Fabrication And Optimization Of Lead Sulfide Colloidal Quantum Dots Solar Cells

Colloidal quantum dots(abbreviated as CQDs,also known as Colloidal Nanocrystals)are nanoscale crystals of bulk semiconductor crystals.Through tailoring the size,shape or composition,the optical and electrical properties of CQDs can be easily adjusted which made them promosing candidates for advanced semiconductors.The large specific area of CQDs surface play an important role in determination of its properties.The doping type,charge earrier concentration of CQD semiconductor can be tuned through changing its surface ligand.This advantages in processibihty combining with compatibility of solution processing make CQDs powerful materials for device engineers.In this thesis,the excellent processibihty of CQDs and its impact on deposition techniques,film morphology and electrical properties of quantum dots films will be discussed first.The application of CQDs on single junction and tandem solar cellswill be further introduced.The research topics were divided into 4 chapters as follows:Chapter l:The basic optical and electric properties of CQDs and its related photovoltaic technique.The surface engineering leading to specificly tunable properties of CQDs will be introduced in this chapter followed by the progress of CQDs application on single junction solar cells and tandem solar cells.Chapter 2:Single junction solar cells based on planer structure and ordered ZnO nanoarrays(ZnO NRs)substrate deposited through convective assembly.The ligand exchange process,morphology of PbS CQDs films and CQDs/ZnO NWs interfaces as well as device aging process were carefully studied.The capillary driving force provide CQDs-CQDs and CQDs-substrate the attractive potential which pull CQDs into their maximum packing density within the thin film.The improved morphology of CQDs film benefits carrier mobility,reduction of the defeacts and thus better device performance.This improvement was demonstrate on CQDs device based both on planer structure and ordered ZnO NRs substrate which provide instructive insight on fabrication of high一efficient CQDs photovoltaic devices.Chapter 3:Stable,high-performance PbS colloidal quantum dots tandem solar cells with simplified structure were fabricated under ambient air.In this chapter,detailed device engineering to deposit each functional layer in the subcells at low temperature process were revealed which makes the fabrication process compatible to flexible plastic substrate.The use of robust inorganic RL containing an ultrathin Au interlayer results in more efficient device performance and remarkably improved device lifetime.The remarkable stability,high performance,and low-temperature processing of these tandem devices may provide insight into the commercialization of flexible and large-area CQDs tandem solar cells in the near future.Chapter 4:The combinative effects of thermal annealing and additive processes on the performance of all-polymer bulk heterojunction(BHJ)solar cells provide a simple and versatile method to improve all-polymer single junction solar cells.Moreover,an efficient all-polymer tandem cell utilizing identical sub-cells were achieved through which the deficiency of short carrier diffusion length of organic polymers can be overcame.The efficient absorption of light energy and the carrier collection in this homo-tandem solar cells remains efficient by insetting a recombination layers between two active layers with identical all-polymer components.Based on previous results,solution processed hybrid tandem solar cells made of colloid quantum dots and organic semiconductors were demonstrated.This hybrid tandem solar cell made from a combination of CQDs and polymer/polymer blends enabling efficient capture of solar emission among visible and near infrared region fabricated through solution process.The detailed devices fabrication and optimization were revealed which introduce a referential results to achieve highly efficient hybrid tandem solar cells.