Integrated Solar Cells Based On Lead Sulfide Quantum Dots:Morphology Control,Device Engineering And Photovoltaic Properties

In the past decade,solution-processed lead sulfide(PbS)colloidal quantum dots(CQDs)have received great attention due to their high bandgap tunability,strong near-infrared(NIR)absorption,multiple exciton generation,and ambient processability.In addition,the electrical proptiese of these QDs like charge carrier mobility,doping concentration can be fine-tuned through QDs surface ligand engineering.These excellent and unique properties make it attractive for future developments of QDs based optoelectronic devices such as solar cells,including single-junction and multiple-junction solar cells.Although the efficiency of PbS QD solar cells has been greatly improved,it still lagged significantly behind the theoretical efficiency.Therefore,more efforts are needed to be dedicated into both QDs material and solar cell device optimization.In this project,we thoroughly investigated integrated PbS QDs solar cells with the combination of other solution-processed semiconducte materias,such as organic/PbS QDs solar cells and perovskite/PbS QDs tandem solar cells.The project is divided into 3 sections as follows:Chapter ?:In order to develop high-performance organic/PbS QDs integrated solar cells,we first need to choose suitable organic materials with desired properties.The optical properties and energy levels of organic semiconductors can be easily tuned through the modification of their molecular structures.In order to achieve efficient organic/PbS QDs integrated devices,the morphology of organic bulk heterojunction film was studied.We chose organic carboxylic acids as an effective solvent additive to optimize the polymer-polymer blend morphology and improved the efficiency and stability of all-polymer solar cells.Then,we further studied the effect of D/A ratio on the performance and stability of non-fullerene solar cells.This work provides insights for both materials design and device fabrication of organic/PbS QDs integrated solar cells.Chapter ?:Desgin and preparation of PbS QD/organic heterojunction integrated solar cells.We have successfully demonstrated the effect of thin organic bulk-heterojunction(BHJ)interlayer on improving the open-circuit voltage(V_oc)PbS CQD solar cells.A series of organic BHJ films with PTB7-Th blended with various N-type acceptors have been used as hole transporting layer(HTL)in PbS QDs solar cells.Solution-processed hybrid CQD/organic architecture may become a general approach to improve the performance and scalability of PbS QDs solar cells.Chapter ?:It still remains a huge challenge to integrate fragile perovskite film in a monolithic tandem structure.We for the first time addressed the challenge of preparation of stable and efficient tandem solar cells combining PbS QDs with emerging MAPbI₃ perovskite by solution-processing.Our work provided an important starting point for the future advance in efficient QDs/perovskite tandem solar cells with with more complementary absorption.