High Efficiency And Stable Perovskite Solar Cells:Single Crystal Composition Optimization And Interface Tuning

Perovskite solar cells have become the most promising photovoltaic technology in the third generation of solar cells due to their high photoelectric conversion efficiency and low cost.However,there are still many challenges for perovskite solar cells before they go to market.The most important two challenges are how to further improve device efficiency and greatly improve the long-term stability of the device.In order to better study the above two scientific problems,we have carried out research on perovskite film and single crystals from three aspects of component engineering,interface engineering and optical regulation.The final goal is to realize the preparation of high efficiency and stable perovskite solar cells.The main research contents and results are as follows:1.Constructing the platform for measuring and preparing perovskite solar cells.We have constructed a complete set of instalments and equipment for preparing and characterizing perovskite solar cells,and purchased pharmaceutical reagep^ts and instrument consumables related to perovskite solar cells,which laid the foundation for subsequent scientific research.2.Optimizing the preparation craft of perovskite solar cells from the view of composition and interface engineering.We explored and optimized the preparation process of perovskite solar cells.Specifically,from the perspective of interface engineering,we have determined the optimum thickness of the compact layer,the mesoporous layer,and the hole transport layer.Two new crafts for preparing the hole transport layer by using a drop coating method and the compact layer by using ALD method have been developed.From the perspective of composition engineering,MA or FA-based lead halogen perovskites were selected as the main research system,and the solvent engineering method was determined as the main research method,and the device efficiency was successfully achieved to reach more than 17%.3.Studying the effect of solvent aiid excess compposition on the PCE of FA-based perovskite solar cells..Specifically,the study found that the bromide content has an important effect on the film formation of the FA-based perovskite,While the inerease in the bromide content can significantly inhibit its phase transition.In addition,excessive DMSO inhibits the crystallization of bromide,resulting in the formation of?-FAPbI3.On the other hand,excessive FAI also induces the formation of ?-FAPbI3,which in turn reduces device efficiency.Therefore,by the use of(FAPbI₃)_0.85(MAPbBr₃)_0.5 system with 5%excess PbI₂ and controlling the amount of DMSO,we make the average PCE of perovskite solar cells more than 18%as well as the highest efficiency up to 19.9%.On this basis,the introduction of smaller Cesium ions can further improve the phase stability and reproducibility of the FA-based perovskite,and the PCE can exceed 20%.4.Preparing the FA-based perovskite single crystals and studying their long-term stabilities and structures.This thesis successfully prepared a series of high-quality FA-based perovskite single crystals and systematically compared the effects of the FA-based perovskite crystal different cations(FA,MA,and Cs)and halogens(Br,I)on the nucleation and growth,properties and structure,phase stability and long-term stability.We found that the introduction of Cesium and Bromide can effectively inhibit the formation of the ?-FAPbI3 and reduce defects.Besides,the introduction of Cesium improves thermal stability and greatly improves water oxygen stability and light stability.From the crystal structure level,we reveal for the first time the inherent causes of this stability improvement.On the other hand,it has been found that these mixed cations and halides single crystal alloys have intrinsic component segregation.When the Cesium content exceeds 10%or the Bromide content exceeds 15%,two potential phase transitions are induced:when the Cesium content exceeds at 10%,CsPbI₂ is separated;when the Bromide content reaches 15%-33%,three intermediate phases are formed.By the evolution cf the intermediate structure with the change of Bromide content,we have revealed the position of Bromide ion in the crystal structure and the effect of inhibiting the phase transition of the FA-based perovskite from the crystal structure level for the first time,and explained the synergistic effect of the smaller MA and Cs ions on phase stability and the influence of stoichiometric ratio and DMSO content on the crystallinity and phase transition of the FA-based perovskite.Finally,we have optimized the most stable new component of the third generation perovskite-(FAPbI₃)_0.9(MAPbBr₃)_0.05(CsPbBr₃)_0.05.It maintains good structural stability over up to 10,000 h of water oxygen stability and 1,000 h of light stability testing,while it has good thermal stability and long carrier lifetime.We have successfully used this composition to prepare a perovskite solar cell with PCE up to 21%and good stability.5.To further enhance the PCE of perovskite solar cells from the view of optical tuning.This paper attempts to further enhance the PCE of the device from the perspective of optical regulation.Specifically,the plasmon-enhanced perovskite solar cell is realized by introducing the shell-isolated metal nanoparticle.We chose the gold nanorods that is dominated by scattering and adjusted its SPR peak to 700-800 nm(the red light region where the perovskite absorbs weakly).The surface of the particle is wrapped with a certain thickness of the insulator shell to prevent the carrier from recombining on the surface of the metal nanoparticle,and the iodide ion adsorption is inhibited to protect the interface stability of the Perovskite and the nanomaterial.In order to introduce water-soluble nanoparticles onto the surface of perovskites,we have tried various preparation device process.It was finally found that dissolving the nanoparticles in an isopropanol solution and using a stable perovskite component is an effective method.