20.109 last solar lecture 2014 - Amazon...
Transcript of 20.109 last solar lecture 2014 - Amazon...
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INTRODUCTION
TCO
e-‐
e-‐ I3-‐ I-‐
e-‐
Dye+
Dye
Counter Electrode
Nanopar:cles TiO2 Electrode
q High Surface Area High Dye Loading q Random Electron Pathway Low Diffusion Length
Recombina:on by Electrolyte Redox Couple
Recombina:on by Excited Dye
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INTRODUCTION
Counter Electrode
TCO
e-‐ e-‐ e-‐
Ver:cal Nano-‐tube/rod TiO2 Electrode
q Low Surface Area Low Dye Loading q Direc=onal Electron Pathway High Diffusion Length
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INTRODUCTION
TCO
Counter Electrode
How Carbon Nanotube Helps DSSCs ?
q High Surface Area High Dye Loading q Direc=onal Electron Pathway High Diffusion Length
e-‐
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Faster Transport and Thinner film
Faster transport SWNT as electron pathway
Thinner film Less Absorp=on?? Plasmonics
Nature Nanotechnology, 2011
ACS Nano, 2011
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hKp://www.solaronix.com
Iden=fying the conduc=ve side of the TCO (transparent conduc=ve oxide)
“Doctor-‐blading” the =tania (TiO2) paste
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hKp://www.solaronix.com
Sintering the film (hea=ng)
Dyeing the film
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hKp://www.solaronix.com Assembling the device with another electrode
Filling the electrolyte
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hKp://www.solaronix.com
Tes=ng the device
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Instruments and data to be expected
The Air Mass is the path length which light takes through the atmosphere normalized to the shortest possible path length. The reduc=on in the power of light as it passes through the atmosphere and is absorbed by air and dust.
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the genera=on of light-‐generated carriers the collec=on of the light-‐generated carries to generate a current; the genera=on of a large voltage across the solar cell; and the dissipa=on of power in the load and in parasi=c resistances.
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A voltage results from the electric field formed at the junc=on
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electrolyte
TiO2 dye
counter electrode
S/S+
S+/S*
Electrical work
mediator
Energy level
-‐0.9
-‐0.7
0.2
0.8
ΔV
Mechanism Ac:va:on (1) S|SC (Semiconductor) + hγ → S*|SC
Electron injec:on (2) S*|SC → S+|SC + e-‐cb(SC) Electron collec:on (3) e-‐cb(SC) → e-‐(FTO)
Electron recep:on (7) I3-‐ + e-‐(Pt) → I-‐ Intercep:on (8) S+|SC + I-‐ → S|SC + I3-‐
V vs. SCE
Black Dye (N749)
TiO2 Working Electrode
Pt Counter Electrode
Mask
Electrolyte
INTRODUCTION Mechanism of Dye-‐sensi:zed Solar Cell
1
2
3
0 5
6 7
8
Red Dye (N719)
4
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PARAMETERS I-‐V Curve
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PARAMETERS Short-‐Circuit Current (ISC)
The short-‐circuit current : the genera=on and collec=on of light-‐generated carriers The area of the solar cell. To remove this use short-‐circuit current density (Jsc in mA/cm2) The number of photons. (i.e., the power of the incident light source). The spectrum of the incident light. For most solar cell measurement, the spectrum is the AM1.5 spectrum; The op:cal proper:es. Absorp=on and reflec=on of the solar cell. The collec:on probability of the solar cell, which depends chiefly on the surface passiva=on and the minority carrier life=me in the base.
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The open-‐circuit voltage, VOC, is the maximum voltage available from a solar cell, and this occurs at zero current.
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PARAMETERS Open-‐Circuit Voltage (VOC)
Level of the dye molecule
Energy Level of the redox couple in electrolyte
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PARAMETERS Fill Factor (FF)
Higher FF à Higher efficiency Lower FF à Lower efficiency
The short-‐circuit current and the open-‐circuit voltage are the maximum current and voltage respec=vely from a solar cell. However, at both of these opera=ng points, the power from the solar cell is zero. The "fill factor", more commonly known by its abbrevia=on "FF", is a parameter which, in conjunc=on with Voc and Isc, determines the maximum power from a solar cell
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PV cells can be modeled as a current source in parallel with a diode. When there is no light present to generate any current, the PV cell behaves like a diode. As the intensity of incident light increases, current is generated by the PV cell
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The efficiency of a solar cell is determined as the frac=on of incident power which is converted to electricity and is defined as :where Voc is the open-‐circuit voltage; where Isc is the short-‐circuit current; and where FF is the fill factor where η is the efficiency.In a 10 x 10 cm2 cell the input power is 100 mW/cm2 x 100 cm2
= 10 W.
The efficiency is the most commonly used parameter to compare the performance of one solar cell to another. Efficiency is defined as the ra=o of energy output from the solar cell to input energy from the sun.
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PARAMETERS Quantum Efficiency
q The ra:o of the number of carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell.
q While the QE ideally has the square shap, the QE for most solar cells is reduced due to recombina=on effects. The same mechanisms which affect the collec=on probability also affect the QE.