1. 1 Ken Hanson MWF 9:00 – 9:50 am Office Hours MWF 10:00-11:00 CHM 5175: Part 2.9 Solar Cell Operation and Characterization Source h Sample Multimeter

2. Increased Energy Demand International Energy Outlook (2010) Peak Oil Global Warming Projected Temperatures for 2090-2100 Pollution Why Solar?

3. ~750,000 BC 1903 1969 66 years 1896 2013 114 years 1977 2007 30 years 750,000 years

4. Human Energy Consumption C x H y = gasoline, wood, coal, methane, propane, acetylene… Biomass Coal Oil Gas Other

5. Fuel Solar Cell

6. Solar Energy vs. Consumption

7. The Power of Photons http://www.youtube.com/watch?v=8tt7RG3UR4c&t=1m23s http://www.youtube.com/watch?v=z0_nuvPKIi8

8. Solar ThermalSolar Photovoltaic (PV) Harvesting Solar Energy

9. Solar Thermal Energy

10. Solar collector for heating water A home in California in 1906 Solar Thermal Energy

12. Solar Oven Solar Water Purifier

13. Solar ThermalSolar Photovoltaic (PV) Harvesting Solar Energy

14. Photovoltaic “Photo” = light “voltaic” = electricity photovoltaic V = voltage I = current Load = light, battery fan (resistor) Earliest recorded use of “photovoltaic” was in 1849. h

15. Types of Photovoltaics

16. TiO 2 CAT D D h e-e- e-e- I3-I3- I-I- I-I- I3-I3- e-e- Dye-sensitized Solid-state Steps: 1) Light Absorption (Exciton transfer in organics) 2) Charge Separation 3) Hole and electron transport 4) Power Collection Organic

17. h C Load MO 2 CB VB Pt Dye-sensitized Solar Cells

18. I-I- h I3-I3- C e-e- I3-I3- I-I- Load MO 2 CB VB Pt e-e- Solar Energy into Electrical Energy Dye-sensitized Solar Cells

19. Gratzel et al. J. Chem. Ed. 1998, 75, 752. What you Need: FTO slides TiO 2 powder I - /I 2 solution Soft graphite pencil Dye -Raspberry -Blackberry -Green leaf multimeter $45 TiO 2 CAT D D h e-e- e-e- I3-I3- I-I- I-I- I3-I3- e-e- Institute for Chemical Education Build Your Own DSSC

20. I DSSC V Multimeter Variable Load V OC = 0.4 V I SC = 4-10 mA η = 0.5-1% Characterization

21. I current dark V oc voltage V P max I sc I max V max light Testing Station (CSL5303)

22. V = I x R Ohm’s Law V = Voltage I = Current R = Resistance I-V Curves P = I x V Electric Power (P)

23. Sequence of Events 1) Hook up electrodes 2) Measure current and voltage (no light) 3) Turn on light source 4) Measure current and voltage 5) Plot current vs. voltage I-V Curves

24. Open Circuit Voltage (V OC ): The voltage as the terminals are isolated (or with infinite load resistance). Short Circuit Current (I SC ): The current drawn as the terminals are connected (or with zero load resistance). Characterization : V oc I sc I-V Curves

25. Characterization: V OC : Open Circuit Voltage I SC : Short circuit current P max : Power Maximum V oc I sc P max P = I x V Electric Power (P) I-V Curves P max Efficiency (η) = P inc P inc : incident power How do we define P inc ?

26. Standardizing the Sun

28. Committee Internationale d'Eclaraige (CIE) and the American Society for Testing and Materials (ASTM) One air mass, or AM1 = the thickness of the Earth's atmosphere. Takes into account humidity, CO 2, N 2, ozone, etc.

29. AM1.5 = 1,000W/m 2 or 100 mW/cm 2 AM1.5 Solar Spectrum AM0 AM1.5

30. Filter Xenon Lamp Solar Simulator AM1.5 Filter AM1.5 Solar Spectrum

31. h Solar Cell Multimeter V oc I sc Characterization Characterization: V OC : Open Circuit Voltage I SC : Short circuit current P max : Power Maximum P inc : AM1.5 (100 mW/cm 2 ) P max Efficiency (η) = P inc AM1.5 Filter

32. V oc I sc I max V max P max η = P max /P inc FF = P max /(V OC x I sc ) FF = (I max x V max )/(V OC x I sc ) V OC : Open Circuit Voltage I SC : Short circuit current P max : Power Maximum V max : Max Power Voltage I max : Max Power Current FF : Fill Factor Fill Factor Fill Factor (FF)= Ideality of a solar cell or “squareness” of the I-V curve “Ideal” Solar Cell

33. Parasitic Resistance One is in series (R S ) and one is in parallel (R sh ) with the cell. Variables that influence Fill Factor Shunt Resistance (R sh ): providing an alternative current path for the light-generated current Series Resistance (R s ): resistance of the cell material to current flow (Example: poor contacts)

34. Increasing Series Resistance Variables that influence Fill Factor Decreasing Shunt Resistance FF RsRs R sh η η http://pveducation.org/pvcdrom/solar-cell-operation/impact-of-both-resistances

35. V oc I sc I max V max P max Improving Solar Cells FF I sc V OC η η η V OC x I sc x FF P inc η =η = = P max

36. V OC x I sc x FF P inc η =η = = P max Efficiency vs. FF, I sc, V oc

37. h Solar Cell Multimeter AM1.5 Filter Wavelength Dependence Solar Simulator Absorption Spectra

38. Source White Light Prism or Grating Solar Cell Measure Current N3 Dye Absorption Spectra IPCE Incident photon-to-current efficiency

40. Gratzel et al. Science 2011, 334, 629. Y123 YD2-o-C8 Incident photon-to-current efficiency

41. TiO 2 CAT red D D e-e- e-e- I3-I3- I-I- I-I- I3-I3- e-e- 10 -11 s 10 -3 s 10 -6 s 10 -7 s e-e- 10 -2 s 10 -4 s How do we study these processes in a device? Electrochemical Impedance Spectroscopy Electron Transfer Rates

42. time (t) phase shift (  Frequency-domain Measurement I0I0 Emission lifetime Electrochemical Impedance

43. V = I x R Ohm’s Law If R is constant: V (+) then I (+) V (-) then I (-) V = Voltage I = Current R = Resistance Electrochemical Impedance Spectroscopy

44. Impedance (Z): Opposition to current flow change in response to a voltage change. time (t) phase shift (  Electrochemical Impedance Spectroscopy Oscillate Voltage Monitor Current Resistance (R): R = V I Impedance (Z): Z(t) = E(t) I(t) E(t) = voltage at time t

45. Impedance (Z): Opposition to current flow change in response to a voltage change. Voltage (E) as a function of time: E(t) = E 0 cos(ωt) time (t) E 0 = max amplitude of the voltage ω = radial frequency phase shift (  I(t) = I 0 cos(ωt +  ) I 0 = max amplitude of the current Current as a function of time: Using Eulers relationship it is possible to express the impedance as a complex function. Electrochemical Impedance Spectroscopy

46. The expression for Z(  ) is composed of a real part (Z’) and an imaginary part (Z’’). Change in ω: change in , Z’ and Z” Z’ Z’’ Nyquist plot Semicircle = time constant RC circuit Resistance contributes to Z’ Capacitance contributes to Z” Z(t) Electrochemical Impedance Spectroscopy

47. Pt I-I- I3-I3- TiO 2 e-e- I-I- I3-I3- I - Diffusion J. Phys. Chem. B 2005, 109, 14945-14953

48. Thickness Dependence Find: MO Diffusion Rates Recombination Rates Transport Resistance Diffusion Coefficients Electrochemical Impedance Spectroscopy

49. I current dark V oc voltage V P max I sc I max V max light Solar Cell Characterization

50. Any Questions? Solar Cell Characterization