Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.014
Publication date: 6th July 2018
The development of third generation photovoltaics relies on the use of materials displaying a heterogeneous morphology at the mesoscopic or nanoscopic scale. A universal problem consists in identifying the sources of carrier losses (due to chemical, structural and interfacial defects) by recombination of photo-generated charge carriers. In nano-phase segregated organic bulk heterojunction (BHJs) thin films, a number of questions remain open concerning the impact of the donor-acceptor phases and interfaces morphology on the photo-carrier dynamics. It is also crucial to assess the impact of grain boundaries, chemical impurities and other local defects on the photo-carrier recombination in polycrystalline films of hybrid organic-inorganic perovskites.
In this communication, we will present the state of the art and ongoing developments in local measurements of the photo-carrier dynamics in organic and hybrid solar cell materials by time-resolved Kelvin probe force microscopy. After introducing the basic concepts of time-resolved surface photo-voltage (trSPV) imaging by KPFM under frequency-modulated illumination[1-3] ( FMI-KPFM), we will discuss several key issues and technical hints. What is the achievable lateral and temporal resolution? How shall we take into account photo-induced capacitive changes[4] in the analysis of FMI-KPFM data? We will also introduce a new experimental methodology combining FMI-KPFM with surface potential transients imaging, and we will explain what its benefits are for a proper data analysis and for simultaneous investigations of “fast” and “slow” SPV dynamics.
All items will be discussed in the light of experimental results obtained on BHJs, hybrid perovskites thin films and single crystals. In the last case, we will moreover show that the surface photovoltage and crystal photostriction can be simultaneously investigated by implementing a specific experimental protocol. Last, we will explain how the comparison with model photovoltaic type-II interfaces based on 2D transition metal dichalcogenides heterojunctions[5] shall help us in understanding the more complex case of BHJs.
References
[1] M. Takihara, T. Takahashi, T. Ujihara, Appl. Phys. Lett., 2008, 93, 021902 (3pp).
[2] G. Shao, M. Glaz, M. Fei, H. Ju, D. Ginger, ACS Nano, 2014, 8, 10799-10807.
[3] P. A. Fernández Garrillo, Ł. Borowik, F. Caffy, R. Demadrille, B. Grévin, ACS Appl. Mater. Interfaces, 2016, 8, 31460–31468.
[4] Z. Schumacher, Y. Miyahara, A. Spielhofer, P. Grutter, Phys. Rev. Appl. 2016, 5, 044018 (6pp).
[5] Y. Almadori, D. Moerman, J. Llacer Martinez, Ph. Leclère, B. Grévin, accepted for publication in BJNANO
[6] Y. Almadori, N. Bendiab, B. Grévin, ACS Appl. Mater. Interfaces, 2018, 10, 1363-1373.
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