Glass-ceramic covers for highly efficient solar cells
Glass-ceramic covers for highly efficient solar cells
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用于高效太阳能电池的玻璃陶瓷盖
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发表时间：
2010
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通讯作者：
Christian Pablick
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作者：
Christian Pablick
传统的单带隙太阳能电池无法利用整个太阳光谱。UV和IR波长区域是特别成问题的：IR光的能量低于典型半导体太阳能电池材料的带隙能量，而UV光谱范围中的光子能量的一部分通过载流子的热化和表面复合而被“浪费”。然而，频率“下移器”，如荧光玻璃和玻璃陶瓷掺杂稀土离子（例如，二价铕，Eu 2C），可以转换太阳光谱的高能量部分为可见光谱范围内的光子。降频描述了高能量光子的吸收和随后的具有较低能量的光子的发射，该光子可以被太阳能电池更有效地吸收。Eu 2C掺杂的氟锆酸盐（FZ）基玻璃陶瓷具有适合此目的的光学性能。它们可以在UV光谱范围内被激发，导致在蓝色光谱范围内发射。这里，转换效率主要取决于主体材料的声子能量（晶格振动）。基于FZ的玻璃因其低声子能量而众所周知，因此是作为降频器的理想主体。它们基于一种改性的玻璃系统，即所谓的ZBLAN，它是由锆（Zr）、钡（Ba）、镧（La）、铝（Al）和钠（Na）氟化物的混合物制成的玻璃的缩写。在我们的情况下，它们另外掺杂有氯离子，以使氯化钡（BaCl 2）纳米颗粒能够在热处理（退火）时生长，其中掺入Eu 2C。在260 ~ 280 ℃退火20 min，BaCl_2由六方相转变为正交相。(The后者描述了一种结晶系统，其特征是三个不相等的轴彼此成直角。在290 ℃的温度下，只有正交相BaCl 2如图1所示。氯化钡（BaCl 2）颗粒尺寸与退火温度的关系，用于5mol%（摩尔百分比）铕（Eu）掺杂的玻璃陶瓷。插图显示了在UV激发（280 nm）下，含有六方相（实线）和正交相（虚线）BaCl 2纳米晶体的玻璃陶瓷的Eu 2C荧光光谱。
A conventional mono-bandgap solar cell cannot take advantage of the entire solar spectrum. The UVand IR-wavelength regions are particularly problematic: the energy of IR light is lower than the bandgap energy of typical semiconductor solar-cell material, while a part of the photon energy in the UV spectral range is ‘wasted’ by thermalization and surface recombination of charge carriers. However, frequency ‘downshifters,’ such as fluorescent glasses and glass ceramics doped with rare-earth ions (for example, divalent europium, Eu2C), can convert the high-energy part of the solar spectrum into photons in the visible spectral range. Downshifting describes the absorption of a high-energy photon and the subsequent emission of a photon with lower energy that can be absorbed more efficiently by a solar cell. Eu2Cdoped fluorozirconate (FZ)-based glass ceramics have suitable optical properties for this purpose. They can be excited in the UV spectral range, leading to emission in the blue spectral regime. Here, the conversion efficiency depends mainly on the host material’s phonon energy (lattice vibrations). FZ-based glasses are well known for their low phonon energies and, therefore, are desirable hosts as downshifters. They are based on a modified glass system, so-called ZBLAN, which is an abbreviation for glasses made of a mixture of zirconium (Zr), barium (Ba), lanthanum (La), aluminum (Al), and sodium (Na) fluorides. In our case, they are additionally doped with chlorine ions to enable the growth of barium chloride (BaCl2) nanoparticles upon thermal treatment (annealing) in which the Eu2C is incorporated. Annealing for 20min at temperatures between 260 and 280C leads to a phase transformation from hexagonal to orthorhombic BaCl2. (The latter describes a system of crystallization characterized by three unequal axes at right angles to each other.) At a temperature of 290C only orthorhombic-phase BaCl2 is Figure 1. Barium chloride (BaCl2) particle size versus annealing temperature for a 5mol% (mole percent) europium (Eu)-doped glass ceramic. The inset shows Eu2C fluorescence spectra for glass ceramics containing hexagonal(solid) and orthorhombic-phase (dashed) BaCl2 nanocrystals under UV excitation (280nm).