Surface And Composition Modulation Of Lead Halide Perovskite Nanocrystals And Their Applications In Solar Cells

Lead halide perovskite nanocrystals possess high photoluminescence quantum yield,narrow photoluminescence spectral emission,tunable band gap and simple process of synthesis,making them promising optoelectronic materials that have been widely applied in the next-generation displays,lighting,and solar cells.Perovskite nanocrystal based solar cells have become one of the research hotspots in recent years.The power conversion efficiency(PCE)has been rapidly improved in recent years with the highest certified efficiency exceeding 18%,far higher than that of traditional nanocrystal or quantum dot solar cells.Furthermore,compared to bulk perovskite materials,perovskite nanocrystals offer more opportunities in terms of phase stability,flexible device construction,and large-area device fabrication.However,there is still large gap between the device efficiency compared to solar cells based on bulk perovskite films.This thesis focuses on the surface and component modulation of perovskite nanocrystals,studying the effects of ligand and component selection on the basic optoelectronic properties of solar cells,providing feasible ideas for further improving the efficiency and operational stability of perovskite nanocrystal solar cells.The specific research work is discussed below:1)Targeted design of surface configuration on CsPbI3 perovskite nanocrystals for high-efficiency photovoltaics.The advanced optoelectronic characteristics of lead-halide perovskite nanocrystals have offered new possibilities for the photovoltaic device applications.However,their dynamic ligand binding and fragile crystal structure make conventional nanocrystal surface manipulation strategies inaccessible.It is urgent to specially design the surface configuration of nanocrystals for high-efficiency photovoltaics.Here,we develop the synthesis of CsPbI3 nanocrystals with guanidinium(GA+)-anchored surfaces based on vacancy-suppressed ternary-precursor method.The hydrogen bonding between GA+ and iodine can reinforce the CsPbI3 nanocrystal surfaces and improves surface passivation.In addition,the short-chain GA+ can ensure a high interdot coupling in the nanocrystal films.As a result,the obtained CsPbI3 nanocrystal films can achieve both low trap density and high carrier mobility.Ultimately,a champion PCE of 15.83%can be achieved.In addition,the production yield of the ternary-precursor method is significantly higher than that of the conventional method(Binary-precursor method),which makes the synthesis protocol suitable for future scalable manufacturing.2)Direct synthesis of CsxFA1-xPbI3 perovskite nanocrystals and their photovoltaic device application.Mixed cation perovskite nanocrystals have achieved the reported highest certified efficiency due to their adjustable bandgap and superior phase stability,providing new possibilities for breaking through the efficiency bottleneck of nanocrystal photovoltaic devices.However,the component-tunable mixed cation perovskite nanocrystals are obtained by first synthesizing CsPbI3 and FAPbI3 nanocrystals separately and then by cation exchange,which limits their further scale-up preparation for applications.Herein,we directly synthesize CsxFA1-xPbI3 nanocrystals with tunable components benefiting from the advantages of the developed ternary-precursor synthesis method.The synthesis of nanocrystals in halide rich environment achieves more uniform size distribution and phase purity.In addition,we apply the nanocrystals to solar cell devices and design heterojunction cell device structures,providing new ideas for the synthesis of mixed cationic perovskite nanocrystals and solar cell fabrication.In conclusion,short-chain GA+ ligands are introduced in the synthesis of perovskite nanocrystals based on ternary-precursor method to modulate CsPbI3 nanocrystals surface and investigate their effects on photovoltaic device performance.Further,mixed-cationic perovskite nanocrystals with tunable components are synthesized by changing the ratio of A-site cation salts in the superior ternary-precursor protocol,and the device performance enhancement and structure optimization is also investigated.