High Quality CdS/CdTe P-N Junction Diode With a Noncontinuous Resistive SnO2 Buffer Layer

Abstract

In order to reduce light absorption of the n-type CdS window layer in high efficiency CdTe thin film solar cells, the window layer should be as thin as possible but enough thickness should be left to keep function of the p-n junction. However, many random shunting/shorting micropaths are unavoidably formed at the CdS/CdTe interface due to the CdS consumption up by the reaction/interdiffusion, or due to a noncontinuous coverage of CdS on transparent-conducting-oxide (TCO) thin films. These shunting/shorting paths are the main cause for the low open-circuit voltage and low efficiency of CdTe thin film solar cells. In this study, we propose to employ a noncontinuous highly resistive tin oxide (SnO2) layer between the TCO and the CdS window layer as an electronic shunting blocking layer. The experimental results demonstrated that the insertion of a noncontinuous SnO 2, which had a thickness of less than 10 nm, led to an enhancement in efficiency by 20% and an increase in open-circuit voltage ( $V_{{\rm{oc}}}$ ) by 14% compared to the one without SnO2. This study demonstrated an important design strategy for thin film solar cell fabrication to effectively reduce microshunting/shorting paths and to improve fabrication reproducibility of devices as well.