Pinto Rui M, Gouveia Wilson, Maçôas Ermelinda M S, Santos Isabel C, Raja Sebastian, Baleizão Carlos, Alves Helena
INESC-MN and IN , Rua Alves Redol 9, 1000-029 Lisboa, Portugal.
CQFM and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
ACS Appl Mater Interfaces. 2015 Dec 23;7(50):27720-9. doi: 10.1021/acsami.5b08523. Epub 2015 Dec 10.
The efficiency of organic photodetectors and optoelectronic devices is strongly limited by exciton diffusion, in particular for acceptor materials. Although mechanisms for exciton diffusion are well established, their correlation to molecular organization in real systems has received far less attention. In this report, organic single-crystals interfaces were probed with wavelength-dependent photocurrent spectroscopy and their crystal structure resolved using X-ray diffraction. All systems present a dynamic photoresponse, faster than 500 ms, up to 650 nm. A relationship between molecular organization and favorable exciton diffusion in substituted butyl-perylenediimides (PDIB) is established. This is demonstrated by a set of PDIBs with different intra- and interstack distances and short contacts and their impact on photoresponse. Given the short packing distances between PDIs cores along the same stacking direction (3.4-3.7 Å), and across parallel stacks (2.5 Å), singlet exciton in these PDIBs can follow both Förster and Dexter exciton diffusion, with the Dexter-type mechanism assuming special relevance for interstack exciton diffusion. Yet, the response is maximized in substituted PDIBs, where a 2D percolation network is formed through strong interstack contacts, allowing for PDIBs primary excitons to reach with great efficiency the splitting interface with crystalline rubrene. The importance of short contacts and molecular distances, which is often overlooked as a parameter to consider and optimize when choosing materials for excitonic devices, is emphasized.
有机光电探测器和光电器件的效率受到激子扩散的强烈限制，特别是对于受体材料而言。尽管激子扩散的机制已经得到充分确立，但其与实际系统中分子组织的相关性却很少受到关注。在本报告中，利用波长依赖光电流光谱对有机单晶界面进行了探测，并使用X射线衍射解析了其晶体结构。所有系统均呈现出动态光响应，响应速度快于500毫秒，波长可达650纳米。建立了取代丁基苝二酰亚胺（PDIB）中分子组织与有利激子扩散之间的关系。这通过一组具有不同层内和层间距离以及短接触的PDIB及其对光响应的影响得到了证明。鉴于沿相同堆叠方向（3.4 - 3.7 Å）以及跨平行堆叠（2.5 Å）的苝二酰亚胺核心之间的短堆积距离，这些PDIB中的单线态激子可以遵循Förster和Dexter激子扩散机制，其中Dexter型机制对于层间激子扩散具有特殊相关性。然而，在取代的PDIB中响应达到最大值，其中通过强层间接触形成二维渗流网络，使得PDIB的初级激子能够高效地到达与结晶红荧烯的分裂界面。强调了短接触和分子距离的重要性，在为激子器件选择材料时，这一参数常常被忽视，而未被视为需要考虑和优化的因素。
