Some thoughts and suggestions on measuring Solar Cell I-V characteristics.
- Current and voltage sensors - A typical Si solar cell will have an open-circuit voltage(Voc) of between 0.55 - 0.65 volts. An A/D of one volt will work fine for measuring Voc. Typical currents will be around 25 - 35 mA/cm^2. Current varies directly with irradiance, so a 100 cm^2 cell will have a Short-Circuit current(Isc) of about 2.5 - 3.0 amps. Using a resistor across the cell and measuring the voltage across the resistor and calculating the current means you can have an A/D to measure voltages and don't need to measure the current directly. You can't measure Isc directly this way because you can never get to 0 volts. You would have to extrapolate to 0. There are other ways to measure the current, but they are usually very expensive.
- Temperature sensor - A thermistor, thermocouple, platinum RTD can be used. Voc is very sensitive to temperature, about 3 mV/deg C loss for a Silicon cell.
- Irradiance sensor - A calibrated reference cell is usually used to measure the irradiance of the light source. In your case a cell of the same type as those tested with a small resistor across it to measure the Isc should suffice. You would set the irradiance with the reference cell and then put the test cell under the light source and test it. This way you could compare difference cells under the same irradiance. Using the same type of cell means you don't have a spectral mismatch between the test cell and the reference cell.
- Light source - You will need a light source that is DC controlled or you will have a lot of 60 cycle problems.
If you have any specific questions I can try to answer them.
There is a lot of information on the internet on solar cell WWW.NREL.Gov is a good source. I've attached a file by Keith Emery of NREL on Solar Simulators and I-V measurements. It's probably got more information than you need but it is a good source.
Thanks
