Michael Gratzel holding a DSSC (photo courtesy of EPFL)
Michael Gratzel holding a DSSC (photo courtesy of EPFL)
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Ecole Polytechnique Federale de Lausanne (EPFL), a Switzerland-based university, announced that a research team led by Michael Gratzel, a researcher at the university, developed a solid-state dye-sensitized solar cell (DSSC) with a conversion efficiency of 15%.

It was announced in a paper, etc. Before the development, the highest conversion efficiency of a DSSC was about 13%. And the 15% efficiency can be a significant advance for the full-scale commercialization of DSSC.

The DSSC uses an inorganic-organic composite material having a perovskite structure (e.g. CH3NH3PbI3) as a dye sensitizer and a hole transport material (HTM) consisting of organic materials in place of electrolyte. Specifically, it is a solid-state DSSC having a structure of glass/FTO/TiO2/CH3NH3PbI3/HTM/Au.

A DSSC with this structure was proposed by a research team led by Tsutomu Miyasaka, professor at Toin University of Yokohama, in 2009. At that time, its conversion efficiency was 3.8%. And, recently, EPFL developed a cell whose conversion efficiency is higher than 13%. However, there was a wide variation in the particle diameter of the perovskite-structured material formed on TiO2, causing a wide variation in performance.

This time, Gratzel and other researchers in the team accumulated a perovskite-structured material on TiO2 in two steps. Specifically, Pbl2 was accumulated on TiO2, and, then, it was immersed in a CH3NH3I solution. With this method, it became possible to make a DSSC having a high conversion efficiency with a high reproducibility, EPFL said.