CN and C60/BCP are used as electron transport layers,and the device efficiency is 10.01%,10.40%,9.41%,14.12%,9.97%,and 11.12%,respectively. |
