The Research Of Optical Properties And Applications Of Layered Organic-inorganic Hybrid Perovskite Materials

The enviornmetnal insability of 3D hybrid perovskites has been demonstrated by lots of works.The water vapor,light illustration,heating and other factors can cause its degradation.To improve the stability of the hybrid perovskites,in 2014,Karunadasa et al firstly prepared active materials using layered perovskite PEA₂MA₂Pb₃I₁₀ which with high stability（52%RH,40 days）.The introduction of the large-size organic cations will form a quantum-well structure with the inorganic octahedral layers;for this reason,the layered perovskite materials possess a stronger dielectric confinement effect than its 3D counterpart.From the perspective of structure,the layered perovskites are not suitable for the preparation of solar cells,but this is not the case.The power conversation efficiency of the solar cell using layered hybrid perovskite as photoactive-layer has reached 19.06%,indicating that the layered hybrid perovskite materials have greater application potential.In this work,using optical spectroscopy,the layered PEA₂MA_n-1Pb_nI_3n+1 and 3D MAPb I₃,as model materials,are used to investigate why the quasi-two-dimensional perovskite materials are suitable for solar cells.Meanwhile,a mass of spacer cations and diversified fabrication methods can be used to synthesize the layered hybrid perovskites which are greatly increases the trial-and-error cost of device preparation.To solve this problem,in this paper,the relationship between the physical properties of the perovskite films and the performances of the corresponding devices are also tried to established,hopping that the performances of the corresponding devices can be quickly predicted through the characterization of the perovskite films.Moreover,in the Dion-Jacobson（DJ）perovskites,the large-size organic cations with amine groups at both ends interact with the inorganic layer through hydrogen bonding,resulting in higher structural stability than Ruddlesden-Popper（RP）perovskite in principle.However,in this work DJ-type layered perovskite（PDMA）MAPb₂I₇film become colorless swiftly after being exposed to ambinent condition.Therefore,the macroscopic changes and microscopic mechanisms of this specific DJ-type perovskite film at combient condition were also studed,concluding that hydration is the main reason for such transtion.From the water instability of（PDMA）MAPb₂I₇,（PDMA）MA₃Pb₄I₁₃ was considered to be easily interacting with water too.Therefore,（PDMA）MA₃Pb₄I₁₃ would be used to investigate the interaction between water and layered perovskite,as well as the effect of water vapor on corresponding device performances.So,this paper also works on the effects of water as an additive in preparing（PDMA）MA₃Pb₄I₁₃ films and devices.In this paper,using mainly self-built measurement systems,the optical properties of typical RP-type and DJ-type layered hybrid perovskite materials have been investigated;Furthermore,corresponding perovskite solar cells were fabricated,under the systmetically studies using various fabrication methods and water additives.The research results of this paper can be refined into the following four parts:（1）The optical properties of the laryered RP-type perovskite film PEA₂MA_n-1Pb_nI_3n+1（n=1 abbreviated as PEPI,n=3 abbreviated as PMPI₃,PEA:phenethylamine,MA:methylamine）were studied by absorption and luminescence spectra.In PEPI,the coupling of excitons and optical phonons plays a dominating role in the photophysical process.The absorption spectrum of PMPI₃ film has the characteristics of excitons that from different n-value perovskite phases and the couple of excitons and phonons（average energy～30 me V and 3 times higher than that of PEPI）.At 80 K the behavior of PMPI₃ is similar to that of PEPI,but it is similar to 3D when the temperature is close to room temperature.（2）By using a hot spin coating method,the PMPI₃ film and the PMPI₃ solar cells were prepared at the spinning speeds of 1000r,2000r,4000r and 6000r.The sample prepared at 4000r has the best overall performance and the hysteresis of the 4000r device is smaller than that of the 1000r and 2000r devices.The sample prepared at 6000r has the worst performance,howver,morphological characterization and optical measurement at room temperature cannot explain its bad performance;one reason can be the existence of carrier trapping states that result in thermally activated PL below 200 K（activation energy is 18 me V）,which is absent in 1000r,2000r,and 4000r films.The results suggest that to evaluate the performance of devices,low temperature PL would be necessary.（3）The effect of water vapor and heating on DJ-type perovskite（PDMA）（MA）Pb₂I₇（PDMA:p-Xylenediamine）was studied,it has high robust and rapidly recover thermochromic property.The water moleculars absorption and desorption cause the change of the band gap of（PDMA）（MA）Pb₂I_7,significantly.At room temperature and temperature is higher than 60℃,the film’s band gap is observed to change from 700 nm to 430 nm.The experimental results show that（PDMA）（MA）Pb₂I₇ film as the active material of smart windows which can reduce air temperature in a confined space;it can also be used as the photoactive layer of thermochromic solar cells,its PCE is greater than 0.5%when device under high ambient temperature.（4）The reported results generally show that the DJ-type is more stable than the RP type,but the effects of water as an additive and moisture on the performance of DJ-type perovskite device are poorly understood.Therefore,studying of the effects of water additive and moisture on the performance of DJ-type perovskite（PDMA）MA₃Pb₄I₁₃ solar cells would be useful.The results show that the water additive has little effect on the PCE values of the perovskite solar cells,but it can enhance device’s humidity stability.Being exposed to water vapor from 1 to 9hours gradually,the device’s PCE value firstly increases,and then decreases.The device was prepared with 10%water additive with exposition to air for 2 hours（～65%RH）has the highest PCE（8.18%）.The J_ac is the main affecting factor on device’s perfromance.