Ultrathin Buffer Layers of SnO2 by Atomic Layer Deposition: Perfect Blocking Function and Thermal Stability

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• 作者：Ladislav KavanLudmilla Steier ; Michael Grätzel
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 12, 2017
• 年：2017
• 卷：121
• 期：1
• 页码：342-350
• 全文大小：539K
• ISSN：1932-7455

文摘

This study pinpoints the advantages of ultrathin electron selective layers (ESL) of SnO₂ fabricated by atomic layer deposition (ALD). These layers recently caught attention in planar perovskite solar cells and appear as powerful alternatives to other oxides such as TiO₂. Here, we carry out a thorough characterization of the nature of these ultrathin ALD SnO₂ layers providing a novel physical insight for the design of various photoelectrodes in perovskite and dye-sensitized solar cells and in photoelectrochemical water splitting. We use a combination of cyclic voltammetry, electrochemical impedance spectroscopy, Hall measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and electron microscopy to analyze the blocking behavior and energetics of as-deposited (low-temperature) and also calcined ALD SnO₂ layers. First, we find that the low-temperature ALD-grown SnO₂ layers are amorphous and perfectly pinhole-free for thicknesses down to 2 nm. This exceptional blocking behavior of thin ALD SnO₂ layers allows photoelectrode designs with even thinner electron selective layers, thus potentially minimizing resistance losses. The compact nature and blocking function of thin SnO₂ films are not perturbed by annealing at 450 °C, which is a significant benefit compared to other amorphous ALD oxides. Further on, we show that amorphous and crystalline ALD SnO₂ films substantially differ in their flatband (and conduction band) positions—a finding to be taken into account when considering band alignment engineering in solar devices using these high-quality blocking layers.