Researchers from EMPA have improved the efficiency of flexible CdTe thin-film solar cells to 12.4% value.
The laboratory for Thin Films and Photovoltaics of EMPA, Switzerland has developed highest efficiency flexible CdTe thin-film solar cells on a lightweight polymer (polyimide) film by using a low temperature – below 450°C – vacuum evaporation process to grow CdS/CdTe layers and a subsequent annealing step in air.
This 12.4% device structure is the use of ZnO:Al as a transparent electrical contact instead of the expensive ITO (indium tin oxide) layer the company used earlier in 11.4% efficiency solar cells. Substitution of ITO with a bi-layer of ZnO/ZnO:Al also improved process yield and reproducibility of high efficiency solar cells. The photovoltaic parameters of the 12.4% efficiency solar cell measured under standard AM1.5 illumination condition are Voc= 823 mV, Jsc= 19.6 mA.cm-2, FF= 76.5%.
The research group has been involved in the development of CdTe solar cells on glass and polymer substrates for several years, developing low temperature and compatible processes and combating the reduction of optical and electronic losses limiting the cell performance.
All the process steps of the flexible 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 could become a low cost option for cost effective solar electricity generation in the near future, meaning another potential increase for the sector market.