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| Book/Dissertation / PhD Thesis | FZJ-2026-02330 |
2026
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-921-3
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Please use a persistent id in citations: doi:10.34734/FZJ-2026-02330
Abstract: Due to the rapid depletion of finite conventional fossil fuels and the resultant greenhouse effect, high-efficiency solar cells that convert renewable and clean solar energy into electricity have rapidly gained prominence in the energy market and become a dominant force in the field of renewable energy. The objective of this thesis is to develop highefficiency perovskite/silicon tandem solar cells, as the tandem configuration surpasses the theoretical efficiency limit of single-junction solar cells and demonstrates significant potential for generating increased electricity at comparable costs. In particular, entire fabrication chain of tandem solar cells, tin oxide (SnOX) as the buffer layer and transparent conductive oxides (TCOs) as transparent electrode in the perovskite top cells, and various techniques for the efficiency improvement from 9% to 33% have been investigated. The main focus of the SnOX and TCOs lies on the fundamental understanding of the material properties, whereas for the perovskite/silicon tandem solar cell topic, developments on device level and investigation of working mechanism are the key aspects. The configuration of perovskite/silicon tandem solar cells differs from that of both single-junction perovskite and silicon solar cells. Consequently, the entire fabrication process for tandem devices is not a simple combination of the fabrication processes of two single-junction devices. Rather, it requires the targeted design and adjustment of deposition masks for different substrates and for each film, taking into account the substrate thickness, film area, and the characteristics of the various deposition techniques employed for film preparation. Following the successful establishment of the complete fabrication process, the initial batch of perovskite/silicon tandem solar cells was produced for workflow testing, yielding a maximum initial efficiency of 9%. The implementation of TCOs in perovskite top cells as transparent electrodes, typically prepared by magnetron sputtering, necessitates a robust buffer layer to mitigate the inevitable sputter-induced damage to the underlying organic films, in order to achieve high efficiency. Following the successful development of atomic layer depositions of homogeneous SnOX single layer, the transitional structure (single-junction) was fabricated with high efficiency exceeding 20% through a systematic optimization of the deposition parameters. Although SnOX has been widely utilized as a sputter buffer layer in perovskite/silicon tandem solar cells, independent research on its working mechanisms has rarely been conducted. Consequently, the working mechanism of SnOX at the C60/Ag interface was investigated as an ideal reference for understanding the working mechanism of SnOX in perovskite top cells. This study examines the correlation between the SnOX process and the photovoltaic parameters using a series of experiments, characterizations, and simulations. It is observed that the efficiency increased with thicker SnOX, and the results suggest that thicker SnOX has the potential to suppress non-radiative recombination, decrease the series resistance of perovskite solar cells, and ensure an overall improved selectivity of the contact for charge carrier collection. Owing to the complex configuration of tandem solar cells, semi-transparent perovskite solar cells are typically fabricated and investigated as a reference to address the corresponding issues associated with the insertion of window stack, comprising a buffer layer and a transparent electrode, in perovskite top cells. After the successful establishment of the fabrication chain of semi-transparent devices, TCOs as the transparent electrode were developed using magnetron sputtering and the optoelectrical properties were tuned to minimize parasitic absorption and electrical losses. The origin of S-shape in the current density-voltage (JV) characteristics was revealed to be the presence of an extraction barrier at the SnOX/TCO interface and was completely eliminated by increasing the thickness of SnOX buffer layer in the semi-transparent devices, which is generally known as the mitigation of sputter damage. The conventional understanding of the origin of sputtering damage is attributed to high-kinetic-energy ion bombardment and/or plasma radiation generated during sputtering. In fact, through decoupling these two factors, our investigation of their individual effects on bare films, layer stacks, and complete devices revealed that the sputtering damage of ITO to perovskite/C60 stacks primarily originates from ion bombardment rather than plasma radiation due to the generation of vacancy defects within the C60 and the dissociation of C=N bonds at the perovskite surface. In contrast, plasma radiation exhibits great potential for suppressing nonradiative recombination within perovskite films. After the optimization of the fabrication chain, perovskite-related layer stack, and window stack, the maximum efficiency of perovskite/silicon tandem solar cells increased to 19%. Subsequently, a series of methodologies, primarily focused on optical and electrical aspects, were implemented to further enhance the efficiency to 31%. Ultimately, surface treatment on the silicon bottom cells was found to exert a significant influence on surface morphology, potential distribution, energy levels, coverage, wettability, crystallization, and optical response of certain critical films in subcells, consequently affecting device performance. After the optimization of the O2 plasma treatment and wet-chemical cleaning, a peak efficiency of 33% was achieved for perovskite/silicon tandem solar cells.
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