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Solar Cell problem

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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Joined: November 29th, 2010, 4:53 pm
Country: United States

Solar Cell problem

Post by nickapuzzo » November 29th, 2010, 5:09 pm

Hello there, I'm using a 2440 sourcemeter in 4 wire mode, and applying a voltage to a solar cell (for charachterization) and have a problem.

The problem is seen in both sweep mode, and in manual (static) voltage mode.

Applying voltages roughly in the range of -0.5V to +0.5V, the V-I trace of the cell showed an anomalous feature, so I scoped the signal with a high impedance probe, and can see a high frequency oscillation occurring.

The oscillation is a few tenths of a volt peak to peak, it's fairly sinusoidal, it changes frequency from about 10KHz to about 100KHz when I block the light path somewhat (imperfectly).

The oscillation is not seen when I disconnect the 2400, things look as expected.

The oscillation is not seen when I connect a simple resistive load across the 2400.

Hence, I'm guessing the output stage of the 2400 might be interacting with the reactive load (the solar cell must have significant capacitance), and somehow causing a resonance.

Any assistance is greatly appreciated!
[email protected]

Tom Sw
Keithley Applications
Keithley Applications
Posts: 78
Joined: May 9th, 2010, 12:38 pm
Country: United States

Re: Solar Cell problem

Post by Tom Sw » November 30th, 2010, 5:10 am

Unfortunately highly capacitive loads can cause SMU's to oscillate. The 24XX family is the least prone to this behavior, but it can happen. One way to verify if this is the problem is to source current and measure voltage. If the oscillation disappears than this was the problem. If that’s the case, you may not be able to get rid of the oscillation if the SMU is configured as a voltage source, but you can try fixing the source and measure ranges at various values to see if you can improve the situation.

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