The Fabrication Of Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cell

Perovskite solar cells(PSCs)have attracted worldwide attentions because of their high power conversion efficiency(PCE),solution processing fabrication technology and low cost.Planar heterojunction PSC(PH-PSC)provides us a new direction for the preparation of highly efficient PSCs without hysteresis.Although the PCE of p-i-n PH-PSC(inverted structure)is slightly lower than that of the n-i-p PH-PSC,its preparation process is simple and the hysteresis effect is weak.Many approaches were tried to improve the PCE of p-i-n PH-PSCs,such as optimizing the device structure and the fabrication process,adopting doping engineering,controlling temperature,interfacial engineering,and controlling the morphology of perovskite layer.In this thesis,highly efficient PSCs were obtained by interfacial modification,modulating the morphology of perovskite layer and optimizing the fabrication process.Some works were carried out as follows:(1)The morphology of the perovskite thin film was optimized via modifying the surface of hole transport layer(HTL)poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)(PEDOT: PSS)with polar solvents,DMSO,ethanol,ethanol:10 vol% DMSO,DMF and acetonitrile.After surface modification with polar solvents,the modified PEDOT: PSS films have the similar morphology and electrical properties.However the morphology of perovskite films deposited on solvent modified PEDOT: PSS were differ from each other.It was found that both the stability of the intermediate phase MAI-DMSO-Pb I2,which is related to the coordination ability of the solvent molecules,and the morphology of PEDOT: PSS film,influenced the morphology of the CH3NH3 Pb I3(MAPb I3)film.MAPb I3 film with a uniform crystal size and smooth surface was obtained when being deposited on top of PEDOT: PSS that has been modified with solvent with a strong coordination ability.In the other cases,crystal size homogeneity and surface roughness of the MAPb I3 film was worse.The improved surface roughness and crystal size homogeneity of the MAPb I3 film enhanced the short circuit current(JSC),and therefore the PCE of PSC.After modifying the surface of PEDOT: PSS with ethanol: 10% DMSO,the JSC of PH-PSC increased from 16.73 m A/cm2 to 20.4 m A/cm2.Hence,the PCE increased from 11.6% to 13.19%.(2)Improving the charge transporting property of the electron transport layer(ETL)fullerene derivative(PCBM)by modifying the surface of PCBM with solvent.After modifying the surface of PCBM with polar solvents ethanol,acetonitrile and ethanol: acetonitrile,respectively,the morphology of PCBM changed and the electron mobility in PCBM increased.A dipole layer was formed at the PCBM/Ag interface because of the polarity of polar solvent,which lowered the energy gap between PCBM and Ag.Therefore,the collection of electrons was improved.The JSC and open circuit voltage(VOC)of PSCs increased.When PCBM was modified with ethanol: 5% acetonitrile,the PCE of PH-PSC increased from 10.5% to 13.31%.(3)Optimizing the morphology of perovskite films by controlling its preparation process.During the spin-coating of perovskite precursor solution,toluene was dripped to improve the crystallization of perovskite.For conventional anti-solvent washing method,anti-solvent was dripped slowly,resulting in dark brown mirror-like perovskite film.In this work,white mirror-like perovskite film was achieved by tuning the angle between the pipette and the substrate,the dripping speed of toluene,and the amount of toluene used.Experimental results showed that the white perovskite film had fewer internal defects,less horizontal grain boundaries,and higher carrier mobility,which improved the JSC of PSC from 18.7 m A/cm2 to 21.66 m A/cm2,and therefore the PCE from 12.5% to 15.4%.