Stability of narrow bandgap lead-tin perovskite material and photovoltaic devices

Stability of narrow bandgap lead-tin perovskite material and photovoltaic devicesFlorine Rombach a, Akash Dasgupta a, Manuel Kober-Czerny a, James Ball a, Joel Smith a, Heon Jin a, Michael Farrer a, Henry Snaith aa Department of Physics, University of Oxford, UKInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Florine Rombach, presentation 045DOI: https://doi.org/10.29363/nanoge.hopv.2024.045Publication date: 6th February 2024Narrow bandgap perovskite solar cells based on mixed lead-tin perovskites tend to suffer from poor stability under operating conditions. This impedes the development of stable all-perovskite multi-junction solar cells. We explore the causes of this instability under extended periods of combined 65°C thermal and illumination stressing using a range of structural, optical, and electronic characterization techniques on lead-tin perovskite films, half-stacks and devices. We show that the bulk phase, absorbance, mobility and background carrier density of lead-tin perovskite films are stable on timescales that exceed those of device degradation. We also find that non-radiative recombination rates in the perovskite increase moderately during the first few hundred hours of stressing. However, through a combination of device simulations and variable rate current-voltage (J-V) scanning we demonstrate that this change can only account for a small portion of the observed device performance loss. Ultimately, we identify a rapidly increasing impact of mobile ions during aging as the major cause of the observed device degradation. A close investigation of the J-V characteristics of devices reveals the formation of a charge extraction barrier during aging, which is hugely reduced in very fast J-V scans where mobile ions are less able to aggregate at interfaces. We quantify the increasing impact of mobile ions on device performance during aging, and furthermore demonstrate that this impact can be significantly mitigated by an alternative hole transport layer choice. Over longer timescales, we additionally identify the growth of a non-perovskite degradation phase as well as HTL-dependent changes in optoelectronic properties. We quantify the impact of these changes on device performance in comparison to the effects from mobile ions, demonstrating that the dominant effect can change with aging time and device architecture. Thus, we are able to closely identify the various processes that limit the stability of lead-tin perovskite solar cells and make recommendations to overcome these challenges. © FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. 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