Sol-gel processed niobium oxide thin film suitable for a scaffold layer of perovskite solar cells


Increasing stringent mitigation measures on the use of fossil fuels have favored the development of renewable energy as an alternative energy source. This has resulted in a keen interest in solar energy. In particular, organic-inorganic halide perovskite solar cells have increasingly gained popularity as a low-cost energy device since their interception more than a decade ago. For instance, a relatively high increase in power conversion efficiency has recently improved to 25.2% up from 3.81%. This can be attributed to their excellent optoelectronic properties and high mobility charge carriers. However, there is still a great need to develop more efficient strategies for improving the performance of the devices and utilizing the full potential of perovskite materials through fabricating highly homogenous and crystalline planar perovskite thin-films.

Presently, several processes for synthesizing perovskite materials have been developed. These processes majorly involve the use of different solvents, addition of additives and varying the compositions. Despite the good progress, optimizing the crystallization and formation of thin-film kinetics of the perovskite materials has remain a big challenge. Recently, substrate surface modification has been identified as a promising approach for effective control of the perovskite films. Specifically, the scaffold layer of the perovskite film is of great significance in enhancing crystallization and morphological evolutions as well as ensuring selective extraction of the photo-excited electrons. Among the available metal oxides, niobium oxide-based scaffold layer has exhibited higher blocking effects as compared to other metal oxides such as titanium oxide. This has further led to its application in perovskite solar cells. Despite the effectiveness of the currently available methods for niobium oxide films fabrication such as magnetron sputtering, the development of more cost-effective methods is still highly desirable.

To this end, Hosei University researchers: Dr. Eiichi Inami (Associate Professor at Kochi University of Technology at present), Professor Takamasa Ishigaki, and Professor Hironori Ogata investigated the optoelectronic and morphological properties as well as the performance of a niobium oxide scaffold layer synthesized using the sol-gel methods. The main objective was to decrease further the processing cost, much lower than that of the magnetron sputtering technique. Fundamentally, they fabricated three different types of film: niobium oxide, m-titanium oxide, and compact titanium oxide film. Eventually, they compared their morphological and optoelectronic properties using various characterization techniques such as scanning electron microscopy and X-ray diffraction. The work is currently published in the research journal, Thin Solid Films.

The authors observed that the niobium oxide scaffold layer facilitated efficient crystallization of the perovskite film as compared to other conventional mesoporous titanium oxide scaffold layers thus may lead to the high performance of the perovskite solar cell. This was attributed to the high crystallization of the perovskite film and efficient electron transport layer. Generally, the sol-gel processed niobium oxide scaffold layers are a promising solution for design and fabrication of high performance and cost-effective perovskite solar cells. Furthermore, the study by Kochi University of Technology and Hosei University scientists provides essential information that will pave way for the synthesis of the various structure resulting from the niobium oxide i.e. nanotube, nanosheet, and nanochannel, which may, in turn, be used as scaffold layers to enhance the device performance.

Sol-gel processed niobium oxide thin film suitable for a scaffold layer of perovskite solar cells - Advances in Engineering

About the author

Dr. Eiichi Inami is currently an Associate Professor of School of Systems Engineering at Kochi University of Technology, Japan, and a Guest Associate Professor of Graduate School of Engineering Science at Osaka University, Japan. He received his Ph.D. (Engineering) in 2009 from Osaka University where he also worked as an Assistant Professor, a Specially Appointed Assistant Professor, and a Specially Appointed Lecturer from 2005 to 2015. Then he moved to Hosei University, Japan, as a Postdoctoral Researcher for one year. Afterward, he worked as a Specially Appointed Lecturer at Chiba University, Japan, from 2016 to 2018.

His main research fields are surface science and nano-materials science and technology. Much of the current research in his group focuses on controlled surface modifications with atomic-scale, on-surface single-molecule-level chemistry, atomic-scale fabrication and characterization of novel functional materials, and their applications to high-performance electronic/optoelectronic devices.

E mail: [email protected]

About the author

Dr. Takamasa Ishigaki is Professor with Department of Chemical Science and Technology, and Director of Micro-Nano Technology Research Center, both at Hosei University. His main areas of expertise include ceramic science, plasma chemistry and solid-state chemistry.

His group focuses on the synthesis of nano- and micron- size ceramic powders for environmental and optical applications. Dr. Ishigaki’s research has generated 3 edited books, 273 refereed papers/book chapters, and resulted in more than 400 presentations at national/international meetings, including 71 invited lectures.

About the author

Dr. Hironori Ogata is currently a Professor of the Department of Chemical Science and Technology, Faculty of Bioscience and Applied Chemistry at Hosei University, Japan where he has been since 2008. He also currently serves as Professor of Graduate School of Science and Engineering(Major in Applied Chemistry) at Hosei University. He received his Ph.D. in Functional Material Science from the Graduate University for Advanced Studies in 1993. He worked at Institute for Molecular Science in Okazaki as a Research Associate from 1993 to 2001.

His research interests span both the development of novel highly functional nanomaterials materials with low environmental impact and their related device applications including photovoltaic cells.


Inami, E., Ishigaki, T., & Ogata, H. (2019). Sol-gel processed niobium oxide thin-film for a scaffold layer in perovskite solar cells. Thin Solid Films, 674, 7-11.

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