Department of Electrical and Computer Engineering, The University of Toronto , Toronto, ON M5S 3G4, Canada.
Nano Lett. 2014 Nov 12;14(11):6281-6. doi: 10.1021/nl502612m. Epub 2014 Oct 13.
Photovoltaic devices based on lead iodide perovskite films have seen rapid advancements, recently achieving an impressive 17.9% certified solar power conversion efficiency. Reports have consistently emphasized that the specific choice of growth conditions and chemical precursors is central to achieving superior performance from these materials; yet the roles and mechanisms underlying the selection of materials processing route is poorly understood. Here we show that films grown under iodine-rich conditions are prone to a high density of deep electronic traps (recombination centers), while the use of a chloride precursor avoids the formation of key defects (Pb atom substituted by I) responsible for short diffusion lengths and poor photovoltaic performance. Furthermore, the lowest-energy surfaces of perovskite crystals are found to be entirely trap-free, preserving both electron and hole delocalization to a remarkable degree, helping to account for explaining the success of polycrystalline perovskite films. We construct perovskite films from I-poor conditions using a lead acetate precursor, and our measurement of a long (600 ± 40 nm) diffusion length confirms this new picture of the importance of growth conditions.
基于碘化铅钙钛矿薄膜的光伏器件取得了飞速发展，最近其经认证的太阳能转化效率达到了惊人的 17.9%。研究报告一致强调，生长条件和化学前体的具体选择对于实现这些材料的优异性能至关重要；然而，对于材料加工路线选择的作用和机制仍了解甚少。在这里，我们表明，在富含碘的条件下生长的薄膜容易产生高密度的深电子陷阱（复合中心），而使用氯化物前体可以避免形成关键缺陷（被碘取代的铅原子），这些缺陷会导致扩散长度短和光伏性能差。此外，还发现钙钛矿晶体的最低能量表面完全没有陷阱，保持了电子和空穴的离域程度，这在一定程度上有助于解释多晶钙钛矿薄膜的成功。我们使用醋酸铅前体制备了贫碘条件下的钙钛矿薄膜，我们对长（600 ± 40nm）扩散长度的测量证实了这一生长条件重要性的新观点。
