Recently, an international team comprising the Helmholtz Berlin Center for Materials and Energy Research, the Shanghai Institute of Advanced Research, the Shanghai Institute of Advanced Studies at the Chinese Academy of Sciences, and the School of Materials at Henan University made significant strides in the field of perovskite photovoltaics. Their findings were published in Science under the title "Highly efficient pin perovskite solar cells that end temperature variations." This research leveraged the in-situ characterization capabilities of the Shanghai Synchrotron Radiation Facility’s BL14B beamline. This advanced technology provided crucial data that supported the study's groundbreaking discoveries.
Organic-inorganic hybrid halide perovskite-based solar cells have garnered significant attention due to their affordability, ease of fabrication for large-scale applications, and impressive photoelectric conversion efficiencies. However, one major hurdle has been their sensitivity to temperature fluctuations, which can lead to phase transformations and lattice strains in the halide perovskite materials. These changes often result in rapid performance degradation and eventual device failure, hindering widespread adoption. To address this issue, this innovative work highlights how β-poly(1,1-difluoroethylene) enhances the crystallization properties of perovskite films. It effectively passivates surface defects, optimizes energy level alignment, and facilitates carrier transport in pin-structured devices. Importantly, the ordered arrangement of β-poly(1,1-difluoroethylene) at grain boundaries helps buffer grain boundary deformation during temperature changes, releasing lattice stress and preserving the crystal structure's recoverability. This significantly boosts the device's resilience to temperature variations.
To better understand the crystallization process of perovskite films, researchers conducted comprehensive studies using synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS). Comparing GIWAXS results (Fig. 1A, B), it became evident that the initial mesophase of DMSO-DMF-PbX2 was suppressed within the first 60 seconds, attributed to the isolation provided by long-chain β-pV2F molecules. Observations during film formation revealed distinct scattering characteristics centered around q = ~10 nmâ»Â¹ on the (001) crystal plane, signifying solidification and transition to the black phase. The target film exhibited a faster transition to the perovskite black phase compared to the control film, suggesting that β-pV2F accelerates this process by lowering formation energy. By the final stage of crystallization (t7), the target film demonstrated a stronger diffraction signal, indicating superior orderliness.
Further analysis using synchrotron GIWAXS explored how β-pV2F impacts perovskite film morphology and crystal structure under varying temperatures. As illustrated in Figures 2A and B, the target perovskite film showed reduced susceptibility to temperature-induced degradation, with grain boundary deformation during thermal cycling effectively minimized. Figure 2C illustrates perovskite strain changes across temperature cycles, showing that lattice parameters fluctuate. Conversely, the target perovskite maintained stable strain cycles within a narrower range (-0.06% to 0.38%), reflecting its recoverable crystal structure and ability to release lattice stress.
This research not only advances the understanding of perovskite solar cell stability but also paves the way for more robust, temperature-tolerant photovoltaic technologies.
[Figure 1. Crystal kinetics of perovskite films]
[Figure 2. Perovskite structure evolution during temperature cycle]
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