Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells

Nga Phung (Corresponding author), Marcel Verheijen, Anna Todinova, Kunal Datta, Michael Verhage, Amran Al-Ashouri, Hans Köbler, Xin Li, Antonio Abate, Steve Albrecht, Mariadriana Creatore (Corresponding author)

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Abstract

Metal halide perovskites have attracted tremendous attention due to their excellent electronic properties. Recent advancements in device performance and stability of perovskite solar cells (PSCs) have been achieved with the application of self-assembled monolayers (SAMs), serving as stand-alone hole transport layers in the p-i-n architecture. Specifically, phosphonic acid SAMs, directly functionalizing indium-tin oxide (ITO), are presently adopted for highly efficient devices. Despite their successes, so far, little is known about the surface coverage of SAMs on ITO used in PSCs application, which can affect the device performance, as non-covered areas can result in shunting or low open-circuit voltage. In this study, we investigate the surface coverage of SAMs on ITO and observe that the SAM of MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid) inhomogeneously covers the ITO substrate. Instead, when adopting an intermediate layer of NiO between ITO and the SAM, the homogeneity, and hence the surface coverage of the SAM, improve. In this work, NiO is processed by plasma-assisted atomic layer deposition (ALD) with Ni(MeCp)2 as the precursor and O2 plasma as the co-reactant. Specifically, the presence of ALD NiO leads to a homogeneous distribution of SAM molecules on the metal oxide area, accompanied by a high shunt resistance in the devices with respect to those with SAM directly processed on ITO. At the same time, the SAM is key to the improvement of the open-circuit voltage of NiO + MeO-2PACz devices compared to those with NiO alone. Thus, the combination of NiO and SAM results in a narrower distribution of device performance reaching a more than 20% efficient champion device. The enhancement of SAM coverage in the presence of NiO is corroborated by several characterization techniques including advanced imaging by transmission electron microscopy (TEM), elemental composition quantification by Rutherford backscattering spectrometry (RBS), and conductive atomic force microscopy (c-AFM) mapping. We believe this finding will further promote the usage of phosphonic acid based SAM molecules in perovskite PV.

Original languageEnglish
Pages (from-to)2166-2176
Number of pages11
JournalACS Applied Materials and Interfaces
Volume14
Issue number1
DOIs
Publication statusPublished - 12 Jan 2022

Bibliographical note

Funding Information:
The authors acknowledge the technical support of Thomas Lußky, Hagen Heinz, Monika Gabernig, and Carola Ferber at HZB, Cristian van Helvoirt, Caspar van Bommel, Joris Meulendijks and Janneke Zeebregts at TU/e. The authors thank Wim Arnold-Bik at DIFFER for performing RBS measurement, Carola Klimm (HZB) for acquiring SEM images, and Dr. Beatriz Barcones Campo (TU/e) for preparing FIB for TEM measurement. N.P. thanks Dr. Ece Aktas (ICIQ), Dr. Artiom Magomedov (KTU), Dr. Gerben van Straaten (TU/e), Dr. Stephan Prünte (TU/e), and Kousumi Mukherjee (TU/e) for fruitful discussion. The authors are grateful to Prof. dr. René Janssen (TU/e) for the valuable discussions. N.P. and M. Verhage thank Ömür Gökçinar (TU/e) for his support during c-AFM measurements. Solliance and the Dutch province of Noord-Brabant are acknowledged for funding the TEM facility. A.A.A. and S. A. acknowledge the BMBF for funding of the Young Investigator Group (grant no. 03SF0540) within the project “Materialforschung fur die Energiewende.” A.T. and M.C. acknowledge the TKI Urban Energy (PVPress TEUE 118010). M.C. acknowledges the NWO Aspasia program.

Keywords

  • atomic layer deposition
  • indium tin oxide
  • nickel oxide
  • perovskite solar cells
  • self-assembled monolayer
  • surface coverage

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