Fabrication Of 2D/3D Perovskite Thin Films And Solar Cells Based On Liquid Crystalline Organic Amine Molecules

In recent years,organic-inorganic hybrid perovskites have emerged as one of the most promising next-generation photovoltaic materials due to their excellent properties.Currently,laboratory-based small-area perovskite solar cells（PSCs）have achieved the power conversion efficiency（PCE）of 25.7%,which will gradually exceed the mainstream polycrystalline silicon solar cells.Despite the dramatic PCE breakthrough,the long-term stability of PSCs for outdoor operation over 25 years remains unproven.To improve the stability of PSCs,the two-dimensional（2D）perovskites are developed.Up to now,massive 2D perovskites based on different organic spacer cations have been prepared,which all exhibit excellent stability.However,pure 2D perovskites suffer from the large band-gap,high exciton binding energy,low light absorption coefficient,and low carrier mobility,thus limiting their applications in photovoltaic devices.To this end,the 2D/3D perovskites are developed by introducing large organic spacer cations into 3D perovskite crystal structures.The 2D/3D perovskites combine the good stability of 2D perovskites with the excellent photovoltaic performance of 3D perovskites,thus becoming the research hotspot.However,most of large organic spacer cations applied in 2D perovskites are insulating or only contain oneπ-conjugated group,which are not electrically active and have weak intermolecular interactions,making it difficult to further improve device efficiency and stability.Therefore,exploring for the novel functional organic spacer cations is a great challenge for developing efficient and stable 2D/3D PSCs.For this sake,in this thesis,a new functional organic spacer cation,π-conjugated biphenyl liquid crystal organic amine,is introduced into the 3D perovskite precursor solution to prepare 2D/3D perovskite thin films and corresponding devices.The focus is on the effect of the introduction ofπ-conjugated biphenyl moieties and their alkane chain length on the performance of 2D/3D perovskite thin films and photovoltaic devices.The main contents are as follows:Firstly,2-4-biphenyl ethylamine iodide（BPEAI）with theπ-conjugated biphenyl mesogen is introduced into the Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ perovskite precursor solution to prepare 2D/3D PSCs.Meanwhile,the octylamine iodide（OAI）and phenylethylamine iodide（PEAI）are selected as references to investigate the effect of theπ-conjugated biphenyl mesogen on the properties of 2D/3D perovskite films and photovoltaic performance of PSCs.The results show that the introduction of the three organic spacer cations can all effectively passivate defects and improve the crystallinity quality of the perovskite films.Compared with the OAI and PEAI,BPEAI can induce the crystalline orientation of the perovskite films and improve the carrier transport efficiency due to the presence ofπ-conjugated biphenyl mesogen.Therefore,the efficiency of the 2D/3D perovskite device with BPEAI reaches 20.83%.Simultaneously,the moisture stability of the perovskite films and PSCs with BPEAI is significantly enhanced owing to the strong hydrophobicity ofπ-conjugated biphenyl mesogens.Secondly,threeπ-conjugated biphenyl organic spacer cations with different alkane chain lengths,including 4-aminobiphenyl iodide（BPAI）,4-phenylbenzylamine iodide（PBAI）,and 2-4-biphenyl ethylamine iodide（BPEAI）,are incorporated into the perovskite precursor solution to prepare 2D/3D PSCs.The effects of alkane chain length on the properties of 2D/3D perovskite thin films and device performance are investigated.The results show that theπ-conjugated biphenyl organic spacer cations with the appropriate alkane chain length can take full advantages ofπ-conjugated biphenyl mesogens,thus effectively passivating defects and promoting the crystal growth and preferred orientation of perovskite grains,thereby improving device efficiency and stability.As a consequence,the 2D/3D PSCs with PBAI achieves an efficiency of 21.05%with excellent humidity stability.Our work provides a new strategy for designing novel functionalπ-conjugated organic spacer cations to improve the device efficiency and stability of 2D/3D PSCs.