Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario, M5S 3E4, Canada.
Department of Physics, Yunnan University, Yunnan, 650091, China.
Adv Mater. 2017 Jun;29(24). doi: 10.1002/adma.201700414. Epub 2017 Apr 24.
An organic semiconductor thin film is a solid-state matter comprising one or more molecules. For applications in electronics and photonics, several distinct functional organic thin films are stacked together to create a variety of devices such as organic light-emitting diodes and organic solar cells. The energy levels at these thin-film junctions dictate various electronic processes such as the charge transport across these junctions, the exciton dissociation rates at donor-acceptor molecular interfaces, and the charge trapping during exciton formation in a host-dopant system. These electronic processes are vital to a device's performance and functionality. To uncover a general scientific principle in governing the interface energy levels, highest occupied molecular orbitals, and vacuum level dipoles, herein a comprehensive experimental research is conducted on several dozens of organic-organic heterojunctions representative of various device applications. It is found that the experimental data map on interface energy levels, after correcting variables such as molecular orientation-dependent ionization energies, consists of three distinct regions depending on interface fundamental physical parameters such as Fermi energy, work function, highest occupied molecular orbitals, and lowest unoccupied molecular orbitals. This general energy map provides a master guide in selection of new materials for fabricating future generations of organic semiconductor devices.
有机半导体薄膜是一种由一个或多个分子组成的固态物质。在电子学和光子学的应用中，需要将几种不同的功能有机薄膜堆叠在一起，以制造各种设备，例如有机发光二极管和有机太阳能电池。这些薄膜结处的能级决定了各种电子过程，例如这些结处的电荷输运、供体-受体分子界面上的激子离解速率以及主体-掺杂体系中激子形成时的电荷俘获。这些电子过程对于设备的性能和功能至关重要。为了揭示控制界面能级、最高占据分子轨道和真空能级偶极子的一般科学原理，在此对几十种具有各种器件应用代表性的有机-有机异质结进行了全面的实验研究。结果发现，在纠正了分子取向依赖性电离能等变量后，界面能级的实验数据图包含三个不同的区域，这取决于界面的基本物理参数，如费米能级、功函数、最高占据分子轨道和最低未占据分子轨道。这个通用的能量图为制造新一代有机半导体器件选择新材料提供了主要指导。
