AsianScientist (Nov. 3, 2015) – A research team led by Dr. Han Liyuan, director of the Photovoltaic Materials Unit at Japan’s National Institute for Materials Science, has developed the world’s first method to fabricate high-quality perovskite materials capable of utilizing long-wavelength sunlight of 800 nm or longer.
Compared to conventional methods, this method enables the creation of perovskite materials that have a 40-nm wider optical absorption spectrum, a high short-circuit current and high open-circuit voltage. Thus, this method is regarded as a new approach to enhance the efficiency of perovskite solar cells. This work was published in the journal, Advanced Materials.
Current perovskite solar cells possess optical absorption spectra skewed toward shorter wavelengths. To improve the energy conversion efficiency of these cells, it is vital to develop perovskite materials with optical absorption spectra expanded to include longer wavelengths.
To develop longer wavelength perovskite materials, researchers have used (MA)xFA1-xPbI3, which include two types of cations capable of absorbing light in the longer wavelength region. However, these cations have demerits: their mixing ratio and crystallization temperature are difficult to control. Moreover, due to their tendency to form a mixed crystal phase, there had been no effective method established to fabricate high-purity, single-crystalline perovskite materials.
To resolve these issues, the team developed a new method to fabricate a new type of mixed cation-based perovskite material. They first fabricated a pure, single-crystalline precursor material, (FAI)1-xPbI2, under altering temperatures. Then, they performed a reaction between the precursor and methylammonium iodide.
The resulting perovskite material, (MA)xFA1-xPbI3, was a single crystalline phase and had a long fluorescence lifetime. These observations indicated that electrons in the material rarely recombine and they have long lifetimes.
The optical absorption spectrum of the solar cells made from this material covered up to 840 nm, which was 40 nm wider than the spectrum of conventional perovskite material (MA3PbI3). As a result, the solar cells they developed obtained 1.4 mA/cm2 higher short-circuit current than the MAPbI3 solar cells that were manufactured under the same conditions.
In future studies, the team intends to develop high-quality perovskite solar cells capable of utilizing a broader spectrum of sunlight by adjusting the ratio of the two cations.
The article can be found at: Liu et al. (2015) High-Quality Mixed-Organic-Cation Perovskites from a Phase-Pure Non-stoichiometric Intermediate (FAI)1−x-PbI2 for Solar Cells.
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Source: National Institute for Materials Science.
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