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-π-acceptor organic dye. While optimal device performance was achieved after 3-10 ALD cycles, 15 ALD cycles (∼2 Å of In2O 3) was observed to be optimal for increasing open-circuit voltage (VOC) with an average improvement of over 100 mV, including one device with an extremely high VOC of 1.00 V. An unexpected phenomenon was observed after 15 ALD cycles: the increasing VOC trend reversed, and after 30 ALD cycles VOC 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 VOC 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 TiO 2 conduction band, and mid-bandgap states introduced by In 2O3 accelerate recombination, leading to a reduced V OC. © 2013 American Chemical Society.
KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-015-21
Acknowledgements: This publication was based on work supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST). The development of the ALD reactor and ALD process was funded as part of the Center on Nanostructuring for Efficient Energy Conversion at Stanford University, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0001060. T.P.B. thanks the Albion Walter Hewlett Fellowship for financial support. J.T.T. gratefully acknowledges the Academy of Finland (Grant 256800/2012) and the Finnish Cultural Foundation for financial support. The authors thank Colin Bailie and Dr. George Margulis for advice in constructing the transient photovoltage/photocurrent setup and Dr. Chaiya Prasittichai for helpful discussions.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.