Co-sputtered Zn1−XSnXO buffer layers for CdTe thin film solar cells

Buffer layers are a key component of high efficiency CdTe thin film solar cells. They allow the CdS thickness to be reduced thus increasing the device J_sc without any associated losses in FF or V_oc. In this work the impact of Zn_1-xSn_xO (ZTO) buffer layers on device performance are examined. ZTO films having various Zn/Sn ratio were produced in a single deposition by co-sputtering from Zn and Sn targets in an O₂ atmosphere. A series of devices were then produced using CdTe layers deposited by close space sublimation and the impact of the buffer layers were assessed from JV data. Zn rich films (~85% Zn, ~15% Sn) were found to give higher device efficiency, η = 8.76 ± 0.43%, than Sn rich (~31% Zn, ~69% Sn) films, η = 6.76 ± 0.51%. ZTO buffer layers were generally found to be inferior to sputtered ZnO buffer layers but far superior to SnO₂ films. Contrary to previous work no evidence for ZTO/CdS intermixing was observed. Comparisons are made between this work and previous studies of ZTO buffer layers.