Sainato Michela, Shevitski Brian, Sahu Ayaskanta, Forster Jason D, Aloni Shaul, Barillaro Giuseppe, Urban Jeffrey J
Dipartimento di Ingegneria dell'Informazione, Università di Pisa, Via G. Caruso 16, 56111 Pisa, Italy.
Molecular Foundry, Lawrence Berkeley National Laboratory, 67 Cyclotron Road, 94720 Berkeley, United States.
ACS Omega. 2017 Jul 18;2(7):3681-3690. doi: 10.1021/acsomega.7b00433. eCollection 2017 Jul 31.
Self-assembly of semiconductor nanocrystals (NCs) into two-dimensional patterns or three-dimensional (2-3D) superstructures has emerged as a promising low-cost route to generate thin-film transistors and solar cells with superior charge transport because of enhanced electronic coupling between the NCs. Here, we show that lead sulfide (PbS) NCs solids featuring either short-range (disordered glassy solids, GSs) or long-range (superlattices, SLs) packing order are obtained solely by controlling deposition conditions of colloidal solution of NCs. In this study, we demonstrate the use of the evaporation-driven self-assembly method results in PbS NC SL structures that are observed over an area of 1 mm × 100 μm, with long-range translational order of up to 100 nm. A number of ordered domains appear to have nucleated simultaneously and grown together over the whole area, imparting a polycrystalline texture to the 3D SL films. By contrast, a conventional, optimized spin-coating deposition method results in PbS NC glassy films with no translational symmetry and much shorter-range packing order in agreement with state-of-the-art reports. Further, we investigate the electronic properties of both SL and GS films, using a field-effect transistor configuration as a test platform. The long-range ordering of the PbS NCs into SLs leads to semiconducting NC-based solids, the mobility (μ) of which is 3 orders of magnitude higher than that of the disordered GSs. Moreover, although spin-cast GSs of PbS NCs have weak ambipolar behavior with limited gate tunability, SLs of PbS NCs show a clear p-type behavior with significantly higher conductivities.
半导体纳米晶体（NCs）自组装成二维图案或三维（2-3D）超结构，已成为一种很有前景的低成本途径，可用于制造具有卓越电荷传输性能的薄膜晶体管和太阳能电池，这是因为NCs之间的电子耦合增强了。在此，我们表明，仅通过控制NCs胶体溶液的沉积条件，就能获得具有短程（无序玻璃态固体，GSs）或长程（超晶格，SLs）堆积顺序的硫化铅（PbS）NCs固体。在本研究中，我们证明了使用蒸发驱动自组装方法可得到PbS NC SL结构，该结构在1 mm×100 μm的区域内被观察到，具有高达100 nm的长程平移有序性。许多有序畴似乎同时成核并在整个区域共同生长，赋予3D SL薄膜多晶织构。相比之下，传统的、经过优化的旋涂沉积方法会导致PbS NC玻璃态薄膜，其没有平移对称性且堆积顺序的范围要短得多，这与现有技术报告一致。此外，我们使用场效应晶体管配置作为测试平台，研究了SL和GS薄膜的电子特性。PbS NCs排列成长程有序的SLs会形成基于半导体NCs的固体，其迁移率（μ）比无序的GSs高3个数量级。此外，尽管PbS NCs的旋铸GSs具有较弱的双极性行为且栅极可调性有限，但PbS NCs的SLs表现出明显的p型行为，且电导率显著更高。
