Understanding what makes a thin film solar cell efficient

(Nanowerk News) For many years scientists and engineers have been trying to provide low-cost solar energy by developing a cheap solar cell that is both highly efficient and at the same time simple to build, enabling it to be mass produced. Now, the team led by Empa researcher Ayodhya N. Tiwari has made a major leap forward: the researchers are presenting a new manufacturing technique for CIGS solar cells, in which tiny quantities of sodium and potassium are incorporated into the CIGS layer. The special treatment alters the chemical composition of the complex sandwich structure  thereby altering its electronic properties, as confirmed by various methods including detailed electron microscope investigations.

Details of the new method have now been published as an "Advance Online Publication" in the renowned journal Nature Materials ("Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells").

This shows high efficiency, flexible CIGS solar cells on polyimide film developed using a new process.

With this technique, the Empa team has again been able to significantly increase the energy conversion efficiency from sunlight into electricity using CIGS thin film solar cells on flexible plastic foils  to a new record level of 20.4%, representing a marked improvement over the previous record of 18.7% established by the same team in May 2011. This finally enables CIGS cells to compete with the best polycrystalline silicon cells.