Interface Design in Wide-Gap Perovskite Solar Cells
Pietro Caprioglio a
a Oxford University, Department of Physics, United Kingdom
Proceedings of Device Physics Characterization and Interpretation in Perovskite and Organic Materials (DEPERO)
València, Spain, 2023 October 3rd - 5th
Organizers: Sandheep Ravishankar, Juan Bisquert and Evelyne Knapp
Invited Speaker, Pietro Caprioglio, presentation 019
Publication date: 14th September 2023

The most promising technological application of perovskite solar cells (PSCs) relies on the implementation of single junction perovskite photovoltaic devices in tandem architectures, either as Si-perovskite or all-perovskite. Notoriously, wide-gap perovskites (⁓1.7-1.8 eV) required for such solar cell design are known to suffer from larger open-circuit voltage (VOC) losses compared to the narrower gap counterparts. Commonly, these types of issues are attributed to an inherent poor material quality, due to either a larger density of traps or to phase instability. However, we demonstrate that these energy losses are associated with strong interface recombination due to an energy misalignment between the perovskite and charge transport layers (CTL), resulting in the external VOC being lower compared to the internal quasi-Fermi level splitting (QFLS) of the same device. While at the p-interface there is a large variety of transport materials that can be used to mitigate this problem (metal oxides, polymers, and self-assembled monolayers), at the n-interface, fullerenes have been the only successful option so far. Due to this limitation, the non-radiative recombination losses at the n-interface are currently one of the major limitations of wide-gap perovskite solar cells. However, we will show, with different examples, how an appropriate interface design can significantly reduce the non-radiative recombination losses at both interfaces. Consequently, the QFLS-VOC mismatch is reduced, allowing for accessing the actual thermodynamic potential of the perovskite absorber, even for wide-gap systems. Moreover, we will show how the interfaces can additionally have a strong impact on the energy losses occurring at short-circuit conditions, due to ion movement. As such, by coupling a theoretical and experimental approach, we demonstrate that most of the energy losses in these systems are not related to the absorber itself and particular attention should be focused on the cell architecture in order to achieve a more successful implementation of these devices in tandem configurations.

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