Contents I. Introduction
Surface passivation plays a critical role for the fabrication of highly efficient solar cells. The front and back surfaces of the solar cells are the sources of high defect densities acting as a recombination centers, and thus reducing the photo-voltage and fill factor of the device. The back surface is more challenging in CdTe photovoltaics compared to the front surface due to the lack of good conducting passivating layer with appropriate band alignment to CdTe layer. At the same time, formation of ohmic contact by the use of p+ layer is essential to fabricate highly efficient devices. Previously, several materials such as aluminum oxide (Al2O3) have shown significant improvement in carrier lifetime of CdTe photovoltaics when utilized as a passivating layer. [1], [2] However, fabrication of efficient devices using Al2O3 requires that the alumina layer be doped to reduce its insulating qualities. More recently, solution processed copper aluminum oxide (CuxAlOy) as a back buffer layer to CdS/CdTe device have shown improvement in minority carrier lifetime.[3]
