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# [http://live.gnome.org/Dia Dia] is a program that creates elaborate flowcharts and diagrams to simplify complicated processes.  The figure displayed to the right outlines the basic steps to prepare and 3-D print CdSe and PbS quantum dots.  The detailed formation of these two semiconductors is shown below
# [http://live.gnome.org/Dia Dia] is a program that creates elaborate flowcharts and diagrams to simplify complicated processes.  The figure displayed to the right outlines the basic steps to prepare and 3-D print CdSe and PbS quantum dots.  The detailed formation of these two semiconductors is shown below
[[Image:QDSC Synthesis.png|thumb|Fig. #: General Process for 3-D printing CdSe and PbS quantum dots as thin film solar cells]]
[[Image:QDSC Synthesis.png|thumb|Fig. #: General Process for 3-D printing CdSe and PbS quantum dots as thin film solar cells]]
{{gallery|width=600|height=1300|lines=4|Image:CdSe QD Synthesis.png<ref>http://education.mrsec.wisc.edu/300.htm Cadmium selenide quantum dot synthesis</ref>|Fig. # CdSe quantum dot synthesis:|Image:PbS QD Synthesis.png<ref>http://pubs.rsc.org/en/content/articlelanding/2012/CE/c3ce26976k#!divAbstract Rapid synthesis of PbS colloidal quantum dots</ref>|Fig. #: PbS quantum dot synthesis}}
{{gallery|width=600|height=1300|lines=4|Image:CdSe QD Synthesis.png|Fig. # Cadmium selenide quantum dot synthesis <ref>http://education.mrsec.wisc.edu/300.htm October 16, 2013</ref>|Image:PbS QD Synthesis.png |Fig. #: Rapid synthesis of PbS colloidal quantum dots <ref>http://pubs.rsc.org/en/content/articlelanding/2012/CE/c3ce26976k#!divAbstract October 16, 2013</ref>}}


==8==
==8==
# Outline purification methods and the methods needed to obtain acceptable purity for your material.
# Outline purification methods and the methods needed to obtain acceptable purity for your material.PbS quantum dot synthesis


==9==
==9==

Revision as of 11:12, 16 October 2013

Quantum dots (QD) are nanoparticles comprised of semiconductor materials, which exhibit enhanced electronic properties over bulk materials. These properties are defined by a highly adjustable structure of the quantum dot that yields enormous potential in many applications, including photovoltaic cells. [1] A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell (in that its electrical characteristics—e.g. current, voltage, or resistance—vary when light is incident upon it) which, when exposed to light, can generate and support an electric current without being attached to any external voltage source. [2] If combined with a quantum dot, a high quantum efficiency (percentage of photons transformed into current) is produced, generating a usable total efficiency.[3]The viability of dissolving these quantum dots into a suitable ink for 3-D printing onto a universal solar cell and its processes are analyzed and discussed.

Solar cell concept[4]

Overview

Quantum dot solar cells are often made by depositing quantum dots on thin film ceramics[5].


3-D Printed Device

The layers of the semiconductor portion are raised above a solar cell template: CdSe(crimson), mixed layer(dark red), PbS(Grey)

The scope of this project focuses on photovoltaic cells utilizing CdSe and PbS quantum dots to convert photon energy into current. This particular solar cell will consist of three layers: a p-type (PbS) layer on top; a bulk nano-heterojunction (BNH), or mix of two quantum dots, in the middle; and an n-type (CdSe) layer on the bottom. Each ink will only be deposited in one layer by the 3-D printer (the layer thickness of 0.3 mm in RepRaps[6] is already much thinner than the typical nano-scale, except for the CdSe layer, which will be deposited twice. This is because the increased n-type doping is suggested in BNH devices, as well as a 1:2 p-type to n-type ratio[7]). Complete solidification between ink applications may not be necessary, as intermixing between layers may expand the BNH. There will also be carbon nanotubes dispersed throughout the layers to enhance conductivity.

The matrix that the quantum dots and single wall carbon nanotubes (SWNT's) would work in is ABS. ABS is already used in many 3-D printing applications. It was selected because it has a low enough printing temperature (about 220° C) to work in a low temperature extruder, but a high enough temperature to retain its properties despite extended periods of time in direct sunlight. To prevent cracking when it is deposited, the plate will be warmed. The ABS that would be used has a resistance of 104 ohm-cm, which will be improved by the addition of SWNT's.

Materials and Processing

  1. A detailed BOM of the chemicals used to make it with links to sources and prices in a table - and total cost.

5

  1. Links to MSDSs for each of the chemicals.

6

Ink Synthesis

Sites have been found that would allow us to buy the QD's, ABS, and SWNT's. It can be seen from NOM corp's website is that the CdSe QD's absorb light between 500-600nm, which takes care of most of the visible light spectrum. The Dia graphic describes how QD's could be synthesized at home.

The semiconductor will be made using 3 separate inks: a PbS ink, a CdSe ink, and a mixed ink. All of these inks should have 1x1016[8] QD's per cm3 and 100 mg/L of SWNT's[9]. Based on these concentrations and a print volume that was determined to be 1.95 cm3, the necessary quantities of each material is given in the 'Amount Needed' column of the bill of materials. This process will require a hopper, a heater, a screw extruder, and a mold. The synthesis process of each ink can be summarized with these steps:

  1. The ABS will be melted at 250° C.
  2. The melted ABS and appropriate concentrations of QD's and SWNT's will be mixed in a hopper.
  3. The liquid ink will be extruded in a mold with the same dimension (1.75 mm diameter) as before.

7

  1. Dia is a program that creates elaborate flowcharts and diagrams to simplify complicated processes. The figure displayed to the right outlines the basic steps to prepare and 3-D print CdSe and PbS quantum dots. The detailed formation of these two semiconductors is shown below
Fig. #: General Process for 3-D printing CdSe and PbS quantum dots as thin film solar cells

8

  1. Outline purification methods and the methods needed to obtain acceptable purity for your material.PbS quantum dot synthesis

9

  1. A description of the testing procedures, equipment and specifications for the equipment used to determine if you obtained your target compound.
Semiconductor band gap and structure .

5

High-Resolution Transmission Electron Microscopy (HRTEM) HRTEM is a powerful tool for analysis of properties of materials on the atomic scale. 1 At present, the highest point resolution realized in phase contrast TEM is around 0.5 ångströms (0.050 nm). Phase contrast TEM enables high resolution imaging. 1.This is ideal for semiconductors and in this case, a quantum dot solar cell because individual atoms of a crystal and its defects can be found. Another very important aspect of this analysis is that size of particles can be measured, as well as their distribution. Other uses of this method are

  • Light microscopy using the different refractive indices for differing structures 2
  • X-ray imaging with diffraction contrast through Bragg scattering
  • Elemental composition analysis based on unique electron energies

Description of procedure: 3

1. Gloves will be worn whenever handling sample or holders.

2. Sample will be prepped for operation.

3. After sample is loaded, the microscope will be brought to operating conditions slowly.

4. The condenser lens, objective lenses, voltage and current centers will be aligned.

5. The accelerating voltage will be reached and an electron beam will be generated.

6. Testing until satisfaction and then sample will be removed.


Optical Absorption

When a light is shining on a semiconductor sample, if the energy of the individual photons is greater than the semiconductor band gap, then the photons can be absorbed, transferring their energy to an electron. This is the basis behind optical absorption. 4 The light shined on the sample will be transmitted and then measured by a photodetector. By observing the wavelength at which the sample begins to absorb the light, the bandgap of the sample can be determined. Light incident, reflected, transmitted or scattered by the sample or holder will be absorbed, thus accuracy is important. Intensity of light absorbed can be measured, the fraction of light reflected can be measured, and transmissivity can be measured to yield information about the sample. 4 This information can be complied to gain an idea of how effective a solar cell is.

1. http://en.wikipedia.org/wiki/High-resolution_transmission_electron_microscopy 2. http://en.wikipedia.org/wiki/Phase-contrast_imaging 3. http://ncmn.unl.edu/cfem/about/operating_procedure_HRTEM.shtml#sample 4. http://classes.soe.ucsc.edu/ee145/Spring02/EE145Lab8.pdf 5. http://en.wikipedia.org/wiki/Band_gap

Testing

Quantum dot semiconductor containing concept CdSe a n-type semiconductor(Red) and PbS a p-type semiconductor (Grey) with a bulk nano-heterojunction separating the layers.

Ideal Semiconductor Ink Properties

This ink is mostly focused on extending the lifetime of charge carriers in the semiconductor. However, another factor that should be considered in the making of this ink, as in all photovoltaic cells, is the range and efficiency of the absorption of photons. These properties will help increase the efficiency of the ink.

  1. Homogenous distribution of carbon nanotubes among the quantum dots will help conduct improve its ability to act as a charge acceptor.
  2. Homogenous distribution of the quantum dots allows for more efficient use of the surface area.
  3. Intermixing of the p-type and n-type QD's in the middle layer to allow a greater interfacial area for diffusion to occur to the junction before recombination occurs within the p- or n-section[10].
  4. Range of QD diameters so that a wide range of photon energies can be absorbed[11].
  5. Thin layers.

In-Situ Analysis

This process takes the trouble of melting and re-solidifying the ABS in a form compatible with the low temperature extruder before 3-D printing the ink. This allows us to perform in-situ analysis on the ink before it is printed.

To test the homogeneity of the quantum dots within the ABS, it would be useful to section off some of the semiconductor ink and take an SEM (scanning electron microscope) image of the section. A coating of chromium or graphite may need to be applied if the ink is not conductive enough[12]. This in-situ analysis would allow the mixing of the QD's to be tested before they are printed out as a solar cell. Also, if a range of QD sizes are observable within the solidified ink, it follows that a range of photon energies will be able to be observed.

If the ink is not suitably homogenous, the ABS ink can be remelted and remixed, possibly at a higher temperature to increase solubility. This in-situ analysis can be repeated until the ink is suitably homogenous.

Post-fabrication Testing

  1. A description of the testing procedures, equipment and specifications for the equipment used to determine if you obtained your target compound.

Discussion

3-D Printing Applications

Compiled and rendered version of the quantum dot layers on the face of a watch

Everyone has already seen the old calculators that use solar cells to help power them. It's quite probable that in the future many smart phones, tablets, and other user devices will run on solar power as well. Our application uses a material that many believe will greatly improve solar cell efficiency, quantum dots, as the solar cell semiconductor for these consumer devices. 3-D printing is the superior way to deposit quantum dots onto these devices. Several other techniques are used to deposit quantum dot semiconductors onto surfaces. These include templated assembly and spin casting. However, 3-D printing has an advantage for printing solar cells over both of these deposition techniques.

  • The templated assembly requires that a pattern produced by a resist be placed on the substrate where the QD's are supposed to go. This allows for very precise placement of QD's, but is usually only used if one type of QD is to be deposited[13]. For solar cells using a p-type and an n-type layer, putting a resist on top of the bottom layer may disrupt the properties of the interface between the layers.
  • Spin casting, on the other hand, allows for multiple layers, such as QD's and graphene, to be deposited on substrate, but it lacks precision [14]. Spin casting uses a flat wheel spinning rapidly to distribute the solution uniformly across the surface of the substrate. It does not allow for depositing around designs or across surfaces that are not extremely flat.

The watch design displayed in the OpenScad shows the advantages of 3-D printing a small photovoltaic cell using QD's. It allows for different design choices to be made, such as the holes for separate dials in the watch, while still depositing layers evenly across the surface. It also allows for multiple layers, which a photovoltaic cell requires, to be deposited. Some limits are still in place before user devices will be a reasonable place to use this application. PbS is a heavy metal, which is disapproved of in society for consumer products due to its toxicity level. Also, these cells could improve in efficiency by reducing thickness. However, quantum dot materials and 3-D printing layer thickness are sure to improve in the future, making this a very powerful application. http://www.appropedia.org/File:Watch_Face_STL.stl


The layers of the semiconductor portion CdSe(crimson), mixed layer(dark red), PbS(Grey) are shown as they would be printed
Colored rendition of the quantum dot semiconductor on the face of a wrist watch
The PbS(grey) is raised with a conceptual view of the ideal mixed layer being a homogeneous mixture
The layers of the semiconductor portion are shown to display thickness CdSe(crimson), mixed layer(dark red), PbS(Grey)


Code for wrist watch:

translate ([0,0,-3.005]) {color ("Black",1) cylinder (h = 3.5, r=25, $fn=100);}

// cutting into the first 2 layers (CdSe)

difference() {

translate ([0,0,.5]) {color ("Crimson",1) cylinder (h = 1.5, r=25, $fn=100);} translate ([0,7,1]) {color ("Crimson",1) circle (6.5, $fn=50); }

translate ([7.25,-5.5,1]) {color ("Crimson",1) circle (6.5, $fn=50); }

translate ([-7.25,-5.5,1]) {color ("Crimson",1) circle (6.5, $fn=50) ; }

}

// cutting into the mixed layer (CdSe + PbS)

difference() {

translate ([0,0,2]) {color ("DarkRed",1) cylinder (h = 1, r=25, $fn=100);} translate ([0,7,1.995]) {color ("DarkRed",1) cylinder (h = 1.5, r=6.7, $fn=50);}

translate ([7.25,-5.5,1.995]) {color ("DarkRed",1) cylinder (h = 1.5, r=6.7, $fn=50);}

translate ([-7.25,-5.5,1.995]) {color ("DarkRed",1) cylinder (h = 1.5, r=6.7, $fn=50);}

}

// cutting into the final layer (PbS)

difference() {

translate ([0,0,3]) {color ("Grey",1) cylinder (h = 1, r=25, $fn=100);} translate ([0,7,2.995]) {color ("Grey",1) cylinder (h = 1.5, r=6.9, $fn=50);}

translate ([7.25,-5.5,2.995]) {color ("Grey",1) cylinder (h = 1.5, r=6.9, $fn=50);}

translate ([-7.25,-5.5,2.995]) {color ("Grey",1) cylinder (h = 1.5, r=6.9, $fn=50);}

}

translate ([1,17,1]) {color ("Gold",1) cube([1,6,4]); }

translate ([-1,17,1]) {color ("Gold",1) cube([1,6,4]); }

translate ([-23,0,1]) {color ("Gold",1) cube([6,1,4]); }

translate ([0,-23,1]) {color ("Gold",1) cube([1,6,4]); }

translate ([17,0,1]) {color ("Gold",1) cube([6,1,4]); }

rotate([0,0,60]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,30]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,120]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,150]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,210]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,240]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,300]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

rotate([0,0,330]) translate ([17,0,1]) {color ("Black",1) cube([6,1,4]); }

translate ([0,-1.5,0]) {color ("White",1) cylinder (h = 6, r=1, $fn=50);}

rotate([0,0,35]) translate ([-1,-2,6]) {color ("White",1) cube([14,1.5,1]); }

rotate([0,0,270]) translate ([1,-.5,6]) {color ("White",1) cube([18,1.5,1]); }

rotate([0,0,120]) translate ([-1,.5,6]) {color ("White",1) cube([22,.5,1]); }

// small circles

rotate([0,0,0]) translate ([0,4,1]) {color ("White",1) cube([.5,6,.5]); }

rotate([0,0,0]) translate ([-2.75,6.75,1]) {color ("White",1) cube([6,.5,.5]); }

rotate([0,0,235]) translate ([-.25,6,1]) {color ("White",1) cube([.5,6,.5]); }

rotate([0,0,235]) translate ([-2.75,8.75,1]) {color ("White",1) cube([6,.5,.5]); }

rotate([0,0,135]) translate ([.5,6,1]) {color ("White",1) cube([.5,6,.5]); }

rotate([0,0,135]) translate ([-2.25,8.75,1]) {color ("White",1) cube([6,.5,.5]); }


Deliverables

  1. Create your team project page and add the template {{MY3701}}-Complete
  2. A brief description of your semiconductor material with a link to the manufacturer(s) or suppliers of it if it exists on the market.
  3. A description of how it could be 3-D printed (e.g. compare properties like viscosity or melting temperature to existing known printable material)
  4. A detailed BOM of the chemicals used to make it with links to sources and prices in a table - and total cost.
  5. Links to MSDSs for each of the chemicals.
  6. A detailed description of the steps, equipment and amounts of chemicals needed to synthesize the semiconductor ink with references to sources (e.g. recipe)
  7. Create a diagram in Dia outlining your workflow to summarize the steps, and the equipment, processes, chemicals, steps involved. Show alternate paths and discuss the optimal route and the metrics for choosing it. Post image on project page and email Dr. Pearce your Dia file.
  8. Outline purification methods and the methods needed to obtain acceptable purity for your material.
  9. A description of the testing procedures, equipment and specifications for the equipment used to determine if you obtained your target compound.
  10. A list of best in class material properties for your ink.
  11. Discuss the characterization methods and how they could be adapted for in-situ analysis.
  12. List and describe applications of this semiconductor if it is printed.
  13. Make a basic diagram for an electronic device that could use this semiconductor and post diagram in your project page.
  14. Design the semiconductor portion of the device in OpenSCAD, paste the code directly into your project page
  15. Post the STL of your design and a link to the STL on your project page.




See Help:Tables and Help:Table examples for more.

References

  1. Wikipedia: Quantum Dot October 16, 2013
  2. [Solar Cell - Wikipedia] October 11, 2013.
  3. Wikipedia: Quantum Dot Solar Cell October 16, 2013.
  4. Solarcellcentral October 11, 2013.
  5. QD solar cell company October 15, 2013
  6. RepRap layer thickness October 10, 2013
  7. BNH ratio October 10, 2013
  8. QD concentration October 10, 2013
  9. SWNT concentration October 14, 2013
  10. BNH interface October 14, 2013
  11. Diameter and absorption October 6, 2013
  12. SEM info October 14, 2013
  13. Templated assembly of CdSe October 6, 2013
  14. Spin casting with QD's and graphene October 6, 2013

Contact details

Add your contact information.

Template:MY3701

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