Department of Chemistry and Graduate Center for Materials Research , Missouri University of Science and Technology , Rolla , Missouri 65409-1170 , United States.
ACS Appl Mater Interfaces. 2018 Jun 27;10(25):21365-21371. doi: 10.1021/acsami.8b06388. Epub 2018 Jun 12.
An ultrathin, epitaxial Au layer was electrochemically deposited on n-Si(111) to form a Schottky junction that was used as the photoanode in a regenerative photoelectrochemical cell. Au serves as a semitransparent contact that both stabilizes n-Si against photopassivation and catalyzes the oxidation of Fe to Fe. In this cell, Fe was oxidized at the n-Si(111)/Au(111) photoanode and Fe was reduced at the Au cathode, leading to the conversion of solar energy into electrical energy with no net chemical reaction. The photocurrent was limited to 11.9 mA·cm because of the absorption of light by the Fe redox couple. When a transparent solution of sulfite ion was oxidized at the photoanode, photocurrent densities as high as 28.5 mA·cm were observed with AM 1.5 light of 100 mW·cm intensity. One goal of the work was to determine the effect of the Au layer on the interfacial energetics as a function of the Au coverage. There was a decrease in the barrier height from 0.81 to 0.73 eV as the gold coverage was increased from island growth with 10% coverage to a dense Au film with a thickness of 11 nm. In all cases, the band-bending in n-Si was induced by the n-Si/Au Schottky junction instead of the energetic mismatch between the Fermi level of n-Si and the redox couple. The dense Au film gave the greatest stability. Although the photocurrent of the n-Si/Au photoanode with 10.2% island coverage dropped nearly to zero within 2 h, the photocurrent of the photoanode with a dense 11 nm thick Au film only decreased to 92% of its initial value after irradiation at open circuit with AM 1.5 light for 16 h. A 2.1 nm thick layer of SiO formed between the Au film and n-Si. With further irradiation, the fill factor decreased because of the increase of series resistance as the SiO layer thickness exceeded tunneling dimensions.
在 n-Si(111)上电化学沉积一层超薄的外延 Au 层，形成肖特基结，用作再生光电化学电池的光阳极。Au 用作半透明接触，既能稳定 n-Si 防止光致钝化，又能催化 Fe 的氧化为 Fe。在该电池中，Fe 在 n-Si(111)/Au(111)光阳极处被氧化，而 Fe 在 Au 阴极处被还原，导致太阳能转化为电能，而无净化学反应。由于 Fe 氧化还原对吸收光，光电流限制在 11.9 mA·cm。当透明的亚硫酸根离子溶液在光阳极处被氧化时，在 100 mW·cm 强度的 AM 1.5 光下观察到高达 28.5 mA·cm 的光电流密度。该工作的一个目标是确定 Au 层对界面能的影响，作为 Au 覆盖率的函数。随着 Au 覆盖率从 10%岛状生长增加到 11 nm 厚的致密 Au 膜，势垒高度从 0.81 降低到 0.73 eV。在所有情况下，n-Si 的能带弯曲都是由 n-Si/Au 肖特基结引起的，而不是 n-Si 的费米能级与氧化还原对之间的能量失配引起的。致密的 Au 膜提供了最大的稳定性。尽管具有 10.2%岛状覆盖率的 n-Si/Au 光阳极的光电流在 2 小时内几乎降至零，但在 AM 1.5 光下开路照射 16 小时后，具有致密 11 nm 厚 Au 膜的光阳极的光电流仅降至初始值的 92%。在 Au 膜和 n-Si 之间形成了 2.1 nm 厚的 SiO 层。随着进一步的辐照，由于 SiO 层厚度超过隧道尺寸导致串联电阻增加，填充因子减小。
