Quantum dot solar cell thesis

The origin of sub-bandgap states was further found to be most likely from undercharged Pb atoms on the QD surface off-stoichiometry. In the use of iodide as a ligand that does not bond to oxygen was introduced.

We found that the overall power conversion efficiency of these QDSSCs is largely limited by the surface area of the nanowires available for QD adsorption. The device shows improved performance as a result of the Quantum dot solar cell thesis band alignment between these QD layers, as confirmed by ultraviolet photoelectron spectroscopy.

We found that the photovoltage obtained in these devices depends on QD size and increases linearly with the QD effective bandgap energy. This energy difference is consistent with the below-bandgap activation energy for diode current generation obtained from current-voltage characteristics at different temperatures.

Spin-casting may allow the construction of "tandem" cells at greatly reduced cost. Single junction implementations using lead sulfide PbS colloidal quantum dots CQD have bandgaps that can be tuned into the far infrared, frequencies that are typically difficult to achieve with traditional solar cells.

The ability to tune the bandgap allowed the designer to select a wider variety of materials for other portions of the cell. When using a liquid electrolyte as the hole transport medium, our quantum-dot-sensitized nanowire solar cells exhibited short-circuit current densities up to 2.

Background[ edit ] Solar cell concepts[ edit ] In a conventional solar cell, light is absorbed by a semiconductorproducing an electron-hole e-h pair; the pair may be bound and is referred to as an exciton.

The internal electric field is created by doping one part of semiconductor interface with atoms that act as electron donors n-type doping and another with electron acceptors p-type doping that results in a p-n junction.

A device with this architecture reached a certified efficiency of 8. However, the lattice mismatch results in accumulation of strain and thus generation of defects, restricting the number of stacked layers.

At low production scales quantum dots are more expensive than mass-produced nanocrystals, but cadmium and telluride are rare and highly toxic metals subject to price swings. Owing to the versatile surface chemistry and high surface-to-volume ratio of QDs, the surface ligands play crucial roles in determining the optoelectronic properties.

Toward efficient and stable quantum dot solar cells : design and characterization

Thesis or Dissertation Abstract Environmentally clean renewable energy resources such as solar energy have gained significant attention due to a continual increase in worldwide energy demand.

It is concluded that the VOC of present QD solar cells is mainly limited by the sub-bandgap states rather than the interfaces between QDs and other materials. Thus, we were able to construct solar cells with thick QD absorber layers that were still capable of efficiently extracting charge despite short exciton or charge carrier diffusion lengths.

Thin-films of amorphous siliconwhich due to a relaxed requirement in crystal momentum preservation can achieve direct bandgaps and intermixing of carbon, can tune the bandgap, but other issues have prevented these from matching the performance of traditional cells.

DSSCs use a sponge-like layer of TiO 2 as the semiconductor valve as well as a mechanical support structure. The morphology of the nanowires then provided these photoinjected electrons with a direct and efficient electrical pathway to the photoanode. The device stability has been significantly improved in this work by identifying two key factors that limit the device stability.

This pair is separated by an internal electric field present in p-n junctions or Schottky diodes and the resulting flow of electrons and holes creates electric current. The same analysis shows that a two layer cell should have one layer tuned to 1.

Modern thin-film cells remain generally less efficient than traditional silicon. Unfortunately, the QDs used to make these devices corrode in the presence of the liquid electrolyte and QDSSC performance degrades after several hours.

When illuminated with the AM1.

Quantum dot solar cell

Droplet epitaxy growth technique shows its advantages on the fabrication of strain-free QDs. Department of Materials Science and Engineering. Massachusetts Institute of Technology Date Issued: It is possible to improve on a single-junction cell by vertically stacking cells with different bandgaps — termed a "tandem" or "multi-junction" approach.

The dots can be distributed on a substrate by spin coatingeither by hand or in an automated process. Such cells create the possibility of uncoated "spray-on" cells.

The origins of the large open-circuit voltage VOC deficit, a primary limiting factor in present QD solar cells, have also been investigated through a combination of device physics and spectroscopic studies. A three-layer cell should be tuned to 1.Selecting Semiconductor Materials For The Quantum Dot Intermediate Band Solar Cell A Thesis Submitted to the Faculty of Drexel University by Steven Evans Jenks.

Silver Nanowire Transparent Conductors for Quantum Dot Photovoltaics Natasha Hjerrild St. Edmund Hall A thesis submitted for the degree of MSc in Materials.

quantum dot solar cell e ciency is %[3]. Quantum dot based solar cells are still limited by the trade-o between absorption of light and transport of electrons for providing electricity.

Adding more quantum dots would increase photon absorption but results in worse electron transport and therefore a decrease in e ciency. Abstract In this thesis, I have been working with the development of nanoparticle sensitized solar cells.

In the subarea of quantum dot sensitized solar cells. For example, nanometer-size semiconductor crystallites, or semiconductor quantum dots (QDs), can be used as photoactive materials in solar cells to potentially achieve a maximum theoretical power conversion efficiency which exceeds that of current mainstay solar technology at a much lower cost.

A quantum dot solar cell (QDSC) is a solar cell design that uses quantum dots as the absorbing photovoltaic material. It attempts to replace bulk materials such as silicon, copper indium gallium selenide (CIGS) or CdTe.

Quantum dot solar cell thesis
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