Mobile Iodine Capture Technology Enhances the Stability of Perovskite Solar Cells

Background Introduction

Perovskite Solar Cells (PSCs) are considered promising candidates for future photovoltaic power generation due to their high efficiency and low cost. However, the stability issues of perovskite materials themselves, particularly photolysis and ion migration, severely affect their practical application. Specifically, defects such as iodide (Iodide) and iodine vacancies (Iodine Vacancies) can trigger self-accelerating chemical reactions under light and bias conditions, leading to rapid degradation of the perovskite material. Therefore, finding ways to capture and stabilize iodine-related defects is of significant importance to improve the stability of PSCs.

Paper Source

This paper is authored by Xiaoxue Ren, Jifei Wang, Yun Lin, Yingwei Wang, Haipeng Xie, Han Huang, Bin Yang, Yanfa Yan, Yongli Gao, Jun He, Jinsong Huang, and Yongbo Yuan, affiliated with institutions such as the College of Materials Science and Engineering at Hunan University, the School of Physics and Electronics at Central South University, and the Department of Physics and Astronomy at the University of Toledo. The paper was published in the journal Nature Materials, and the article DOI is https://doi.org/10.1038/s41563-024-01876-2.

Research Process

The research aims to propose a new strategy to protect perovskite solar cells by capturing dynamically released iodine and preventing iodide (ix-) loss through interface materials. The paper details the following experimental steps:

1. Introduction of Exogenous Iodine Molecules: Researchers introduced exogenous iodine (I2) molecules onto the perovskite surface by spin-coating an iodine/isopropanol solution to simulate accelerated degradation conditions. It was found that the introduced iodine molecules accelerate the degradation of perovskites under light exposure.

2. Protection by Soft Lewis Acids: By covering the perovskite surface with a small amount of soft Lewis acids such as C60, PCBM, PFi, and 5FiB, it was found that these materials can effectively capture iodine molecules and significantly reduce the degradation rate of the perovskite materials. Specific experiments showed that a C60-covered perovskite film improves stability by about ten times under UV light irradiation.

3. Validation by Raman Spectroscopy Mapping: Using Raman spectroscopy mapping in different regions, it was found that the C60 layer, whether located on the top or the bottom of the analysis layer, can effectively capture iodide ions (I3-), indicating that the iodine-capturing ability of soft Lewis acids is systemic.

4. Comparison of Different Capturing Agents: A comparison of various organic electron transport materials such as PCBM, C60 with Fai, CSi, or PBi2 showed that PFi has the strongest iodine-capturing ability. This is because the iodine atoms at the carbon-fluorine chain end of PFi have a strong electron-absorbing nature, thereby effectively binding negatively charged I- or IX-.

5. Application of Dynamic Iodine Capture Stability: For addressing the instability of cells under reverse bias, cells using PFi/PCBM/C60 as electron transport layers were able to maintain good stability under extreme reverse bias conditions, while unoptimized cells rapidly decreased in efficiency within a short time.

Main Results

1. Protection Mechanism: The study confirmed that PFi and C60 effectively inhibit ion migration by capturing iodine or iodine radicals released from the perovskite film, preventing interface metal corrosion and improving reverse bias stability.

2. Significant Stability Improvement: The reverse-type perovskite solar cells covered with PFi/PCBM/C60 maintained 90% of their initial efficiency under reverse bias for 100 hours, improving stability by three orders of magnitude. Furthermore, cells with this structure showed significant improvement in stability under UV light and thermal light conditions, increasing by about ten times and thirty times respectively.

3. Prevention of Iodine Loss and Improvement in Manufacturing Yield: During the manufacturing process, the effective prevention of iodide ion loss by the PFi layer resulted in a reduced initial iodine vacancy concentration in the final product, significantly improving the manufacturing yield.

4. Enhancement of Photoelectric Conversion Efficiency: Due to the favorable dipole orientation of PFi molecules for charge collection, the open-circuit voltage (Voc) and photoelectric conversion efficiency (PCE) of perovskite solar cells using PFi/PCBM/C60 as the electron transport layer were also improved.

Conclusion and Value

This study proposes a new method for significantly improving the light, thermal, and electrical stability of perovskite solar cells through an interface iodine/iodide capture strategy. Using PFi/PCBM/C60 as the electron transport layer not only enhances the stability of the cells but also improves the photoelectric conversion efficiency, providing a reliable guarantee for practical applications. This innovation holds significant importance for advancing the commercialization of perovskite solar cells.

By enhancing ion capture capability through targeted halogen bonding, avoiding rapid performance decline under reverse bias, the research points a new direction for efficient and stable perovskite photovoltaic industry, demonstrating enormous application value and potential.