Photonics and Optoelectronics Group, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.
Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
J Am Chem Soc. 2017 Nov 22;139(46):16462-16465. doi: 10.1021/jacs.7b09319. Epub 2017 Nov 13.
The crucial separation of photocarriers in solar cells can be efficiently driven by contacting semiconductor phases with differing doping levels. Here we show that intrinsic doping surges in methylammonium lead iodide (MAPbI) crystals as a response to environmental basicity. MAPbI crystals were passivated with polybases to induce the deprotonation of its methylammonium ions (MA). Stable crystals showed marked increases in photoluminescence and radiative decay, attributed to the presence of unbalanced charges acting as doped carriers. This emulates in a controlled manner the proton-withdrawing conditions of polycrystalline films, where excess basic precursors are found between grains. Raman spectroscopy showed the collective alignment of MA cations within the intrinsically doped lattices, thus revealing the buildup of electric fields. On this basis, we propose a mechanism for the formation of doping-gradients toward grain boundaries, potentially explaining the extended photocarrier lifetimes and diffusion lengths observed in perovskite solar cells.
在太阳能电池中，光生载流子的有效分离可以通过接触具有不同掺杂水平的半导体相来实现。在这里，我们表明，卤化铅甲胺（MAPbI）晶体中的本征掺杂会随着环境碱度的增加而激增。通过使用多碱基对 MAPbI 晶体进行钝化，来诱导其甲胺离子（MA）的去质子化。稳定的晶体表现出明显增强的光致发光和辐射衰减，这归因于存在不平衡电荷，它们充当掺杂载流子。这以受控的方式模拟了多晶薄膜的质子抽取条件，其中在晶粒之间发现了过量的碱性前体。拉曼光谱显示 MA 阳离子在本征掺杂晶格中的集体排列，从而揭示了电场的建立。在此基础上，我们提出了一种向晶粒边界形成掺杂梯度的机制，这可能解释了在钙钛矿太阳能电池中观察到的扩展光生载流子寿命和扩散长度。
