How to make a solar cell (DIY/homemade solar cell) using a 2N3055 power transistor

To easily make a homemade/DIY solar cell, get a power transistor like the 2N3055 and carefully cut open the case. That exposes the semiconductor material inside to light. Hook up some wires and you're done! Doing this I managed to get around 500 millivolts and 5.5 milliamps which is 2.7 milliwatts. To power a 15 watt compact fluorescent lightbulb I'd need at least 5555 of them. However, just 5 of them in series will power a small 1.5 volt calculator in good indoor lighting conditions.

Be sure to also check out the solar panel I made using multiple of these transistor solar cells for powering a calculator as well as this more powerful one enclosed in a box.

The transistor solar cell wired up...
2N3055 transistor homemade solar cell wired up outdoors in sunlight.
... and being tested.
The test setup for the 2N3055 transistor homemade solar cell.

In the photo on the left below is the transistor.

Use a hacksaw to cut off the front of the metal case as in the photo on the right. There are thin delicate wires inside so when you cut, do many short cuts all around the case being careful to not let the blade go deeply inside the case. Don't do just one cut all the way through.

The 2N3055 power transistor - top view.
The 2N3055 power transistor.
Cutting open the case.
Cutting open the case of a 2N3055 transistor to make a solar cell.

In the photo on the left, below the case has been cut all the way to the backing and the thin, delicate wires are completely unprotected. In the photo on the right only the front part of the case has been cut off, leaving a protective, cylindrical wall around the insides, giving some protection for the wires.

The solar cell and thin wires.
The semiconductor material (solar cell) and delicate thin wires
      for the base and emitter inside the 2N3055 power transistor.
Case cut to leave a protective wall.
The insides of the 2N3055 power transistor with the case cut
      to leave a tall protective wall.

As shown in the photo and illustration, there are three points to make electrical contact with in a transistor unlike with a typical solar cell.

Bottom view showing where to connect wires.
The 2N3055 power transistor electrical connections.
Comparison of transistor and typical solar cell.
Comparison of the semiconductor p-type and n-type layers in
      a transistor and a typical solar cell.

To know how to connect to the transistor to get the best output I set up a testing station where the transistor would be fixed firmly in place while I tried all the possible ways of connecting to it and measured the output for each way. The results are on the right, below. This was done indoors to get constant lighting conditions. Two cool white compact fluorescent lightbulbs were used. This means that the values are low and may scale differently in sunlight since sunlight has a different range of frequencies.

Setup for testing the efficiency of the different ways of connecting.
The setup for testing the efficiency of the different ways of
      connecting to the 2n3055 transistor solar cell.
Test results
Test Voltage Current Power
Base+, Emitter- 370mV 94uA 35uW
Base & Emitter+, Collector- 325mV 215uA 70uW
Collector-, Base+ 340mV 265uA 90uW
Collector+, Emitter- 28mV 65uA 1uW

As you can see from the table above, using the Collector as negative (i.e. connecting to the metal case) and the Base as positive (i.e. connecting to the Base pin) while ignoring the Emitter gave the best results.

And lastly, for fun, I played around with focusing light on the solar cell using a small Fresnel lens to see the difference it made. I got around 520 millivolts and over 5.5 milliamps (measured on the microamps scale, the milliamps scale on my meter is broken.)

Focusing sunlight on the transistor solar cell using a Fresnel lens.
Focusing sunlight on the transistor solar cell using a small
    Fresnel lens.

Video all about the 2N3055 transistor solar cell

Here's a video I made about my experimenting with this 2N3055 transistor solar cell.

Making a solar panel from these transistor solar cells

Solar panel made of transistor solar cells for powering a
        calculator.

I made a solar panel using multiple of these transistor solar cells for powering a calculator.

Solar panel made of transistor solar cells enclosed in a 
        box.

More powerful solar panel using multiple of these transistor solar cells enclosed in a box.

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