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Energetische Anpassung innerer Kontakte und maßgeschneiderter Grenzflächen in Photoelektrochemischen Multi-Absorber Solarzellen

Fachliche Zuordnung Herstellung und Eigenschaften von Funktionsmaterialien
Förderung Förderung von 2019 bis 2023
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 424924805
 
Erstellungsjahr 2024

Zusammenfassung der Projektergebnisse

In summary, the experiments have shown that dangling bond pinning defects in Si reduce the performance of all heterointerfaces where the absorber layer Si is in direct contact to a heterointerface including electrolyte layers. More promising are buried junction with Si p-n homojunctions. However, the formation of catalyst and passivation layers cannot yet be realized in an optimal manner. At this point, it has to be conceded that the differences in electrochemical performance cannot yet be fully elucidated by the interface model experiment, only considering interface energetics from a thin film approach. Accordingly, it is suggested that mechanical and electrochemical stability, as well as lateral homogeneities have to be considered as well to fully understand the differences in performances and improve the performance level of the pn+ - Si/Pt photocathode for the different needed deposition techniques. We showed that two atomically-well-ordered surfaces of AlInP(001) can be prepared in a MOCVD reactor with either phosphorus- or group III-termination. The surface termination has a significant impact on the water and oxygen interaction with the surface. While the AlInP surfaces passivated by P-P dimers do not attract water and oxygen, despite the fact that Al-containing layers are known as O-attractive surfaces, on the group III-rich surface, the In-In bonds in the second monoloayer serve as active sites for reacting with water molecules. At the AlInP/GaInP(001) heterointerfaces, a critical interface in photoelectrochemical devices for water splitting, we found pinning of the Fermi level by localized electronic states. The next step was the passivation of the absorbers with TiO2-based passivation layers. For Si, this consistently resulted in the formation of Ti3+-related defect states in the bandgap that pin the Fermi level. P-rich p-type InP could be passivated with ALD-grown TiO2 layers without the formation of Ti3+ defect states. Films with a thickness of 2.5 nm or more were found to completely cover the InP surface. A series of InP/TiO2 films with thicknesses between 1 – 10 nm were transferred to PA3 for in-depth electron dynamics studies. The experimental activities described have been complemented by theoretical work based on density functional theory. These concern surface reconstruction and surface states of pure surfaces and surfaces in the presence of hydrogen, oxygen, and water. Perhaps the most surprising result was that even the relatively few P-dangling bonds of the P-rich InP surface, which for entropic reasons is not saturated with hydrogen at finite temperatures, can lead to Fermi energy pinning and considerable band bending. In addition to binary compounds, first semiconductor alloys have been investigated and the water interface has been modeled using molecular dynamics. The project activities have initiated several related activities in the theory group at TUIL. These include the modeling of RAS spectra, the evaluation of phonon frequencies, and the description of the formation and dynamics of bulk defects. The latter is currently being transferred to surface defects in the presence of aqueous solutions.

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