Fabrication And Simulation Of Colloidal Quantum Dot Infrared Solar Cells

Because of its unique photoelectrical characteristics of solution processability,size-tunable bandgap and efficient multiple-exciton generation,lead chalcogenide（Pb X,X=S,Se）colloidal quantum dots（CQDs）become one of the best candidates for solar cells.Thanks to its narrow bandgap,Pb X CQDs can absorb efficient infrared light,and can be used in the tandem cell with perovskite（Eg=1.58-1.68e V）and c-Si（Eg=1.12e V）materials recently.The highest power conversion efficiency（PCE）of Pb Se CQD solar cells reached to10.68%,which is lower than that of Pb S CQD solar cells（14.0%）.Nowadays,most researchers ignore the optimization of CQDs synthesis,nevertheless,it is the material itself which directly affect the device performance,thus this paper is dedicated to improving the quality of CQDs.Pb X CQDs with uniform size distribution,better surface passivation and superior stability in ambient atmosphere is obtained.The main research results are as followed:1、The quantized Ostwald ripening effect in the growth process of quantum dots is utilized by continuously maintaining the monomer concentration of sulfur or selenium source,and finally the size-distribution of CQDs is improved;the surface reconstruction phenomenon is effectively mitigated by applying low temperature condition during the whole synthesis process,so as to alleviate the exposure of nonpolar（100）facets;the Cl^-ions and Cd²⁺ions contained in the lead and the selenium precursor separately can effectively passivate the CQDs surface.2、After ligand exchange,the organic residuals can be effectively removed,and the halogen ligands are successfully introduced to passivate the surface defect states.The results show that the as-prepared QD films have fewer surface defect states,and the average fluorescence lifetime of Pb Se CQD film is higher than that of previous reports.The devices based on the above-mentioned materials perform well and the large size CQDs solar cells can still retain a certain efficiency after being filtered by silicon wafer.3、The influences of the sample thickness,ions mobility and density of defect states on the performance of solar cell devices were simulated by SCAPS software.The optimal film thickness depends on the width of the depletion zone;the ions mobility has a small impact on the open circuit voltage while that on the external quantum efficiency is greater;the defect states density affects all aspects of the device,but its influence on the short-circuit current and external quantum efficiency is less than that of ions mobility.