High Water-Splitting Efficiency through Intentional In and Sn Codoping in Hematite Photoanodes

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• 作者：Ali Kaouk ; Tero-Petri Ruoko ; Myeongwhun Pyeon ; Yakup GönüllüKimmo Kaunisto ; Helge Lemmetyinen ; Sanjay Mathur
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 15, 2016
• 年：2016
• 卷：120
• 期：49
• 页码：28345-28353
• 全文大小：623K
• ISSN：1932-7455

文摘

The effects of intermittent thin ITO layers on the water-splitting efficiency of α-Fe₂O₃ films grown by PECVD on FTO substrates are reported. The α-Fe₂O₃ was codoped with indium and tin by temperature-driven ionic transport and diffusion from the ultrathin ITO layer sputtered between the α-Fe₂O₃ layer and FTO substrate. The α-Fe₂O₃/ITO/FTO photoanodes showed a remarkable interdependence between the thickness of the ITO layer and PEC efficiency. Hematite photoanodes with a 32 nm thick ITO underlayer showed the highest photocurrent density of 2.5 mA cm^–2, corresponding to an approximate 3-fold enhancement over pristine α-Fe₂O₃ at 1.23 V vs RHE, whereas the thinner (8 nm) ITO underlayer yielded the lowest onset potential at 0.6 V vs RHE. Although the electrode with a thicker 72 nm ITO underlayer showed a higher onset potential of 0.9 V vs RHE, it still showed an enhancement in the photocurrent density at higher bias voltages. α-Fe₂O₃ was also deposited on metallic titanium substrates with intermittent sputtered tin and ITO layers. The codoping with indium and tin from ITO was observed to yield greatly enhanced performance when compared with both α-Fe₂O₃ alone and tin-doped α-Fe₂O₃. Transient absorption decays in the sub-nanosecond time scale were not affected by the doping, indicating that the doping had little effect on the primary charge carrier generation and recombination. On the other hand, fewer trapped electrons on the microsecond to millisecond time scale and a greatly increased amount of long-lived surface photoholes were observed for the ITO-doped samples. The transient absorption results imply that the large increases in photoelectrochemical efficiency were obtained due to higher electron mobility, which reduces recombination and leads to more efficient electron extraction from the electrodes.