Combustion Synthesized NiCo2O4 Hole Transport Layer for Inverted Perovskite Solar Cells

Ioannis Papadas^a, Apostolos Ioakeimidis^a, Gerasimos Armatas^b, Stelios Choulis^a

^aCyprus University of Technology, Kitiou Kyprianou, 45, Limassol, Cyprus

^bDepartment of Materials Science and Technology, University of Crete, Heraklion, 710 03 Crete, Greece, Greece

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)

#PERFuDe19. Halide perovskites: when theory meets experiment from fundamentals to devices

Berlin, Germany, 2019 November 3rd - 8th

Organizers: Claudine Katan, Wolfgang Tress and Simone Meloni

Poster, Ioannis Papadas, 387
Publication date: 18th July 2019

In this work, we report the synthesis and characterization of a low-temperature solution-processable monodispersed nickel cobaltite (NiCo₂O₄) nanoparticles via a combustion method proposing tartaric acid as a fuel and nitrate as an oxidizer agent and demonstrate its performance as hole transport layer (HTL) for Perovskite Solar Cells (PVSCs).[1]

Recently, p-type metal oxides, such as NiO, V₂O₅, CuSCN and CuO, have been introduced into perovskite solar cells (PVSCs) device structures as HTLs. It has been shown that Inorganic p-type semiconductor materials as HTLs have the advantages of improved hole selectivity and Voc values, in perovskite solar cells.[2,3] Nickel cobaltite (NiCo₂O₄) is a p-type transparent conductive oxide (TCO) semiconductor, with a relatively wide optical band gap (~2.1 - 2.4 eV), deep-lying valence band (VB of 5.3 eV) that matches well with the VB of CH₃NH₃PbI₃. Furthermore, NiCo₂O₄ has a much better conductivity compared to NiO (two orders of magnitude higher). These attractive features make NiCo₂O₄ an appropriate material for incorporation as HTL in inverted PVSCs.

Various synthetic routes such as hydrothermal, co-precipitation and thermal decomposition of the precursors such as hydroxide nitrates[4,5] have been developed for the synthesis of NiCo₂O₄. However, the production of high purity and monodispersed NiCo₂O₄ nanoparticles with the above mentioned synthetic approaches has not been achieved at low temperature ranges.

We present, NiCo₂O₄ nanoparticles (NPs) with an average size of ~5 nm and narrow particle-size distribution that prepared using a cost-effective, low-temperature combustion method calcinated at (250 - 300 ^oC) for 4 hours. These nanoparticles enable the formation of compact, smooth and high electrically conductive thin film, which were utilized, for the first time, as HTL in solution processed inverted perovskite solar cell (PVSC). The NiCo₂O₄ NPs-based thin film exhibits a high electrical conductivity (4 S/cm) at room temperature, measured using four-point probe method. The proposed NiCo₂O₄ HTLs processed by doctor-blading methods and for the optimized thickness (~15 nm) show appropriate hole carrier selectivity and negligible PVSCs J-V hysterics. The corresponding PVSC exhibits a high FF = 80% and a power conversions efficiency of 15.5%.[1]

References:

[1] Papadas, I. T.; Ioakeimidis, A.; Armatas, G. S.; Choulis, S. A. Low-Temperature Combustion Synthesis of a Spinel NiCo2O4 Hole Transport Layer for Perovskite Photovoltaics. Adv. Sci. 2018, 5, 1-9.

[2] Shrotriya, V.; Li, G.; Yao, Y.; Chu, C.W.; Yang, Y. Transition metal oxides as the buffer layer for polymer photovoltaic cells. Appl. Phys. Lett. 2006, 88, 73508-73512.

[3] Greiner, M. T.; Helander, M. G.; Tang, W. M.; Wang, Z. B.; Qiu, J.; Lu, Z. H. Universal energy-level alignment of molecules on metal oxides. Nat. Mater. 2011, 11, 76–81.

[4] Marco, J. F.; Gancedo, J. R.; Gracia, Μ. Characterization of the Nickel Cobaltite, NiCo2O4, Prepared by Several Methods: An XRD, XANES, EXAFS, and XPS Study. J. Solid State Chem. 2000, 153, 74–81.

[5] Markov, L.; Petrov, K. Nickel-Cobalt Oxide Spinels Prepared by Thermal Decomposition of Nickel(II)-Cobalt(II) Hydroxide Nitrates. Reactivity of Solids 1986, 1, 319–327.

Acknowledgements:

This project received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 647311).

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