Surface Modification And Electronic Device Of Organic-inorganic Hybrid Perovksite

In recent years,the increasing serious of energy crisis and environmental pollution provoked people looking for clean and renewable energy sources to instead of the conventional fossil energy.Solar energy is one of the most abundant renewable energy sources on earth,which can be conversed to electric energy via photovoltaic technology with the merits of green and environmental-protection.Perovskite solar cells with organic-inorganic hybrid perovskite(ABX3:A= CH3NH3+or CH(NH2)2+,B = Pb2+,X=I-or Br-or Cl-)as an absorber and amazing photon to electron conversion efficiency,is the game changer in photovoltaics.The photoelectric efficiency of perovskite solar cell has been improved remarkably from 3.8%to 22.1%since 2009,which is almost comparable with that of single-crystal Si solar cell.In addition,the perovskite solar cell can be fabricated by simple solution-processed method with low cost.Therefore,perovskite solar cell is expected to be the next generation of pratically used solar cell after Si solar cells,and was endowed as one of the top 10 scientific breakthroughs in 2013.However,the unstability is the key drawback of perovskite solar cell to practical use.Perovskite materials have a low tolerence to the ambient environment,such as moisture,which can induce the decomposion of CH3NH3PbI3 into CH3NH3I and PbI2.The work of this thesis is amied at improving the stability and exploring the new application in other optoelectronic devices of perovskite materials by interface engineering.Hydrophobic functional organic molecules,such as perylene diimide,aniline with different electric properties and aliphatic amine with different length.The details are as following:In Chapter 1,we review briefly the structure and electric properties of organolead halide perovskite,the preparation of nano-perovskite and the recent achievements of interface engineering in solar cell,LED and laser with organolead halide perovskite as the active layer.In Chapter 2,a perylene diimide with cation groups is designed and synthesized as an electron acceptor and 4,4'-Stilbenedicarboxlic acid(SDBA)is chosen to be the electron donor to investigate the effect of photoisomerization of donor on the electron transfer process across the infercace.Both trans-and cis-SDBA molecules can form stable complexes with column PDI-I aggregates in water with a 1:1 stoichiometry via ionic interactions,but the complex of cis-isomer is more stable as revealed by the UV-vis absorption and fluorescence spectroscopy.The electrochemical experiments suggest that cis-SDBA is a better electron donor than its trans-isomer.However,fluorescence quenching experiments suggest that the electron transfer from trans-SDBA is more efficient than that from cis-SDBA,which is obviously contradictory to the results of binding constant and the electrochemical experiments.The contradictory results can be attributed to that the columnar aggregates(PDI-I)n are utterly destroyed in cis-SDBA-(PDI-I)n system caused by stronger ionic interaction between cis-SDBA and(PDI-I)n.Also the bending conformation of cis-SDBA probably results in a larger distance between cis-SDBA and the surface of(PDI-I)n.The results of this research provide a guide for the aggregation behavior of perylene diimide to modify organolead halide perovskite.In Chapter 3,an organic dye modified organolead halide CH3NH3PbBr3 nanoparticle(cubic)is prepared successfully by using a perylenetetracarboxylic diimide(PDI)bearing an-NH3+ head group as the capping ligand.XRD and HRTEM reveal that the nanopartilces are homogenous with high crystallinity.The photoluminescence of perovskite is quenched completely by the chemically adsorbed PDI molecules.The steady and transient photoluminescence spetra suggest the presence of efficient fluorescence quenching,which confirms that the PDI molecules are anchored on the surface of CH3NH3PbBr3 nanoparticle.The resulted nanoparticles can be dispersed in organic solvents and the resulted dispersion keeps stable for days.This result provides a general guideline for surface engineering of organolead halide CH3NH3PbBr3 nanoparticle.In Chapter 4,chemically decorating CH3NH3PbBr3 with a group of para-substituted arylamine(R-An)was investigated,where R ranges from electron-withdrawing trifluoromethoxy(-CF3O),to hydrogen or electron-donating ethoxy(-EtO).Different ratios ofR-An ammonium bromide and methylammonium bromide(MA)(R-An/MA = 3/7,4/6,5/5,6/4 and 7/3)were tested.XRD patterns revealed that the perovskite nanocomposite were cubic with good crystallinity.TEM and photoluminescence suggested that the perovskite nanocrystals were composed of 2D layered and 3D bulk structures.1H NMR and TGA experiments revealed that the non-substituted aniline can readily adsorb to the surface of perovskite at any ratios between R-An and MA.But an EtOAn/MA ratio ? 1 is needed to anchor the EOAn molecules on the surface of perovskite.For the arylamine with the electron-withdrawing-CF3O group,it cannot adsorb to the surface of the perovskite at any concentrations.This result reveals that both steric hindrance and alkalinity can affect the anchoring of arylamine on the surface of CH3NH3PbBr3 perovskite.I-V curves of the perovskite nanocrystal films prepared by spin coating suggest that proper surface modification can increase the conductivity significantly.The result opens a new way to tunethe properties of organolead halide perovskite.In Chapter 5,we have explored for the first time the application of organic-inorganic hybrid perovskite as gas sensor for the toxic NO2 based on an electron-transfer process accross the interface.Four spin-coating films(SCFs)from different concentration(20,25,30 and 35 wt%)of precursor solution and perovskite nanoparticle film(NPF)are used to fabricate N02 sensor.The results revealed that all the sensors exhibted fast and reversible response to N02.The detection limit follows the order of NPF(0.1 ppm)= 35 wt%(0.1 ppm)>30 wt%(0.15 ppm)>25 wt%(0.38 ppm)= 20 wt%(0.38 ppm).Morevover;?I/I0 of sensors is in order of NPF>30 wt%>35 wt%>25 wt%>20 wt%according to current changes of the sensors as function of NO2 concentration.So NPF has the best sensing performance.The sensing mechanism of perovskite film is proposed.The toxic NO2 gas can be adsorbed on the surface of CH3NH3PbBr3 film physically when the sensor is exposed to NO2,and then NO2(ad)will be formed.Then NO2(ad)can extract electron from the conduction band of perovskite due to the strong electron-withdrawing property of NO2.As a result,the density of electron decreases,so the electronic condutivity will be reduced.This organolead halide perovskite based chemical sensors are very promising due to the merits of low detection limit and fast response at room temperature,as well as low-cost and easy fabrication.In Chapter 6,aliphatic ammonium with different length(8,12 and 16 carbon)linear chain was used to modify spin-coating CH3NH3PbBr3 films by immersion method.A hydrophobic molecular layer can be formed on the surface of perovskite for moisture-protection to improve the stability of perovskite film.After modification,the fluorescence lifetimes were significnalty prolonged as revealed by the transient photoluminescence experiments,which can be ascribed to the passivation of the perovskite surface.The formation of hydrophobic layer on the surface of perovskite materials was also supported by the contact angle of water,which increased from 38.1° for the film before modification to 103.9° after the modification.The optimized condition for modification is 20 mM for 1.5 h in dodecylammonium bromide.The stability of peorvskite film is significantly improved.