Studies of Cu location near the back contact of CdS/CdTe solar cells

We have used the x-ray fluorescence signal from copper selectively excited with a ∼10 keV photon beam from the Argonne Advanced Photon Source to probe low levels of copper in sputtered CdTe cells. Through a peel-off technique that separates the evaporated Cu/Au back contact from the CdTe, we are able to determine where the Cu resides after cell preparation is finished. With a 3 to 4 nm Cu layer under the 20 nm of gold, we find that about 10% stays with the CdTe after contact peel-off. Recontacting these cells with fresh gold yields cell performance very close to the originally prepared contacts indicating that only 3–4 Å of copper is needed for a good contact that exhibits no rollover in the first quadrant of the I–V curve.