The study of oxygen concentration in the CdTe thin film prepared by vapor transport deposition for CdTe photovoltaic devices

Abstract

Polycrystalline CdTe thin films for CdTe solar cell devices are grown using vapor transport deposition (VTD) which is one of promising techniques to prepare CdTe thin film for high efficiency CdTe solar cells. However, few works report the study of the CdTe thin film growth by VTD so far. In this paper, the oxygen concentration is altered to be O2-free, 10, 20, 30, 40 and 50%. The morphology and crystallinity of as-deposited CdTe films are studied by X-ray diffraction and scanning electron microscopy. And the electrical properties for CdTe photovoltaic devices is investigated by current–voltage (J–V), capacitance voltage (C–V), and time-resolved photoluminescence spectroscopy (TRPL) measurements. The results show that a small amount of oxygen in the process has a positive impact on CdTe thin film quality because the oxygen incorporation could effectively change the grain size and make grain orientation more pronounced. The carrier concentration increases from 2.3 × 1013 to 7.5 × 1013 cm−3 when the oxygen concentration increases from 0 to 10%. The result of carrier lifetime also shows a positive correlation with oxygen concentration. A series of devices performance reveal the optimal technological conditions is under 10% oxygen partial pressure. The best small-area CdTe thin film solar cell is obtained with the conversion efficiency of 12.65% without back contact layer.