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wiseroy

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[资源] 钙钛矿结构铁电材料-可见光波段光电效应-nature-2013

钙钛矿型氧化物铁电体的可见光波段光电研究
2013，nature-Perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials
关键词：铁电材料光伏效应可见光带隙
报道了能从入射光产生电流的一种氧化物。作为铁电材料特征之一的自发极化对于太阳能电池应用具有吸引力，因为由光吸收产生的正电荷和负电荷具有彼此分开的自然倾向，这使得它们更容易被高效收集。遗憾的是，大多数已知的铁电材料都有比较宽的禁带，即它们只吸收构成太阳光谱一小部分的高能光子。现在，宾夕法利亚大学化学系的安德鲁・阿姆等人发现，可以对一种经典的铁电材料进行化学改造，在大范围内调节其带隙，从而在整个太阳光谱上都能实现强吸收和光电流生成。
安德鲁?阿姆研究团队通过常规的固态方法，利用廉价和无毒性的元素制成了单相固体氧化物[KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x (KBNNO)。这类氧化物既具有铁电性质，还表现出了变化范围在1.1~3.8 eV的直接带隙。在x = 0.1下，KBNNO的光电流密度比经典的铁电体(Pb,La)(Zr,Ti)O3材料大约50倍，光吸收能力比目前的铁电体材料高3至6倍。此工作为研究基于铁电体半导体的太阳能电池开辟了一条新途径。

All samples weremade by standard solid-state synthesis techniques in the powder form, followed by sintering.An integrated focused ion beamand scanning electron microscope (FEI, DB235) equipped with a lift-out tool (Omniprobe) was used to extract thin-film lamellae from the bulk-synthesized KBNNO pellets for bandgap and local ferroelectric piezoelectric switching measurements. Mesoscopic (about 20 mm thick) samples were prepared by metallization of the polished side of each pellet using thermally evaporated layers of Cr (5 nm) and Au (100 nm), followed bymounting with the pellet’s metallized side face down, thinning and subsequent polishing to a root mean squared roughness of around 100 nm. Indium/tin oxide thin films (about 50 nm) were subsequently deposited onto shadow-masked, approximately 20-mm-thick KBNNO via pulsed laser deposition at 200 uCin O2. Bandgaps weremeasured by spectroscopic ellipsometry using a variable-angle spectroscopic ellipsometer equipped with Glan–Taylor polarizers, a rotating compensator, and deuterium and quartz halogen lamps for spectral coverage (J. A.Woollam, Model M2000). Ferroelectric switching within the lamellae was evaluated from the local piezoresponse using a scanning probe microscope (Asylum Research, MFP-3D) and Pt-coated Si probes (Olympus, AC 240TM; nominal stiffness constant, about 2Nm21). Ferroelectric polarization hysteresis measurements were collected at 77–200K in high vacuum (1027torr) and at ambient pressure using a ferroelectric tester (Radiant LC). Steady-state photocurrent/bias-voltage traces were collected in bulk KBNNOand BTO and in approximately 20-mm-thick films under 120-W tungsten–halogen spectrally broad lamp probe illumination and using a fibre-coupled supercontinuum source (NKT Compact), under vacuum (1026 torr, Lakeshore Cryotronics, TTP4) using a picoammeter (Keithley, model 6487). Photocurrent spectra were collected using a tunable wavelength Ti:sapphire laser (M2 SolsTiS)with an incident spot diameter of about 10mm. First-principles DFT LDA1U calculations were done using normconserving pseudopotentials and a plane-wave basis set, as implemented in the Quantum-Espresso package.[ Last edited by wiseroy on 2014-1-12 at 22:57 ]

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