Effects of the substrate temperature on the properties of CdTe thin films deposited by pulsed laser deposition

CdTe solar cells are not only CdS/CdTe p-n junction cells, but also a kind of multilayer thin films solar cells on Transparent-Conducting-Oxide (TCO) substrates. Many techniques can be employed to deposit CdTe films, such as close-spaced deposition (CSS), metal organic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). Among them, PLD is a promising and widely-used technique for multilayer thin films deposition. In general, the substrate temperature (Ts) is relatively low during PLD-CdTe thin films deposition processing in vacuum, less than 300 °C, which is not that high enough to fabricate high efficiency cells. It is firstly found by us that CdTe film can be deposited on higher temperature Fluorine-Tin-Oxide (FTO) substrates (≧ 400 °C) under a particular atmosphere by PLD. In this paper, the deposition of CdTe thin films at varying Ts in vacuum condition has been studied thoroughly and strong Ts dependence of the films properties has been revealed. Thus, based on this thorough study, by using the relatively high pressure and high Ts PLD technique, we fabricated an ultra-thin FTO/PLD-CdS(100 nm)/PLD-CdTe(~ 1.5 μm)/HgTe:Cu/Ag solar cell with an efficiency of 6.68% in the atmosphere of Ar + O2 (15 Torr) and at the relatively high Ts (500 °C).

► CdTe at200 °C, 400 °C and 550 °C have an average grain size of 30 nm, 300 nm and 500 nm, respectively.
► UnderAr:O2 atmosphere, CdTe films can be deposited a high Ts (≧ 400 °C) by PLD.
► An ultra-thin CdTe-based solar cell with an efficiency of 6.68% was fabricated.