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A group of scientists at the Swiss Federal Institute of Technology Lausanne (EPFL) claims to have made a leap forward to improve the scalability of perovskite solar cells, by replacing their electron-transport layers with a thin layer of quantum dots.
So far, perovskite solar cells have proven to be extremely unstable when scaled up to mass production and the high efficiencies achieved in laboratories cannot be easily reproduced when transferred to production lines, the researchers said. This is partly due to the cell’s electron transport layer, which ensures that the electrons generated when the cell absorbs light are efficiently transferred to the device’s electrode.
In conventional perovskite solar cells, the electron transport layer (ETL) consists of mesoporous titanium dioxide, which has low electron mobility and is also susceptible to negative photocatalytic events under ultraviolet light.
The EPFL replaced the ETL with a thin layer of tin(IV) oxide quantum dots stabilised with polyacrylic acid. This improved the light-trapping capacity of the cells while suppressing non-radiative recombination.
With the thin layer of quantum dots, higher efficiencies can also be transferred to larger cell formats. According to the researchers, they achieved a record efficiency of 25.7% on a perovskite solar cell with an area of 0.08cm2. At the same time, high operational stability was demonstrated, which resulted in efficiencies of 23.3%, 21.7% and 20.6% when the surface of the solar cells was increased to 1cm2, 20cm2, and 64cm2.
Quantum dots are nanometer-sized particles that act as semiconductors and emit light of specific wavelengths when illuminated. Because of their unique optical properties, quantum dots are ideal for use in a variety of optical applications, including photovoltaics.
Colloidal quantum dot solar cells (QDSCs) have caught the eye of PV researchers of late thanks to their potential for high conversion efficiency and low-cost processing. However, the technology is still a long way from leaving the lab. Beyond efficiency there are a host of other conditions that need to be met before commercial production can be considered.