A tri-national team (Singapore-Israel-Switzerland) that includes two BGU professors has reported a major advance in the physics of perovskite solar cells – a new class of inorganic-organic hybrid materials that is spawning a revolution in photovoltaic technology.
“Perovskite” refers to a specific type of crystal structure, originally identified by the 19th century Russian mineralogist L.A. Perovski, but which remained unrecognized as a promising solar cell material until 2009. In the most rapid set of advances in the history of photovoltaic technology, cell efficiencies rose from 3% for the initial devices, to over 20% by 2015 – rivaling the performance of the best silicon solar cells. Perovskite cells are not only relatively simple to fabricate and far less expensive than silicon, but can be processed at temperatures 1000°C below those required for silicon.
In an example of experiment informing theory, impressive improvements in the efficiency of perovskite photovoltaics are not yet fully understood. In their recent article in the premier journal Advanced Materials, Prof. Jeffrey M. Gordon and Prof. Eugene A. Katz, both from the Alexandre Yersin Department of Solar Energy and Environmental Physics (YDSEEP) at the Jacob Blaustein Institutes for Desert Research, and colleagues used a combination of experiments that independently and expansively varied the intensity of incident light and cell temperature, toward elucidating the molecular mechanisms that permit these solar cells to exhibit surprisingly high voltage (more than 1.0 Volt per cell at ambient temperatures), while maintaining high current density and low internal resistive losses, which are essential for their superior performance.
Unlike basically all other photovoltaic devices where efficiency worsens as temperature rises, the research team produced high-performance cells where efficiency actually improves as the cells heat up, at common outdoor temperatures. The data are supported by the team’s new explanations for the underlying physical mechanisms, which also dispel previous erroneous published hypotheses. These findings also augur well for deploying perovskite solar cells under concentrated sunlight toward realizing yet higher efficiency – one of the next tasks in their planned experimental studies.
The research team was comprised of Wei-Lin Leong and Zi-En Ooi, from the Institute of Materials Research and Engineering, Singapore, Dharani Sabba and Nripan Mathews, from Nanyang Technological University, Singapore and Chenyi Yi, Shaik M. Zakeeruddin and Michael Graetzel, from Ecole Polytechnique Fédérale de Lausanne, Switzerland.
Above: Schematic diagram and electron micrograph of the architecture of the perovskite solar cells fabricated and studied experimentally. “FTO” refers to the transparent coating of Fluorine-doped Tin Oxide upon which incident sunlight impinges. The 100-nanometer scale bar highlights how exceptionally thin the solar cell can be. This is a consequence of the combination of the high solar absorptance of the perovskite layer and the excellent selective charge transport via the opposing layers of titanium dioxide, and an organic charge-transfer layer (Spiro-OMeTAD) that interfaces to the gold electrode.: Schematic diagram and electron micrograph of the architecture of the perovskite solar cells fabricated and studied experimentally. “FTO” refers to the transparent coating of Fluorine-doped Tin Oxide upon which incident sunlight impinges. The 100-nanometer scale bar highlights how exceptionally thin the solar cell can be. This is a consequence of the combination of the high solar absorptance of the perovskite layer and the excellent selective charge transport via the opposing layers of titanium dioxide, and an organic charge-transfer layer (Spiro-OMeTAD) that interfaces to the gold electrode.
