Plotting the IV Curve of a Solar Cell in EChem Software

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Revision as of 19:46, 10 July 2013 by Oliver (Talk | contribs) (Equipment Required)

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The eDAQ potentiostat and e-corder is used to plot the IV curve of a simple solar cell taken from a calculator
The EChem software will overlay IV curves collected under different conditions
A dye-sensitized solar cell

This application note describes a procedure for plotting the IV curve of a solar cell using eDAQ EChem software.

Introduction

The linear sweep voltammetry technique in EChem software can be used to plot the IV (current versus voltage) curve of a solar cell. The software can then overlay many IV curves recorded under different conditions. The EChem Startup System is an inexpensive, easy to use system for characterising solar cells.

Background

The development and testing of solar cells (and other power generation/storage devices such as batteries, capacitors, and fuel cells) requires characterisation of the performance of the device under different load conditions. In days gone by this was usually done by connecting an electrical resistor (which mimicked an actual load) to the device while the voltage and current were measured. This was repeated for different values of resistor over the range of interest, which could mean that many resistors would be required.

Ohm's Law tells us that current proportional to voltage divided by resistance, that is i = V/R, or put another way, if we know i and V than we can calculate R, R = V/i

Using a device called a potentiostat, we can control voltage and simultaneously measure the current. This means that a potentiostat can be used to characterise a solar cell by changing the potential across the cell and measuring the resulting current, and so can quickly determine the electrical characteristics for a large number of resistance values.

Equipment Required

The following equipment is required:

Procedure

To plot an IV curve in EChem software, start by determining the open circuit potential of the solar cell:

  1. Connect the electrodes cable of the potentiostat to the solar cell as follows: working electrode (green clip) on one side of the solar cell and reference electrode (yellow clip) on the other side. Do not connect the auxiliary electrode (red clip) to the solar cell at this time.
  2. Open the Chart software and use the High Z mode (High Impedance Voltmeter) of the potentiostat. Open the potentiostat window, select Mode = High Z, Range = 10 V and Cell = Real. The voltage can be read in the top left side of the window. This voltage is the open circuit potential of the solar cell, the voltage across the solar cell when no current is flowing. For more information on potentiostat operation please see the appropriate manual by using the links “EA163 EA362 EA164 Potentiostats” or "ER466 Potentiostat" after following the Manuals link at the eDAQ support page.
  3. If you are using a potentiostat which doesn't have High Z mode, use either a pH meter in voltage mode, or a voltmeter, to measure the open circuit potential of the solar cell.
  4. Make a note of the open circuit potential and close the Chart software.
  5. Now connect the electrode cable of the potentiostat to the solar cell as follows: working electrode (green clip) on one side of the solar cell and auxiliary and reference electrodes (red and yellow clips) on the other side.
  6. Open the EChem software and in the Technique menu chose “Linear Sweep”.
  7. Select a voltage range which is higher than the open circuit potential. Enter the value of the open circuit potential in “Initial” and zero in “Final”.
  8. Chose an appropriate rate. Click View to see how long the sweep will take. Click OK.
  9. Click Start to perform a scan.
  10. Expand the y-axis (current) to see the maximum current recorded.
  11. Change the current range of the potentiostat; the range must be higher than the maximum current, otherwise you will lose data points.
  12. Click Start to repeat the scan using the new current range setting.
  13. Check to see if the current reaches zero in the bottom right of the IV curve; if the current is always positive and never reached zero, you must increase the “initial” value in the Linear sweep window; if the current falls a lot below zero, do the opposite by decreasing the “initial” value, as this may damage your solar cell.

Notes

  • You can copy and paste the voltage and current values, or the IV picture, into third party software using the Copy Special command in the Edit menu.
  • Transfer the voltage and current data of an IV curve to Excel and create new columns for resistance, R = V/i, and work, W = i  x V
  • Make a graph that shows i, R, and W versus V. Determine the conditions that provide for maximum work by the solar cell.
  • Use the Show Overlay command in the Display menu, to overlay the IV curves you have collected; if you would like to delete a scan, use the Cut command in the Edit Menu.