Potential of CdZnTe Thin Film Back Buffer Layer for CdTe Solar Cells

Cadmium zinc telluride (CdZnTe, CZT) thin films were investigated for use as a back buffer layer in CdTe devices. We show that the CZT film is easily doped with copper (Cu). Devices with CZT:Cu/Au and CZT:Cu/Te/Au back contacts demonstrated significant gains in V-OC compared to Cu/Au back contacts. Barrier height measurements indicate that the valence band edge of the CZT is close to that of CdTe, which, when coupled with the high dopant density, should result in upward band bending at the back of the device. In the case of the CZT:Cu/Au back contact, the large band offset between the CZT and Au results in a depletion region that extends into the CdTe, limiting device performance. When the alignment is improved with the incorporation of Te, the efficiency improved.