Assembly And Interface Manipulation Of PbS Quantum Dots Solar Cells

Lead sulfide quantum dots(PbS QDs)with strong quantum confinement effect,multiple exciton effect and solution processability have shown enormous potential in new-generation,low-cost solar cells.Over the past two decades,the power conversion efficiency(PCE)of PbS QD solar cells has increased from<1%to 14%through surface chemistry and device engineering study.Nevertheless,PbS QD solar cells currently suffer from complex preparation processes and poor device performance,which limit their practical applications.In this paper,we systematically studied the QD assembly behavior during the ligand exchange process.It was shown that the cracks generated during the ligand exchange can be effectively suppressed through manipulating the morphology of PbS QDs and the solvent selection,which can largely simplify the manufacture of devices.Furthermore,we introduced perovskite QDs as an interfacial layer to promote hole extraction and reduce interfacial charge recombination in PbS QD solar cells,which can efficiently improve photovoltaic performance.The specific research results are listed as follows.Chapter 1:The introduction of PbS QD solar cells.The properties of QDs,synthesis methods and the progress of QD solar cells are briefly described.Chapter 2:Simplifying the fabrication of the QD solar cells through assembly manipulation.During the synthesis of QDs,long-chain alkyl ligands are applied to control the nucleation and growth process.However,these long alkyl ligands have to be exchanged with short ones or atomic ligands to render QDs film semi-conducting for optoelectronic application.This process is inevitable to induce detrimental cracks because of the ligand volume loss.Multiple deposition steps are required to fill the cracks,which makes the fabrication process complicated.In this work,we showed an advanced solidstate ligand exchange strategy to achieve crack-free PbS nanocrystal film via a single deposition step,through modulating nanocrystals morphology in combination with solvent engineering,which can effectively control the assembly behavior of nanocrystals.This strategy reveals splendid versatility for films with different thicknesses,substrates and areas.The remarkable property of the nanocrystals film is verified by solar cells as a typical application.The photovoltaic performance is on-par with the recorded current PbS QDs solar cells.Our method possesses benefits of simplicity,"greener" processing and reduction of the material costs,revealing possibility as a facile and dependable approach to preparing high-quality QDs films for optoelectronic applications.Chapter 3:Perovskite bridging PbS QDs/polymer interface enables efficient solar cells.Perovskite is a new type of "soft material"with physical properties between traditional inorganic and organic materials,which is expected to modify the organic/inorganic interface.Moreover,cesium lead triiodide quantum dots(CsPbI3 QDs)and PbS QDs are the most two popular solution-processed QD materials for thin-film solar cells.The appropriate energy level of CsPbI3 QDs falls between the active PbS QDs and the organic PTB7-Th layer.The formed graded band alignment can promote hole extraction and reduce interfacial charge recombination.Meanwhile,the interfacial layer also produces a dipole-charge distribution at the CsPbI3 QD/PbS QDs interface,which improves charge collection and enhances Voc.As a result,the PCE can be efficiently improved from 10.50%to 12.32%.This work highlights the importance of interfacial manipulation in QDs solar cells and proposes a new direction to design advanced device architectures by the combinative use of two typical solution-processed QDs photovoltaic materials.