InxGa1−xN is a promising material for flexible and efficient water-splitting photoelectrodes since the bandgap is tunable by modifying the indium content. We investigate the potential of an InxGa1−xN/Si tandem used as a water-splitting photoelectrode. We predict a maximum theoretical photogeneration efficiency of 27% for InxGa1−xN/Si tandem photoelectrodes by computing electromagnetic wave propagation and absorption. This maximum is obtained for an indium content between 50% and 60% (i.e., a bandgap between 1.4 eV and 1.2 eV, respectively) and a film thickness between 280 nm and 560 nm. We then experimentally assess InxGa1−xN photoanodes with the indium content varying between 9.5% and 41.4%. A Mott–Schottky analysis indicates doping concentrations (which effectively represent defect density, given there was no intentional doping) above 8.1 × 1020 cm−3 (with a maximum doping concentration of 1.9 × 1022 cm−3 for an indium content of 9.5%) and flatband potentials between −0.33 VRHE for x = 9.5% and −0.06 VRHE for x = 33.3%. Photocurrent–voltage curves of InxGa1−xN photoanodes are measured in 1M H2SO4 and 1M Na2SO4, and the incident photon-to-current efficiency spectra in 1M Na2SO4. The incident photon-to-current efficiency spectra are used to computationally determine the diffusion length, the diffusion optical number, as well as surface recombination and transfer currents. A maximum diffusion length of 262 nm is obtained for an indium content of 23.5%, in part resulting from the relatively low doping concentration (9.8 × 1020 cm−3 at x = 23.5%). Nevertheless, the relatively high surface roughness (rms of 7.2 nm) and low flatband potential (−0.1 VRHE) at x = 23.5% cause high surface recombination and affect negatively the overall photoelectrode performance. Thus, the performance of InxGa1−xN photoelectrodes appears to be a tradeoff between surface recombination (affected by surface roughness and flatband potential) and diffusion length (affected by doping concentration/defect density). The performance improvements of the InxGa1−xN photoanodes are most likely achieved through modification of the doping concentration (defect density) and reduction of the surface recombination (e.g., by the deposition of a passivation layer and co-catalysts). The investigations of the ability to reach high performance by nanostructuring indicate that reasonable improvements through nanostructuring might be very challenging.

中文翻译：

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InxGa1−xN/Si串联水分解光电极的理论最大光生效率和性能表征

InxGa1-xN 是一种很有前途的柔性和高效水分解光电极材料，因为带隙可通过改变铟含量进行调节。我们研究了 InxGa1−xN/Si 串联用作水分解光电极的潜力。通过计算电磁波的传播和吸收，我们预测 InxGa1-xN/Si 串联光电极的最大理论光生效率为 27%。该最大值是在铟含量介于 50% 和 60% 之间（即带隙分别介于 1.4 eV 和 1.2 eV 之间）和膜厚介于 280 nm 和 560 nm 之间时获得的。然后我们通过实验评估铟含量在 9.5% 到 41.4% 之间变化的 InxGa1-xN 光阳极。Mott-Schottky 分析表明掺杂浓度（在没有有意掺杂的情况下有效代表缺陷密度）高于 8。1 × 1020 cm-3（最大掺杂浓度为 1.9 × 1022 cm-3，铟含量为 9.5%），平带电位介于 -0.33 VRHE（x = 9.5%）和 -0.06 VRHE（x = 33.3%）之间。InxGa1−xN 光阳极的光电流-电压曲线在 1M H2SO4 和 1M Na2SO4 中测量，入射光子-电流效率谱在 1M Na2SO4 中测量。入射光子到电流效率谱用于计算确定扩散长度、扩散光学数以及表面复合和转移电流。对于 23.5% 的铟含量，获得 262 nm 的最大扩散长度，部分原因是掺杂浓度相对较低（9.8 × 1020 cm-3 at x = 23.5%）。然而，在 x = 23 处相对较高的表面粗糙度（7.2 nm 的 rms）和低平带电位（-0.1 VRHE）。5% 会导致高表面复合并对整体光电极性能产生负面影响。因此，InxGa1-xN 光电极的性能似乎是表面复合（受表面粗糙度和平带电位影响）和扩散长度（受掺杂浓度/缺陷密度影响）之间的权衡。InxGa1-xN 光阳极的性能改进最有可能通过改变掺杂浓度（缺陷密度）和减少表面复合（例如，通过沉积钝化层和助催化剂）来实现。通过纳米结构达到高性能的能力的研究表明，通过纳米结构进行合理的改进可能非常具有挑战性。InxGa1-xN 光电极的性能似乎是表面复合（受表面粗糙度和平带电位影响）和扩散长度（受掺杂浓度/缺陷密度影响）之间的权衡。InxGa1-xN 光阳极的性能改进最有可能通过改变掺杂浓度（缺陷密度）和减少表面复合（例如，通过沉积钝化层和助催化剂）来实现。通过纳米结构达到高性能的能力的研究表明，通过纳米结构进行合理的改进可能非常具有挑战性。InxGa1-xN 光电极的性能似乎是表面复合（受表面粗糙度和平带电位影响）和扩散长度（受掺杂浓度/缺陷密度影响）之间的权衡。InxGa1-xN 光阳极的性能改进最有可能通过改变掺杂浓度（缺陷密度）和减少表面复合（例如，通过沉积钝化层和助催化剂）来实现。通过纳米结构达到高性能的能力的研究表明，通过纳米结构进行合理的改进可能非常具有挑战性。InxGa1-xN 光阳极的性能改进最有可能通过改变掺杂浓度（缺陷密度）和减少表面复合（例如，通过沉积钝化层和助催化剂）来实现。通过纳米结构达到高性能的能力的研究表明，通过纳米结构进行合理的改进可能非常具有挑战性。InxGa1-xN 光阳极的性能改进最有可能通过改变掺杂浓度（缺陷密度）和减少表面复合（例如，通过沉积钝化层和助催化剂）来实现。通过纳米结构达到高性能的能力的研究表明，通过纳米结构进行合理的改进可能非常具有挑战性。