Yin Jun, Cortecchia Daniele, Krishna Anurag, Chen Shi, Mathews Nripan, Grimsdale Andrew C, Soci Cesare
†Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371.
‡Interdisciplinary Graduate School, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
J Phys Chem Lett. 2015 Apr 16;6(8):1396-402. doi: 10.1021/acs.jpclett.5b00431. Epub 2015 Apr 1.
Solar cells based on organic-inorganic lead iodide perovskite (CH3NH3PbI3) exhibit remarkably high power conversion efficiency (PCE). One of the key issues in solution-processed films is that often the polycrystalline domain orientation is not well-defined, which makes it difficult to predict energy alignment and charge transfer efficiency. Here we combine ab initio calculations and photoelectron spectroscopy to unravel the electronic structure and charge redistribution at the interface between different surfaces of CH3NH3PbI3 and typical organic hole acceptor Spiro-OMeTAD and electron acceptor PCBM. We find that both hole and electron interfacial transfer depend strongly on the CH3NH3PbI3 surface orientation: while the (001) and (110) surfaces tend to favor hole injection to Spiro-OMeTAD, the (100) surface facilitates electron transfer to PCBM due to surface delocalized charges and hole/electron accumulation at the CH3NH3PbI3/organic interfaces. Molecular dynamic simulations indicate that this is due to strong orbital interactions under thermal fluctuations at room temperature, suggesting the possibility to further improve charge separation and extraction in perovskite-based solar cells by controlling perovskite film crystallization and surface orientation.
基于有机-无机碘化铅钙钛矿（CH3NH3PbI3）的太阳能电池展现出极高的功率转换效率（PCE）。溶液处理薄膜中的一个关键问题是，多晶畴取向通常不明确，这使得预测能量排列和电荷转移效率变得困难。在此，我们结合从头算计算和光电子能谱，以揭示CH3NH3PbI3不同表面与典型有机空穴受体Spiro-OMeTAD和电子受体PCBM之间界面处的电子结构和电荷重新分布。我们发现，空穴和电子的界面转移都强烈依赖于CH3NH3PbI3的表面取向：虽然（001）和（110）表面倾向于有利于空穴注入Spiro-OMeTAD，但（100）表面由于表面离域电荷以及CH3NH3PbI3/有机界面处的空穴/电子积累，促进了电子向PCBM的转移。分子动力学模拟表明，这是由于室温下热涨落作用下的强轨道相互作用，这表明通过控制钙钛矿薄膜结晶和表面取向，有可能进一步提高基于钙钛矿的太阳能电池中的电荷分离和提取效率。
