Performance improvement in CdTe solar cells by modifying the CdS/CdTe interface with a Cd treatment

• CdTe solar cells are often degraded.
• The diffusion of Cu from a Cu back contact to a CdS window layer.
• A Cd treatment at the CdS/CdTe interface.
• A dense CdS/CdTe interface and suppressed the intermixing of Te and S at the CdS/CdTe interface.
• The Cu diffusion from p-CdTe to CdS was suppressed, and the stability of the CdTe solar cell was greatly improved.

The performance of n-CdS/p-CdTe solar cells is often degraded under light soaking or thermal stress, even though the technology of CdTe solar cells is close to a commercial level. The Cu diffusion from a Cu back contact to a CdS window layer might degrade the cell's performance. To prevent the Cu diffusion, a very-thin intrinsic CdTe layer was introduced at the n-CdS/p-CdTe interface by depositing a very-thin Cd metal layer on the CdS film and converting the Cd metal into intrinsic CdTe during p-CdTe deposition at high temperature. By the Cd treatment on CdS surface, pinholes or voids were eliminated at the CdS/CdTe and the intermixing of Te and S at the interface was much suppressed. The depletion width was much increased and the intensity of LTPL peak was increased. The analysis suggested that an intrinsic CdTe interlayer was formed and the surface recombination rate was suppressed by the intrinsic interlayer. As a result, the short circuit current of the CdTe solar cell was significantly increased due the increased current gain in the blue wavelength region. The thermal stability of the CdTe solar cell was also greatly improved and the Cu diffusion was retarded by the intrinsic CdTe interlayer at the n-CdS/p-CdTe.