Ravishankar Sandheep, Bisquert Juan, Kirchartz Thomas
IEK-5 Photovoltaik, Forschungszentrum Jülich 52425 Jülich Germany
Institute of Advanced Materials, Universitat Jaume I Castellón de la Plana 12071 Spain.
Chem Sci. 2022 Mar 31;13(17):4828-4837. doi: 10.1039/d1sc06401k. eCollection 2022 May 4.
A large body of literature reports that both bismuth vanadate and haematite photoanodes are semiconductors with an extremely high doping density between 10 and 10 cm. Such values are obtained from Mott-Schottky plots by assuming that the measured capacitance is dominated by the capacitance of the depletion layer formed by the doping density within the photoanode. In this work, we show that such an assumption is erroneous in many cases because the injection of electrons from the collecting contact creates a ubiquitous capacitance step that is very difficult to distinguish from that of the depletion layer. Based on this reasoning, we derive an analytical resolution limit that is independent of the assumed active area and surface roughness of the photoanode, below which doping densities cannot be measured in a capacitance measurement. We find that the reported doping densities in the literature lie very close to this value and therefore conclude that there is no credible evidence from capacitance measurements that confirms that bismuth vanadate and haematite photoanodes contain high doping densities.
大量文献报道，钒酸铋和赤铁矿光阳极都是半导体，其掺杂密度极高，在10¹⁰至10¹¹cm⁻³之间。这些值是通过莫特-肖特基曲线获得的，假设测量的电容由光阳极内掺杂密度形成的耗尽层电容主导。在这项工作中，我们表明这种假设在许多情况下是错误的，因为从收集接触注入电子会产生一个普遍存在的电容阶跃，很难与耗尽层的电容区分开来。基于此推理，我们得出了一个与光阳极假定的有效面积和表面粗糙度无关的解析分辨率极限，低于该极限，在电容测量中无法测量掺杂密度。我们发现文献中报道的掺杂密度非常接近这个值，因此得出结论，电容测量中没有可靠证据证实钒酸铋和赤铁矿光阳极含有高掺杂密度。
