Controllable Synthesis And Properties Research Of Ag-Based NIR-? QDs Via Energy Band Engineering

Quantum dots(QDs)are a kind of inorganic semiconductor nanomaterial with quantum size effect,which is widely used in solar cell materials,light-emitting diodes,photodetectors,biomedical and other fields.Second near-infrared(NIR-?,1000-1700 nm)quantum dots have been attracted extensive attention from scientific researchers due to their unique wide absorption spectrum,covering the entire solar light region,are ideal solar cell materials.Among them,the silver-based NIR-? QDs are a class of environmentally friendly narrow-band gap semiconductor nanocrystals,the absorption spectrum can be up to about 1300 nm.The studies have shown that the absorption spectrum range of semiconductor nanomaterials can be expanded by precisely regulating the energy band of semiconductor nanomaterials,which is one of the important means to develop new quantum dots,and it is of great significance to promote the development and application of photovoltaic materials with efficient absorption of the solar spectrum.Herein,we designed and synthesized Ag2SexS1-x,Ag2Se and Ag2Te nanocrystals with continuously adjustable bandgap under the guidance of energy band engineering,and expanded their spectral response range.The nucleation growth mechanism,the structure-activity relationship between the energy band gap and the quantum dot size,and the spectrum have been studied in detail.These wide absorption silver-based NIR-? QDs have widespread application potential in the field of photovoltaic materials.The main work is as follows:1.The band gap of Ag2S QDs is 0.92 eV.According to previous research results,the absorption spectrum of Ag2S NIR-II QDs can reach up to about 1100 nm.In order to further expand its absorption spectrum range,we used the Se element doping method to adjust the energy band gap of Ag2S nanocrystals,and successfully prepared Ag2SexS1-x ternary QDs with a narrower band gap to achieve a longer wavelength optical absorption in the NIR-? window.The study found that the QDs gradually change from the monoclinic of Ag2S to the cubic of Ag2Se with the continuous increase of the amount of Se source,which realizes the absorption of larger wavelength spectrum and the continuous adjustment of fluorescence spectrum,covering the entire NIR ?window.In the process of nucleation and growth,Ag2Se actually nucleates and grows first,so the actual reaction is S element doping Ag2Se QDs,and finally the formation of Ag2SexS1-x ternary alloy QDs with high S element content but in the Ag2Se phase state.And the influence of different active Se sources on the nucleation and growth of QDs were explored.2.Ag2Se QDs,as a kind of narrow band gap inorganic semiconductor nanocrystals(0.15 eV),theoretically have excellent optical absorption properties in the long wavelength window of NIR-? region,and also have good optical and chemical stability.Herein,the Ag2Se NIR-? QDs were successfully prepared by using solvothermal injection synthesis method,using silver acetate and trioctylphosphine-Se(TOP-Se)as raw materials,1-dodecanethiol as surface encapsulant,and guided by soft and hard acid-base theory.And the crystal growth process was adjusted to achieve effective adjustment of the energy band gap,and then realized the first exciton absorption peak of Ag2Se NIR-? QDs with continuous adjustable from 950 nm to 1498 nm guided by energy band engineering,and the fluorescence spectrum is continuously adjustable from 1200 nm to 1620 nm.Furthermore,by changing the ratio of cation Ag and anion Se,the dynamic balance of surface capping agent absorption and desorption is realized,thereby changing the reaction rate,and then realizing the continuous growth of QDs and the wider adjustment of energy band gap.3.The band gap of Ag2Te QDs is 0.06 eV.In theory,it also has excellent optical absorption in the long wavelength window of NIR-? region,and it is an ideal photovoltaic absorption material of NIR-? QDs.We used solvothermal injection synthesis method to obtain Ag2Te QDs with continuously adjustable energy band gap,and achieve long-wavelength optical absorption in the NIR-? region.In the experiment,it was found that the optical and chemical properties of Ag2Te QDs were not stable after being purified by a polar solvent.This was attributed to the common dipole-dipole interaction in tellurides that led to the reduction of the binding force between particles.In order to solve this kind of problem,we prepared Ag2Te@Ag2S core-shell structure for the first time by the successive ionic layer adsorption and reaction method(SILAR),and its stability has been enhanced.After the shelling,the shape and wavelength of absorption spectrum and fluorescence peak of the quantum dots did not change.It shows that the core-shell structured QDs are of type ?,and the optical and chemical properties are more stable than before,and the synthesis strategy is suitable for Ag2Te NIR-? QDs with different sizes.More importantly,the fluorescence intensity has been greatly enhanced,indicating that the stable Ag2S shell passivates the dangling bonds on the original surface and reduces surface defects,laying a material foundation for the preparation of high-efficiency photovoltaics.