Oikonomidis P. Sokratis

“Energy Technologies and Sustainable Design” -Postgraduate Studies, University of Cyprus

“Powder Technology Laboratory”, University of Cyprus

Recycling Si-kerf from Photovoltaics to Thermoelectrics

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Outline• Introduction to thermoelectricity• Phase 1Use of Si-kerf from PV recycling process (Fraunhofer Institute) to form Mg₂Si• Phase 2Doping with Bi-measurements and comparison to previous work• Conclusions

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

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Introduction to thermoelectricityThermoelectricityconversion of temperature difference to electric voltage & charge differential to temperature alternationSeebeck effect: Direct conversion of temperature difference into electricityPeltier effect : Absorbance or Rejection of heat across the junction of two metals, depending on the direction of the applied currentThomson effect : This effect consists of reversible cooling or heating when a flow of electric current and a temperature gradient occur simultaneously.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

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At the junction of two dissimilar metals, electrons migrate in one direction across the junction (thermoelectric current)Increase of ΔT = increase of thermoelectric voltage(due to buildup of charge carriers on the cold side)Seebeck coefficient S

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Introduction to thermoelectricity

Seebeck

S positive when direction of electric current is same as the direction of thermal current

5PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Introduction to thermoelectricity

Peltier

“..An electrical current produce a temperature gradient at the junction of two dissimilar metals..” (Jean Peltier,1834)When an electric current is applied on a thermocouple, the result is an exothermic or an endothermic phenomenon in accordance to the current’s directionPeltier Coefficient

When the current direction was reversed, the cold junction would get hot while the hot would get cold.

6PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Introduction to thermoelectricity

Thomson

Heat energy is absorbed (endothermic) or evolved (exothermic) along the length of a material rod whose ends are at different temperatures. This heat energy was shown to be proportional to the flow of current and to the temperature gradient along the rod.Thomson Coefficient τ

7PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Phase 1Analysis of the recycled material to determine %Si & %SiC

sample consists of 85% Si & 15% SiC

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Forming Mg₂SiFrom Mg + Si-kerf

(SUCCESS)Small percentages of unreacted Si (negligible)

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Phase 1

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 1Measuring thermoelectric performance and comparing to previous work

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 1Measuring thermoelectric performance and comparing to previous workSeebeck Coefficient:

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Measuring thermoelectric performance and comparing to previous workPower Factor: S: Seebeck coefficientσ: electrical conductivityT: Temperature

Phase 1

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Phase 1Measuring thermoelectric performance and comparing to previous workFigure of Merit:

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Bismuth doping2% #A3% #G

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Phase 2

14PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to ThermoelectricsOikonomidis P. Sokratis

Phase 2

Bismuth doping3% #GBrittle behavior

Sample #G with (3% Bi)-exfoliating process

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 2

Electrical conductivity σ (S/cm) in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Seebeck coefficient S (μV/K) in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

Phase 2

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 2

Thermal conductivity κ (W/mK) in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 2

Thermal Lattice conductivity κʟ (W/mK) in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 2

Power Factor in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Phase 2

ZT in#Reference Doped (3% doping)#007 (undoped)#A (2% Bi)#G (3% Bi)in temperature dependence.

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis

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Conclusion• Successful production of Mg2Si from pure Mg & Si-kerf (waste material)• Samples with Si-kerf present similar thermoelectric performance to

previous work from pure Mg and pure Si• 2% & 3% doping presented good PF values relatively to pure Mg2Si

(nominator in ZT equation)• The thermal conductivity decreased as expected due to increased

lattice scattering (denominator in ZT equation)• 2% doping exhibits better ZT and PF values than 3% doping, but both

less than that of pure Mg2Si

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Thank you for your time

PowderTech Lab Project- Recycling Si-kerf from Photovoltaics to Thermoelectrics_Oikonomidis P. Sokratis