Enhanced Efficiency And Stability For Perovskite Solar Cells Via Antisolvent And Interfacial Modification

With the increasingly serious energy crisis and environmental pollution,developing new energy is imminent.Since the sunlight is an inexhaustible and clean energy,developing solar cells to convert the sunlight into electricity is one of effective ways to solve the global energy crisis and environmental pollution.In recent years,organic-inorganic hybrid perovskite solar cells?PSCs?have been widely investigated due to their rapid develop in power conversion efficiency?PCE?.The perovskite materials have many excellent optoelectronic properties such as high carrier mobility,long carrier diffusion length,high extinction coefficient,high defect tolerance and tunable band gap.Now,the highest recorded PCE for the PSCs has reached up to 23.7%,showing great commercial application prospect.Though,much progress have been made for the PSCs,there are still many factors limiting the further enhancement for the device performance such as the carrier transport at the electron transport layer?ETL?/perovskite or perovskite/hole transport layer?HTM?,the polycrystalline of the perovskite,the ion migration in the perovskite film and so on.In this paper,we main studied the optoelectronic performance of the planar heterojunction PSCs from the interface engineering,the passivation of perovskite active layer and the preparation of high-quality perovskite films.The main contents of this paper are as follow:?1?Introducing SnO₂ modification layer at TiO₂/perovskite interface.SnO₂ layer is introduced at the TiO₂/perovskite interface by a simple solution spin coating method.After the optimization of the devices,we find that the optimal annealing temperature of the SnCl₂ is 180 ^oC.When the annealing temperature is low,the SnCl₂can't form SnO₂,acting as an insulating layer to prevent electron transport.However,when the annealing temperature is high,the open-circuit voltage(V_oc)and fill factor?FF?of the devices will decrease,leading to the decrease of the device performance.After selecting the optimal annealing temperature,we investigated the effect of concentration of the SnCl₂ ethanol solution on the device performance.The optimal concentration of SnCl₂ ethanol solution is 0.05 M.The SnO₂ layer prepared with high concentration of SnCl₂ ethanol solution can significantly reduce the short-circuit current density(J_sc)and FF of the device.Finally,compared with the TiO₂ based device,the introduced SnO₂ modification layer can improve the J_sc,V_oc and FF significantly.And the J_sc,V_oc,FF and PCE for the best devices are 20.8 mA cm^-2,1.08V,0.75 and 16.8%,respectively,which show an enhancement of 28%compared with that?13.1%?of the control device.In addition,the steady-state output power is 15.1%.According to the scan electron microscope?SEM?,atomic force microscope?AFM?,the introduced SnO₂ layer has almost no effect on the grain size and the surface roughness of the MAPbI₃ film.Finally,by the steady-state fluorescence?PL?,transient fluorescence?TRPL?,electrochemical impedance?EIS?,and space charged limited current?SCLC?test,the introduced SnO₂ can effectively passivate the surface defects of the TiO₂,improve the electron extraction at TiO₂/perovskite interface and finally suppress the carrier recombination at TiO₂/perovskite interface,which are the main reasons for enhanced device performance.?2?Introducing a novel fullerene derivative(C₆₀?QM?₂)into MAPbI₃ films by anti-solvent dripping.First,we investigated the effect of the concentration of C₆₀?QM?₂ in chlorobenzene on the device performance,when the concentration of the C₆₀?QM?₂ is 0.4 mg/mL,the optimal device performance can be obtained.The higher PCE for the optimal device is 18.4%with the steady-state output power of 17.93%,which shows 10%enhancement in comparison with that?16.7%?of the control device.In addition,the hysteresis for the MAPbI₃:C₆₀?QM?₂ based device is suppressed effectively.By SEM,XRD and AFM characterization,it indicates that the introduced C₆₀?QM?₂ mainly exists on the surface and at the grain boundary partly of the MAPbI₃ film.The C₆₀?QM?₂ doesn't change the crystalline and grain size of the MAPbI₃ film,but reduce the surface roughness of MAPbI₃ film,which improves the MAPbI₃/Spiro-OMeTAD interface and reduces the interfacial contact resistance.According to the results of the PL,TRPL,EIS and SCLC test,the introduced C₆₀?QM?₂ can effectively passivate the defects on the surface and grain boundaries of the MAPbI3 film,which inhibits the carrier recombination in MAPbI3 film and enhances the hole extraction at MAPbI3/Spiro-OMeTAD interface.In addition,the introduced C₆₀?QM?₂ also can make the electron and hole transport more balanced in the devices.Finally,the introduced C₆₀?QM?₂ can significantly enhance the surface hydrophobicity of MAPbI₃ film,which can effectively prevent the infiltration of moisture in the air into the perovskite active layer,and delay the decomposition of the MAPbI₃ film.Therefore,the air stability of the device is also significantly improved.?3?Preparing high-quality MAPbI₃ film by using chlorobenzene/acetonitrile?ACN?anti-solvent.When the ACN additive is introduced,the quality of the MAPbI₃film is improved.With the proportion of the ACN additive increase,the grain size of the MAPbI₃ increase,however,further increasing the amount of ACN,the grain size of the MAPbI₃ begins to decrease.The optimal proportion of the ACN is 6%volume of the chlorobenzene,and the MAPbI₃ film with maximum grain size and uniform distribution can be obtained.At the same time,the intensity of the UV-vis spectrum absorption for the MAPbI₃ is also enhanced.By fourier infrared test,we found that the ACN additive could control the mount of DMSO in the intermediate phase CH3NH₃I-PbI₂-DMSO,the more the amount of acetonitrile additive is,the less DMSO residue will be.The excess DMSO will lead to the small grain size and inhomogeneous distribution of the MAPbI₃ film due to the slow evaporation of DMSO,while too little DMSO residue can make MAPbI₃ rapid crystallization,which is not conducive to preparing MAPbI₃ film with large grain size.Thus,by tuning the ACN,the amount of DMSO in the intermediate phase of perovskite can be effectively regulated,so as to prepare high-quality MAPbI₃ films with large grain size.Finally,the Jsc,Voc,FF and PCE of the optimal device prepared based on chlorobenzene/acetonitrile anti-solvent?volume ratio 1:0.06?were 22.3 mA cm^-2,1.13V,0.75 and 18.9%,respectively.The steady-state output power of the device reaches18.02%,and the PCE of the device was improved by 16.7%compared with that?16.2%?of the reference device.At the same time,the hysteresis of the optimized device is significantly suppressed with the hysteresis index decrease from 0.15 to 0.09,and the stability of the device is also improved to some extent.By PL,TRPL,EIS,SCLC test,it shows that on one hand,the introduced ACN additive can reduce the trap denstity within the MAPbI₃ film,and reduce the nonradiative recombination of carriers,on the other hand,it improves MAPbI₃/Spiro-OMeTAD?SnO₂?contact interface,and reduces the series resistance of the device,which improves the carrier transport in perovskite device.All these factors lead to the enhancement of the device performance and air stability.