Replacing the thin-film that is the most commonly used hole-transporting material in perovskite and dye-sensitized solar cells with a single-crystal version of the same material could increase its efficiency exponentially, according to research published this month in Science Advances.
In the study, Dong Shi from the Solar and Photovoltaics Engineering Research Center at King Abdullah University of Science and Technology in Saudi Arabia and his colleagues reported that the material, known as spiro-OMeTAD, has been used for nearly two decades, and many thought that its full potential had already been tapped, leading to the search for a replacement.
According to Phys.org, however, Shi’s team decided to take a second look at the substance and discovered that by growing single crystals of pure spiro-OMeTAD, they could create a layer with a hole mobility that was three orders of magnitude greater than the currently-used thin-film form. The discovery could delay the need for a replacement material, the study authors explained.
Osman Bakr, a professor of engineering who works alongside Shi at the university, called the work “a major breakthrough for the fields of perovskite and solid-state dye-sensitized solar cells” and told the website that it clarified “the potential performance of the material” by showing that “improving the crystallinity of the hole transport layer” was “key” to future breakthroughs.
Solving a 17-year-old mystery by crystallizing spiro-OMeTAD
Typically, solar cells are comprised of three essential layers. Two of them – one which transports electrons and one which absorbs light – have structures that are well-understood, but the third – a structure which contains the hole-transporting layer (usually spiro-OMeTAD) has long been a bit of a mystery to researchers, limiting their knowledge of its charge transport mechanisms.
However, as Phys.org reports, the authors of the new study discovered a way to dissolve spiro-OMeTAD in a vial using a solvent, then place that vial inside a larger vial that had been filled with an antisolvent. Since spiro-OMeTAD does not dissolve as well in the antisolvent the substance was able to slowly diffuse into the inner vial, eventually causing the solution inside the inner vial to become supersaturated and crystallize.
Shi’s team then made a series of measurements on the crystals to determine its charge transport mechanisms and other properties, the website said. The results were said to be encouraging, and suggests that spiro-OMeTAD may not yet have maxed out its usefulness in solar cells. The bad news, however, is that the technique used to grow single crystals of the substance cannot be used to mass-produce them, but the researchers are confident that they can find similar, alternate ways to achieve similar results.
“These astonishing findings open a new direction for the development of perovskite solar cells and dye-sensitized solar cells by showing the still untapped potential of spiro-OMeTAD,” Bakr told Phys.org. “They unravel a key mystery that has confounded the photovoltaic community for the last 17 years.”
Image credit: Thinkstock