Study On Synthesis And Surface Passivation Of PbS Quantum Dots

The advantages of lead sulfide quantum dots(PbS QDs),such as wide tunable bandgaps,large Bohr radius(18 nm),controllable size,simple preparation method and potential multi-exciton effect,have great application value in the fields of solar cells and photodetectors.However,the oleic acid(OA)wrapping on the surface of PbS QDs synthesized by thermal injection method hinders the carrier transmission.At the same time,PbS QDs also have the problem of high surface dangling bonds,which will have a harmful effect on their photoelectric performance.This paper studies the synthesis and passivation process of PbS QDs,and explores the effects of passivation methods on the characteristics of PbS QDs thin films and the photoelectric properties of PbS/Al Schottky junctions.The main work and results are as follows:1.The PbS QDs were synthesized by the thermal injection method,and the controllable modulation of the photoluminescence(PL)spectrum of the PbS QDs was achieved by adjusting the cooling rate.The results show that as the cooling rate increases,the band gap of the QDs becomes wider,the PL and the absorption spectrum appear blue-shifted.The PL peak becomes sharper and the full width at half maximum(FWHM)becomes narrower.When the cooling rate is 10?/min,the reaction temperature is 90?,and the reaction time is 5 minutes,the prepared PbS QDs have a size of 3.42 nm,a band gap of 1.21 eV,and absorption and PL spectra are located in the near infrared region.2.Compared the effect of three passivation processes,including solid-state exchange method,solution method and hybrid passivation method on the characteristics of PbS QDs films.The results show that the best passivation effect is the hybrid passivation method.The OA-wrapping on the surface of PbS QDs was almost completely removed,and a large amount of iodide ions(I-)was introduced to wrap on the surface of QDs,reducing dangling bonds on the surface of the PbS QDs and improving the carrier transport capacity.3.The optical and electrical properties of PbS/Al Schottky junction were prepared and studied.The results show that the photoelectric characteristics of the QDs Schottky junction passivated by the hybrid passivation method are the best.Compared with the performance of the unpassivated QDs Schottky junction,under the-2V bias,the PbS/Al Schottky junction photocurrent density increased from 3.6 ×10-11 A/cm2 to 1.2 ×10-7 A/cm2,and the switching ratio increased from 2.5 to 565.5.