Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics 2018 (AP-HOPV18)
DOI: https://doi.org/10.29363/nanoge.ap-hopv.2018.022
Publication date: 27th October 2017
The Importance of Interface Morphology for Hysteresis-Free Perovskite Solar Cells
Jay B. Patel1, Jennifer Wong-Leung2, Stephan Van Reenen1, Nobuya Sakai1, Jacob Wang1, Elizabeth S. Parrott1, Mingzhen Liu1, Henry J. Snaith1, Laura M. Herz1,
Michael B. Johnston1
1 University of Oxford, Oxford, OX1 3PU, United Kingdom
2The Australian National University, Canberra, ACT 2601, Australia
michael.johnston@physics.ox.ac.uk
Hybrid metal-halide perovskite materials show great promise for photovoltaic devices, with power conversion efficiencies (PCE) having recently exceeded 22%. However, hybrid metal-halide perovskite photovoltaic devices have been affected by anomalous hysteresis, whereby the current-voltage (J-V) characteristics are dependent upon both scan rate and direction. [1] Furthermore, discrepancies have been reported between the initial measured solar cell efficiency and measurements taken after holding the device at a sustained bias over a period (stabilised power output). To understand the cause of the anomalous hysteresis, we use optimised thermally evaporated perovskite solar cells and then characterise them with high resolution microscopy and current-voltage scans. [2] We demonstrate using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) that under identical growth conditions the interface affects perovskite morphology and crystallinity. We further correlate this with electron diffraction patterns of the perovskite at the interface. We find that the devices that are hysteretic incorporate amorphous regions of perovskite at the interface with the electron transport layer leading to poor charge collection efficiency, charge recombination, and is likely to result in device hysteresis via an electrical capacitive effect across the amorphous region.[3] However, when the perovskite is grown on top of an organic layer, such as PCBM, the interface consists of only crystalline perovskite. Not only does this lead to a hysteresis free device, it also leads to the device exhibiting a stabilised power output which is comparable to the measured solar cell efficiency from the J-V characterisation.
References
[1] H. J. Snaith, A. Abate, J. M. Ball, G. E. Eperon, T. Leijtens, N. K. Noel, S. D. Stranks, J. T.-W. Wang, K. Wojciechowski, W. Zhang, J. Phys. Chem. Lett. 2014, 5, 1511
[2] J. B. Patel, J. Wong-Leung, S. Van Reenen, N. Sakai, J. T. W. Wang, E. S. Parrott, M. Liu, H. J. Snaith, L. M. Herz, M. B. Johnston, Adv. Electron. Mater. 2017, 3, 1600470
[3] L. Cojocaru, S. Uchida, P. V. V. Jayaweera, S. Kaneko, J. Nakazaki, T. Kubo, H. Segawa, Chem. Lett. 2015, 44, 1750.
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