TiO2 Conduction Band Modulation with In2O3 Recombination Barrier Layers in Solid-State Dye-Sensitized Solar Cells

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• 作者：Thomas P. Brennan ; Jukka T. Tanskanen ; Katherine E. Roelofs ; John W. F. To ; William H. Nguyen ; Jonathan R. Bakke ; I-Kang Ding ; Brian E. Hardin ; Alan Sellinger ; Michael D. McGehee ; Stacey F. Bent
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：November 21, 2013
• 年：2013
• 卷：117
• 期：46
• 页码：24138-24149
• 全文大小：520K
• 年卷期：v.117,no.46(November 21, 2013)
• ISSN：1932-7455

文摘

Atomic layer deposition (ALD) was used to grow subnanometer indium oxide recombination barriers in a solid-state dye-sensitized solar cell (DSSC) based on the spiro-OMeTAD hole-transport material (HTM) and the WN1 donor-蟺-acceptor organic dye. While optimal device performance was achieved after 3鈥?0 ALD cycles, 15 ALD cycles (2 脜 of In₂O₃) was observed to be optimal for increasing open-circuit voltage (V_OC) with an average improvement of over 100 mV, including one device with an extremely high V_OC of 1.00 V. An unexpected phenomenon was observed after 15 ALD cycles: the increasing V_OC trend reversed, and after 30 ALD cycles V_OC dropped by over 100 mV relative to control devices without any In₂O₃. To explore possible causes of the nonmonotonic behavior resulting from In₂O₃ barrier layers, we conducted several device measurements, including transient photovoltage experiments and capacitance measurements, as well as density functional theory (DFT) studies. Our results suggest that the V_OC gains observed in the first 20 ALD cycles are due to both a surface dipole that pulls up the TiO₂ conduction band and recombination suppression. After 30 ALD cycles, however, both effects are reversed: the surface dipole of the In₂O₃ layer reverses direction, lowering the TiO₂ conduction band, and mid-bandgap states introduced by In₂O₃ accelerate recombination, leading to a reduced V_OC.