Global Frontier Center for Multiscale Energy Systems , Seoul 151-742, Republic of Korea.
Department of Mechanical Engineering, Seoul National University , Seoul 151-742, Republic of Korea.
Nano Lett. 2016 Sep 14;16(9):5756-63. doi: 10.1021/acs.nanolett.6b02473. Epub 2016 Aug 11.
Enhancing hole extraction inside the perovskite layer is the key factor for boosting photovoltaic performance. Realization of halide concentration gradient perovskite materials has been expected to exhibit rapid hole extraction due to the precise bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide perovskite layer is expected to enhance moisture stability without a loss of current density. However, conventional synthetic techniques of perovskite materials such as the solution process have not achieved the realization of halide concentration gradient perovskite materials. In this report, we demonstrate the fabrication of Br concentration gradient mixed halide perovskite materials using a novel and facile halide conversion method based on vaporized hydrobromic acid. Accelerated hole extraction and enhanced lifetime due to Br gradient was verified by observing photoluminescence properties. Through the combination of secondary ion mass spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis, the diffusion behavior of Br ions in perovskite materials was investigated. The Br-gradient was found to be eventually converted into a homogeneous mixed halide layer after undergoing an intermixing process. Br-substituted perovskite solar cells exhibited a power conversion efficiency of 18.94% due to an increase in open circuit voltage from 1.08 to 1.11 V and an advance in fill-factor from 0.71 to 0.74. Long-term stability was also dramatically enhanced after the conversion process, i.e., the power conversion efficiency of the post-treated device has remained over 97% of the initial value under high humid conditions (40-90%) without any encapsulation for 4 weeks.
提高钙钛矿层中的空穴提取效率是提高光伏性能的关键因素。卤化物浓度梯度钙钛矿材料的实现有望由于精确的能带隙调谐而表现出快速的空穴提取。此外，在三碘化钙钛矿层上形成富溴区有望在不降低电流密度的情况下提高水分稳定性。然而，钙钛矿材料的传统合成技术，如溶液法，尚未实现卤化物浓度梯度钙钛矿材料的实现。在本报告中，我们展示了使用基于汽化氢溴酸的新型简便卤化物转化方法制备 Br 浓度梯度混合卤化物钙钛矿材料。通过观察光致发光性质，验证了 Br 梯度引起的空穴提取加速和寿命延长。通过二次离子质谱和电子显微镜与能量色散 X 射线光谱分析的结合，研究了 Br 离子在钙钛矿材料中的扩散行为。发现 Br 梯度在经历混合过程后最终转化为均匀的混合卤化物层。由于开路电压从 1.08V 增加到 1.11V，填充因子从 0.71 提高到 0.74，Br 取代的钙钛矿太阳能电池的功率转换效率提高到 18.94%。转换过程后，长期稳定性也得到了显著提高，即在没有任何封装的情况下，在 4 周内，处理后的器件的功率转换效率在高湿度条件（40-90%）下保持在初始值的 97%以上。
