Research On Performance Improvement Of Quasi-two Dimensional Perovskite Solar Cells Assisted By Second Spacer Cation

The emergence of quasi-two-dimensional（Q-2D）perovskites has improved the air stability of perovskite solar cells（PSCs）.However,the introduction of an insulating interlayer of cations severely hinders the transport of charge carriers,reducing the power conversion efficiency（PCE）of Q-2D PSCs.Optimizing the crystal orientation and phase distribution of Q-2D perovskites is an effective way to improve device performance.In this work,iso-butylamine（iso-BA）and 3-fluorophenethylamine（F-PEA）were used as second spacer cations to achieve high-quality films and crystal orientation,and thus to prepare highly efficient and stable Q-2D PSCs.The specific research contents of this thesis are as follows:（1）First,the influence of different n values on the Q-2D perovskite film and its photovoltaic performance based on pure iso-BA spacer cations was studied on a PTAA substrate.When n≥4,the film surface was flat,dense and without pinholes,and exhibited a crystal orientation perpendicular to the substrate.Especially when n=4,the crystal orientation was almost completely perpendicular to the substrate,which is conducive to efficient carrier transport.In addition,it was found experimentally that when the PC₆₁BM electron transport layer was spin-coated（using chlorobenzene solvent）,it would damage the underlying Q-2D perovskite film,because the chlorobenzene penetrated the perovskite film and dissolved the PTAA hole transport layer.Although this problem can be solved by replacing PTAA with a PEDOT:PSS substrate that is not soluble in chlorobenzene.The PEDOT:PSS substrate will have adverse effects on charge transport and crystallization.However,when preparing Q-2D perovskite films with n≥5 on a PTAA substrate,due to the large amount of large-n phase produced,the film can effectively block the penetration of chlorobenzene.Therefore,Q-2D PSCs with n=5prepared on a PTAA substrate achieved a higher PCE（15.57%）.（2）In order to make use of the perfect crystal orientation of iso-BA Q-2D perovskite film（n=4）,it is necessary to solve the problem of dissolving PTAA substrate during the spinning process of PC₆₁BM.We found that the iso-BA perovskite film prepared on PTAA has large residual stress.By introducing F-PEA spacer cation to partially replace iso-BA,the residual stress in perovskite can be effectively reduced,thus preventing chlorobenzene from penetrating the perovskite film and dissolving PTAA substrate.At the same time,the introduction of the second spacer cation of F-PEA significantly increased the large-n phase in the perovskite film,forming a uniform n phase distribution.The exciton generated by the small-n phase is transferred to the adjacent large-n phase by energy transfer,and then the photogenerated carrier is output to the corresponding electrode through the charge transfer channel formed by the large-n phase,which greatly improves the exciton dissociation efficiency and carrier transport efficiency.Finally,Q-2D PSCs based on iso-BA&F-PEA second spacer cation obtained 17.17%PCE,which is at a high level in the efficiency of low-dimensional（n≤4）RP-type Q-2D PSCs reported at present.Thanks to the release of film stress and the optimization of n phase,the stability of the device has also been improved.