The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
Nature. 2013 Nov 28;503(7477):509-12. doi: 10.1038/nature12622. Epub 2013 Nov 10.
Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p-n junction solar cell. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol-gel thin-film deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric-electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10(-4) to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7-4 electronvolts) of ferroelectric oxides, which allow the use of only 8-20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: [KNbO3]1 - x[BaNi1/2Nb1/2O3 - δ]x (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1-3.8 electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.
铁电体最近作为光伏器件的候选材料类别引起了人们的关注，因为它们可以将光吸收与其他功能特性结合起来。在这些材料中，由于自发极化引起的强反转对称性破缺促进了光激发载流子的理想分离，并允许电压高于带隙，这可能使效率超过传统 p-n 结太阳能电池的最大可能效率。铁电氧化物在广泛的机械、化学和热条件下也很稳定，并且可以使用溶胶-凝胶薄膜沉积和溅射等低成本方法制造。最近的工作表明，如何减小铁电层厚度并巧妙地设计畴结构和铁电电极界面，可以大大增加从铁电吸收材料中收集的电流，将功率转换效率从约 10(-4)提高到约 0.5%。铁电氧化物的宽带隙(2.7-4 电子伏特)限制了光伏效率的进一步提高，因为它只允许使用 8-20%的太阳光谱。在这里，我们描述了一种由低成本、无毒元素组成的单相固态氧化物固溶体家族：[KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x(KBNNO)。这些氧化物表现出铁电性和直接带隙在 1.1-3.8 电子伏特范围内的广泛变化。特别是，x=0.1 的组成在室温下是极性的，具有 1.39 电子伏特的直接带隙，并且光电流密度大约比经典铁电体(Pb，La)(Zr，Ti)O3 材料大 50 倍。KBNNO 能够吸收比当前铁电材料多 3 到 6 倍的太阳能，这表明了一种可行的基于铁电半导体的太阳能转换和其他应用的电池途径。
