Modification Of Functional Layer Interface And Its Effects On The Performance Of Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells(PSCs),as a typical class of the third generation solar cells,have gone through rapid development with the advantages of high conversion efficiency and low costs.Because of the stacked structure,there are many interfaces between the functional layers in the PSCs.Among these,interfaces between the transporting materials and the photoactive layer play a critical role in controlling the behavior of charge carriers and the crystal quality of the adjacent functional layers.Given the importance of interface between transporting materials and the photoactive layer as explained above,this work focuses on the research of interface engineering between transporting materials and perovskite.It aims to explore various kinds of engineering strategies to achieve the energy level alignment,the charge extraction and transportation improvement,recombination losses reduction,and the perovskite film crystal quality optimization.The main results are summarized as follows:(1)A facile one-step,in situ and low-temperature methods was developed to prepare an Nb:Ti O₂ compact-mesoporous layer which served as both scaffold and electron transport layer(ETL)for PSCs.Titanium oxide(Ti O₂)has been commonly used as an electron transport layer.However,existing fabrication approaches for mesoporous Ti O₂generally require a high temperature annealing process(>450°C).The Ti O₂layer usually suffer from low electron mobility and poor conductivity.In this work,the Nb:Ti O₂layer was prepared by the reaction of Nb Cl₅ ethanol solution and Ti Cl₄ aqueous solution at a low temperature of 70°C.It contains a compact Ti O₂ bottom with nano-pin morphology on the surface,which can be utilized as scaffold.The hysteresis index decreased significantly from 24.39%for the PSC based on bare Ti O₂ to 3.19%for that based on 2%Nb:Ti O₂ layer.Such improvement is due to the collaborative effect of the direct carrier transportation route created by the nano-pin morphology and the improved carrier transportation rate because of the presence of Nb.Compared to lower PCE(15.70%)obtained from the device with bare compact Ti O₂ layer,the high-quality Nb:Ti O₂ layer allowed the PSCs to achieve remarkable PCE of 19.74%.(2)Ti₃C₂T_x(a typical MXene material)was incorporated as an interface modification layer between the SnO₂ ETL and the perovskite absorber layer of perovskite solar cells.SnO₂ is a highly efficient ETL used in planar PSCs because of its high mobility,suitable CBM,high transparency,and low temperature processing character.Here,the Ti₃C₂T_xwas deposited on SnO₂ to further improve the surface wettability through the interaction of surface termination of Ti₃C₂T_x and CH₃CH₂I.It is found that the addition of MXene could contribute to an increase of adsoption sites for nucleation,eventually modify the film formation and crystal growth of perovskite.SEM results showed that the average grain size of the perovskite increased from 0.46 to 1.16?m after the introduction of Ti₃C₂T_xcompared with the pristine sample,and the power conversion efficiency was improved from 15.78%to 19.39%.(3)The PSCs were modified by introducing argon plasma post-treatment on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS).PEDOT:PSS is one of the most common HTL used in the configuration,due to its excellent optical transparency,flexibility and hydrophilic nature.But its inferior electron transportation capability induced by PSS component is the main reason of low performance in the inverted PSCs.In this work,a simple and effective method of argon plasma post-treatment on PEDOT:PSS was proposed to improve the performance of perovskite solar cells.XPS results showed that the excess PSS was easily removed away from the surface of the PEDOT:PSS by plasma,leading to the enhancement of hole extraction and transportation.It is found that the ratio of PEDOT to PSS was increased from 14%to44%,and the electronic conductivity was increased from 12.8 m S cm^-1 to 17.9 m S cm^-1.Furthermore,both the wettability of perovskite and PEDOT:PSS and crystal growth quality were improved by the dangling bonds brought from argon plasma.We believe this strategy of affecting the composite on the polymer surface and carrier transportation using plasma can inspire further innovative designs of PSCs.(4)The one-step deposition procedure is a fast and simple fabrication method to prepare perovskite film.However,the perovskite film usually exhibits Branch-like morphology with low surface coverage.There has been reported that the dissolution-recrystallization method(DRM)with chlorobenzene is an effective strategy to control perovskite crystallization.However,the solvents such as chlorobenzene are poisonous and environmental-unfriendly.Herein,a novel and facile inactive gas assisted method is introduced to prepare perovskite film during the one-step solution deposition process.The dried gas blows over the surface of the perovskite solution during the spin-coating process,which promote a faster solvent evaporation.Then,the uniform and compact perovskite film on the substrate was achieved.Combining the solvent engineering of DMSO and such air-assistance technique,perovskite layer can remain uniform and dense morphology with grain size over 1?m no matter when the air flow was added.This work lay the foundation for fabricating the highly efficient and repeatable PSCs.