Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
ACS Appl Mater Interfaces. 2023 Jun 14;15(23):28008-28022. doi: 10.1021/acsami.3c03359. Epub 2023 May 30.
Since the emergence of organometal halide perovskite (OMP) solar cells, there has been growing interest in the benefits of incorporating polymer additives into the perovskite precursor, in terms of both photovoltaic device performance and perovskite stability. In addition, there is interest in the self-healing properties of polymer-incorporated OMPs, but the mechanisms behind these enhanced characteristics are still not fully understood. Here, we study the role of poly(2-hydroxyethyl methacrylate) (pHEMA) in improving the stability of methylammonium lead iodide (MAPI, CHNHPbI) and determine a mechanism for the self-healing of the perovskite-polymer composite following exposure to atmospheres of differing relative humidity, using photoelectron spectroscopy. Varying concentrations of pHEMA (0-10 wt %) are incorporated into a PbI precursor solution during the conventional two-step fabrication method for producing MAPI. It is shown that the introduction of pHEMA results in high-quality MAPI films with increased grain size and reduced PbI concentration compared with pure MAPI films. Devices based on pHEMA-MAPI composites exhibit an improved photoelectric conversion efficiency of 17.8%, compared with 16.5% for a pure MAPI device. pHEMA-incorporated devices are found to retain 95.4% of the best efficiency after ageing for 1500 h in 35% RH, compared with 68.5% achieved from the pure MAPI device. The thermal and moisture tolerance of the resulting films is investigated using X-ray diffraction, in situ X-ray photoelectron spectroscopy (XPS), and hard XPS (HAXPES). It is found that exposing the pHEMA films to cycles of 70 and 20% relative humidity leads to a reversible degradation, via a self-healing process. Angle-resolved HAXPES depth-profiling using a non-destructive Ga Kα source shows that pHEMA is predominantly present at the surface with an effective thickness of ca. 3 nm. It is shown using XPS that this effective thickness reduces with increasing temperature. It is found that N is trapped in this surface layer of pHEMA, suggesting that N-containing moieties, produced during reaction with water at high humidity, are trapped in the pHEMA film and can be reincorporated into the perovskite when the humidity is reduced. XPS results also show that the inclusion of pHEMA enhances the thermal stability of MAPI under both UHV and 9 mbar water vapor pressure.
自从有机金属卤化物钙钛矿 (OMP) 太阳能电池出现以来，人们越来越关注在钙钛矿前驱体中加入聚合物添加剂的好处，这对光伏器件的性能和钙钛矿稳定性都有好处。此外，人们还对聚合物掺入 OMP 的自修复特性感兴趣，但这些增强特性的背后机制仍未完全了解。在这里，我们研究了聚(2-羟乙基甲基丙烯酸酯) (pHEMA) 在提高碘化甲基铵 (MAPI，CHNHPbI) 稳定性方面的作用，并通过光电子能谱确定了在不同相对湿度的大气中暴露后钙钛矿-聚合物复合材料自修复的机制。在传统的两步法制备 MAPI 的过程中，将不同浓度的 pHEMA(0-10wt%) 掺入 PbI 前驱体溶液中。结果表明，与纯 MAPI 薄膜相比，引入 pHEMA 可得到具有更大晶粒尺寸和更低 PbI 浓度的高质量 MAPI 薄膜。基于 pHEMA-MAPI 复合材料的器件的光电转换效率提高到 17.8%，而纯 MAPI 器件为 16.5%。在 35%RH 下老化 1500 小时后，pHEMA 掺入的器件保留了 95.4%的最佳效率，而纯 MAPI 器件仅为 68.5%。通过 X 射线衍射、原位 X 射线光电子能谱 (XPS) 和硬 XPS (HAXPES) 研究了所得薄膜的热和耐湿性。结果发现，通过自修复过程，暴露于 70%和 20%相对湿度循环的 pHEMA 薄膜会发生可逆降解。使用非破坏性 Ga Kα 源的角度分辨 HAXPES 深度剖析表明，pHEMA 主要存在于表面，有效厚度约为 3nm。XPS 表明，随着温度的升高，有效厚度会降低。结果表明，N 被捕获在 pHEMA 的这个表面层中，这表明在高湿度下与水反应时生成的含 N 部分被捕获在 pHEMA 薄膜中，当湿度降低时可以重新掺入钙钛矿中。XPS 结果还表明，在 UHV 和 9 毫巴水蒸气压力下，pHEMA 的存在均增强了 MAPI 的热稳定性。
