An efficiency of 12.4% has been reached with
flexible cadmium telluride (CdTe) thin-film solar cells by EMPA, the
Swiss Federal Laboratories for Materials Testing and Research in
Sponsors
Dubendorf, Switzerland.
The laboratory for thin Films and Photovoltaics
attached flexible CdTe thin-film solar cells on a lightweight polyimide
film by sing low temperatures (<450°C) vacuum evaporation process to
grow cadmium sulphide/cadmium telluride (CdS/CdTe) layers and a
subsequent annealing step in air where the materials are heated up and
cooled down to harden them.
The researchers used zinc oxide doped
on aluminium (ZnO:Al) as a transparent electric contact instead of the
expensive indium tin oxide (ITO) layer used in earlier 11.4% solar
cells.
In addition to being cheaper, the ZnO/ZnO:Al bi-layer
improved process yield and reproducibility of high efficiency solar
cells, EMPA says.
The
12.4% efficiency of the flexible thin-film solar cells was measured
under standard AMI.5 illumination condition. The parameters were Voc =
823 mV, Jsc = 19.6 mA.cm-2, FF = 76.5%.
EMPA says all the process
steps of the flexible thin-film solar cells are compatible with
continuous in-line processing and can be transferred to roll-to-roll
manufacturing of large area solar modules with high deposition speed.
“Such
high efficiency flexible CdTe solar cells can become a low cost option
for cost-effective solar electricity generation in near future,” EMPA
concludes.