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The application of molybdenum oxide in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells in the role of hole selective contact. For modeling-based optimization of such contact, knowledge of the molybdenum oxide defect density of states (DOS) is crucial. In this paper, we report a method to extract the defect density through nondestructive optical measures, including the contribution given by small polaron optical transitions. The presence of defects related to oxygen-vacancy and of polaron is supported by the results of our opto-electrical characterizations along with the evaluation of previous observations. As part of the study, molybdenum oxide samples have been evaluated after post-deposition thermal treatments. Quantitative results are in agreement with the result of density functional theory showing the presence of a defect band fixed at 1.1 eV below the conduction band edge of the oxide. Moreover, the distribution of defects is affected by post-deposition treatment.

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Publication history

Received: 17 June 2020
Revised: 02 August 2020
Accepted: 03 August 2020
Published: 02 September 2020
Issue date: December 2020

Copyright

© The Author(s) 2020

Acknowledgements

We thank G. Yang, R. Santbergen and G. Limodio for the fruitful discussions. The authors also thank L. Spitaleri for the assistance with the XPS patterns and Y. Zhou for the assistance with the deposition equipment.

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Email: nanores@tup.tsinghua.edu.cn

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