Back-surface electric field passivation of CdTe solar cells using sputter-deposited CdSe

Abstract

CdTe back-surface passivation is one of the effective ways to enhance device performance. In recent years, the role of Se passivation in high performance CdSeTe thin film solar cell device has received increasing attention. However, current high-efficiency devices only have a considerable concentration of Se at the very front of the device, while most of the area on the back side of the absorber layer is not passivated by Se. This means that further efficiency improvements may be possible if more defects on the back surface of the absorber layer are passivated by Se, while maintaining the built-in field. Here, based on the magnetron sputtering process, chemical passivation and electric field passivation can be achieved when a small amount of CdSe is deposited on the CdTe back surface. When the CdSe thickness is ∼20 nm (Before annealing), the optimal cell current was increased from 23.8 mA/cm2 to 26 mA/cm2 and the efficiency was increased from 13.1% to 15.5%. External quantum efficiency and impedance spectroscopy measurements indicate that the performance improvement is due to the reduction of the interfacial recombination current on the back surface.