Interfacial,Engineering With Catechol Derivatives And Transition Metal Dichalcogenides For High-Performance Perovskite Solar Cells

Hybrid organic-inorganic perovskite solar cells（Pero-SCs）have attracted plenty of attention due to the merits of high power conversion efficiency（PCE）,solution-processability and low fabrication cost and so on.The certificated PCE of the best Pero-SC is as high as 22.7% so far,which has met the requirements for the commercialization of solar cells.In the future,it is expected to fabricate Pero-SCs modules and flexible Pero-SCs,which is complementary to the current commercial solar cells.The development of new and stable perovskite active layer materials,simple and easy way of fabrication,low-cost and environmentally friendly interface layer materials and preparation of large-area Pero-SCs have been the research focuses in the field.This thesis systematically studied how to prepare a highly efficient and simple structure Pero-SCs,especially focusing on modification or substitution of the traditional interface layer materials via introducing catechol derivatives and 2D transition metal dichalcogenides（TMDs）,aiming at high efficiency and stable Pero-SCs.The details are as follows:1.A series of catechol derivatives,L-3,4-dihydroxyphenylalanine（DOPA）,norepinephrine（NE）and 3,4-dihydroxybenzhydrazide（DOBD）,were employed as dopants in PEDOT:PSS and applied as hole transport layers（HTLs）in p–i–n Pero-SCs.The influence of different catechol doped HTLs on the performance of Pero-SCs was systematically studied.It was found that all these three catechols could improve the PCE of Pero-SCs.The investigations indicated that the PCE improvement should be mainly attributed to the facilitated hole collection and transportation due to the improved conductivity of the doped HTL and the enhanced crystallinity of the perovskite films prepared on the HTL.This line of research demonstrates that the easily accessible catechols can be employed as an excellent dopant in PEDOT:PSS for application as HTLs in Pero-SCs and opens a novel avenue for further improving the performance of the devices.2.In p-i-n Pero-SCs,one of the most commonly used HTL material is PEDOT:PSS.However,its shortcomings of hygroscopicity and the unsuitable energy level are not good for fabricating high performance p-i-n Pero-SCs.All these drawbacks limit its further application in Pero-SCs.Here,a simple method of codoping DOPA and DMSO into PEDOT:PSS as HTL was used to fabricate p-i-n Pero-SCs.The results show that DOPA and DMSO codoped PEDOT: PSS as HTL could effectively adjust the energy level of PEDOT:PSS for matching with perovskite film and improving the conductivity of PEDOT:PSS.In addition,the crystallinity of the perovskite films grown on top of the codoped PEDOT:PSS is improved and its crystal size is enlarged.PCE of the Pero-SCs increased dramatically from 13.35% for the device with the HTL without codoping to 17.54% for the device with the HTL codoped by DOPA and DMSO.3.Two integrated organic-inorganic HTLs composed of 2D MoS₂/PEDOT:PSS and 2D WS₂/PEDOT:PSS were prepared and used in Pero-SCs.It is found that the integrated organic-inorganic HTLs can improve PCE of the Pero-SCs.Moreover,the Pero-SCs with the two integrated organic-inorganic HTLs showed improved stability.The XPS analysis indicates that the introduction of 2D MoS₂ and 2D WS₂ between ITO and PEDOT:PSS can effectively suppress the diffusion of In elements of ITO into PEDOT:PSS,which could lead to the improved stability.4.As alternatives,herein water-soluble 2D Transition metal dichalcogenides（TMDs）,MoS₂ and WS₂,were employed as HTLs in Pero-SCs.It was found that the content of 1T phase in the 2D TMDs HTLs is important to the performance of Pero-SCs,and the 1T-rich TMDs（as achieved from exfoliation and without post-heating）lead to much higher PCEs.More importantly,as PEDOT:PSS was replaced by 2D TMDs,both the PCEs and stability of Pero-SCs were significantly improved.The highest PCEs of 14.35% and 15.00% were obtained for the Pero-SCs with 2D MoS₂ and 2D WS₂ as HTLs,respectively,while for the Pero-SCs with PEDOT:PSS only as HTL showed a PCE of only 12.44%.These are up to date the highest PCEs of the Pero-SCs using 2D TMDs as HTLs.This study demonstrates that water-soluble 2D TMDs have great potential for the application as new generation of HTLs aiming at high performance and long-term stable Pero-SCs.5.A room temperature and aqueous solution-processed 2D TMDs,TiS₂,was applied as an electron transport layer（ETL）in planar n-i-p Pero-SCs.Upon insertion of the 2D TiS₂ ETL with UVO treatment,the PCE of the planar Pero-SCs was optimized to 18.79%.To the best of our knowledge,this value should be the highest efficiency to date among those PCEs of the n-i-p Pero-SCs with room temperature processed metal compound ETLs.More importantly,the n-i-p Pero-SCs with the UVO-treated 2D TiS₂ as ETL also showed high stability,where the average PCE remained over 95% of its initial value after 816 hours storage without encapsulation.6.SnO₂ has been demonstrated as an effective ETL for attaining high-performance Pero-SCs.However,the trap states in SnO₂ will reduce the Pero-SCs performance and results in serious hysteresis.Here,we report a strategy to improve the charge transport ability by inserting an aqueous-processed 2D TiS₂ between SnO₂ and perovskite films.It is found that the device fabricated with 2D TiS₂ modified SnO₂ as ETL could reach a highest power conversion efficiency（PCE）of 21.73%（an average PCE of 20.62 ± 0.46%）with little hysteresis.The improvement of performance mainly resulted from the passivation of the trap states,the improvement of charge transporting and the better match of energy levels between ETL and perovskite.This work offers not only a promising material for interface engineering,but also provides a viable approach to address the challenges of trap states of SnO₂ in planar n-i-p Pero-SCs.