Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
DOI: https://doi.org/10.29363/nanoge.hopv.2023.031
Publication date: 30th March 2023
Single junction perovskite solar cells have rapidly become the most promising emerging photovoltaic technology, with record efficiencies now on-par with established silicon technology. A logical next step in the development of perovskite photovoltaic technology is the all-perovskite tandem solar cell. By harvesting a broader range of the solar spectrum more efficiently, tandem solar cells can achieve power conversion efficiencies exceeding those of single junction solar cells. Record efficiencies for all-perovskite tandem solar cells have recently overtaken single junction perovskite solar cell records, but are still far from their theoretical maximum. Better understanding of device properties is essential to systematically increase the performance of all-perovskite tandem solar cells. However, the increased complexity of tandem solar cells complicates the study of device properties.
This work explores the use of electrochemical impedance spectroscopy to study recombination and ion migration processes in all-perovskite solar cells. It is shown that interpreting results is challenging due to the overlapping signal of the tandem sub-cells. However, magnitude and frequency of the impedance spectrum change significantly with light intensity. By precisely controlling how much light is absorbed in each sub-cell by adjusting the emission spectrum of an LED solar simulator, we show that it is possible to selectively enhance or suppress impedance signals arising from each individual sub-cell. This enables the investigation of individual sub-cells within the tandem device stack. We show that our method even works for tandems in which the impedance signal of both sub-cells strongly overlaps, allowing us to extract recombination and ionic motion time constants for the individual sub-cells. Studying individual sub-cells will make it easier to find bottlenecks and allows targeted improvement strategies. The methodology developed in this work makes electrochemical impedance spectroscopy a powerful tool to improve the performance of all-perovskite (and other) tandems, and will allow these solar cells to unlock their full potential.
The authors acknowledge the EPSRC (EP/T02030X/1) for funding. Part of this work was undertaken using equipment facilities provided by the Henry Royce Institute, via the grant Henry Royce Institute, Cambridge Equipment: EP/P024947/1 with additional funding from the “Centre for Advanced Materials for Integrated Energy Systems (CAM-IES)” (EP/P007767/1).
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