External Quantum Efficiency
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- 1. External Quantum Efficiency (EQE)Measurement Prasad Gandhi Advisor: Dr. Brendan OConnor 9/23/2011
2. Solar cell technologies Silicon GaAs CuInGaSe CdTe -Si + organic semiconductors 9/23/2011 3. Can organic solar cells make an impact?
- Organic solar cell potential:
- Low materials cost
- Mechanical flexibility
- Compatible with low-cost processing
- Simpler installation
* Source: DOE Utility Scale System cost ($/W) (Business as usual) DOE Goal: $1/W ~ 0.05-0.06 $/kWh (competitive with wholesale rates of electricity) Efficiency ~ 10% Requires module: $50/m 2 9/23/2011 4. National Renewable Energy Laboratory, 2011 Best Si Best Organic 25.0% 8.3% Solar cell efficiency trends 9/23/2011 5. The generation of electricity from light using organic molecules(made primarily from Carbon) Organic solar cells? 9/23/2011 6. Organic solar cells? 9/23/2011 7.
- Organic solar cell processes :
- Photon absorbed, ( A ~100%)
- Excited states diffuse,( ED ~10%)
- Charged formed at Donor Acceptor interface,( CT~100%)
- Charge diffuses out,( cc ~100%)
x glass electrode electrode ~100 nm External Quantum Efficiency 9/23/2011 8. Bulk heterojunction organic solar cell + - Transparent substrate Transparent Electrode (ITO)/ PEDOT:PSS Active Layer (BHJ) P3HT:PCBM Electrode (LiF/Al) h 9/23/2011 9. Key parameters and equations p j scV oc FF Current - voltage curve Quantum efficiency Solar cell characteristics 9/23/2011 10.
- Provides information on current a solar cell will produce when illuminated by a particular wavelength of light.
- EQE integrated over the solar spectrum predicts the photocurrent that a solar cell will produce when exposed to the solar spectrum.
Why measure EQE? Quantum efficiency 9/23/2011 11. EQE Testing Equipment Setup
- Solar Simulator & Power Supply
- Organic Solar Cell (OSC)
- Optical Chopper and controller-
- Lock-In Amplifier
9/23/2011 12. External Quantum Efficiency Setup Monochromator Lamp Photo Diode Controller Optical Chopper 9/23/2011 Fig a) Front side Fig b) Backside 13. Getting the number of photons Initial calibration of light at given wavelength measured with a calibrated photo-diode, this gives us the number of photons 9/23/2011 14. Performance relative to reference commercial solar cell Fig. Responsivity Curve of Hamamatsu photo diode 9/23/2011 15. Performance relative to reference commercial solar cell 9/23/2011 16. Responsivity of Hamamatsu Photo-detector 9/23/2011 Fig b) Responsivity curve by Hamamatsu Fig a) Responsivity curve experimentallyobtained 17. What can we learn, what do we need to do to improve our EQE?9/23/2011
- Optimization of layer thickness(LT) of solar cells.
- Increase in LT increases absorption of photons but
- can reduce the mobility of charge carriers.
- Controlling the active layer growth rate results in an
- increased hole mobility and balanced charge transport
- Reduce degradation rate in performance of solar cell
- by amount of PCBM in layer