Empa results published in Nature Materials
How to produce flexible CIGS solar cells with record efficiency
The technology yielding flexible solar cells with an 18.7% world record efficiency developed by scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, has now been published in “Nature Materials”. Key to the breakthrough is the control of the energy band gap grading in the copper indium gallium (di)selenide semiconductor, also known as CIGS, the layer that absorbs light and converts it into electricity.
Flexible CIGS solar cells developed at Empa.
High-performance flexible and lightweight solar cells, say, on plastic foils, have excellent potential to lower the manufacturing costs through roll-to-roll processing and the so called “balance-of-system” cost, thus enabling affordable solar electricity in the near future. Thus far, however, flexible solar cells on polymer films have been lacking behind in performance compared to rigid cells, primarily because polymer films require much lower temperatures during deposition of the absorber layer, generally resulting in much lower efficiencies.
Improvement in energy conversion efficiency of flexible CIGS solar cells on polymer film lead to the world record efficiency of 18.7% for flexible CIGS solar cells developed at Empa.
|“To achieve such high efficiency values, we had to reduce the recombination losses of photo-generated charge carriers”, said Tiwari. CIGS layers grown by co-evaporation at temperature of around 450 °C have a strong composition grading because of inadequate inter-diffusion of intermediate phases and preferential diffusion of gallium (Ga) towards the electrical back contact |
To overcome this problem doctoral students Adrian Chirilã and Patrick Bloesch developed novel processes for optimizing the solar cell performance. To achieve an appropriate composition profile in the CIGS layer – for enabling more efficient charge carrier collection and reduced interface recombination – Chirilã and colleagues developed an innovative growth process by carefully controlling the Ga and indium (In) evaporation flux during different stages of the evaporation process.