Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning

Abstract

The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach.

Energy-Level Engineering at ZnO/Oligophenylene Interfaces with Phosphonate-Based Self-Assembled Monolayers

“…This work function increase is a consequence of Fermi-level pinning at the lowest unoccupied density of states of the L4P-sp3 layer, which leads to electron transfer to the overlayer and thus the Φ increase. 20 Figure 3b−d shows spectra of the valence region of the unmodified, PyPA-modified, and L4P-sp3/PyPA-modified ZnO surface (with increasing L4P-sp3 coverage), respectively. The extended valence region spectrum of the PyPA-modified ZnO surface (red line in Figure 3b) is characterized by two relatively broad emission bands, which are labeled as A′ and B′ in Figure 3b and are located at 6.45 and 10.60 eV BE, respectively.…”

Theory of Excitation Transfer between Two-Dimensional Semiconductor and Molecular Layers

“…Here, only a single-excitation basis for molecular excitons is considered, which is a reasonable assumption since the molecular lifetimes in such hybrid systems (tens to hundreds of picoseconds [6]) are smaller or of the same order as the mean excitation transfer times from the electrically pumped substrate into the organic layer, as detailed in Sec. IV.…”

“…A potential advantage of hybrid inorganic-organic systems over their individual constituents is that a synergistic combination can lead to enhanced optoelectronic properties and tunable functionality [1][2][3][4][5][6][7][8][9]. Typical components include organic materials such as organic dye molecules, and inorganic semiconductor nanostructures such as a quantum well (QW) or a semiconductor surface [10][11][12][13][14].…”

Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer

“…A prime example are systems of optically active molecules at inorganic surfaces; these so-called hybrid inorganic/organic systems (HIOS) represent a very promising material class in optoelectronics. [1][2][3][4] Typically, the corresponding organic molecules are strongly anisotropic in shape and are characterized by complex charge distributions, often dominated by a quadrupole moment. 5 By manipulating the orientational structure of such organic layers it is possible to tune the efficiency of the charge carrier transport 6 and thus to optimize the efficiency of the hybrid system.…”