Energy-Level Alignment of a Hole-Transport Organic Layer and ITO: Toward Applications for Organic Electronic Devices

Abstract

2,2',6,6'-Tetraphenyl-4,4'-dipyranylidene (DIPO-Ph) was grown by vacuum deposition on an indium tin oxide (ITO) substrate. The films were characterized by atomic force microscopy as well as synchrotron radiation UV and X-ray photoelectron spectroscopy to gain an insight into the material growth and to better understand the electronic properties of the ITO/DIPO-Ph interface. To interpret our spectroscopic data, we consider the formation of cationic DIPO-Ph at the ITO interface owing to a charge transfer from the organic layer to the substrate. Ionization energy DFT calculations of the neutral and cationic species substantiate this hypothesis. Finally, we present the energetic diagram of the ITO/DIPO-Ph system, and we discuss the application of this interface in various technologically relevant systems, as a hole-injector in OLEDs or as a hole-collector interfacial layer adjacent to the prototypical OPV layer P3HT:PCBM.

Organic Monomolecular Layers Enable Energy-Level Matching for Efficient Hole Transporting Layer Free Inverted Perovskite Solar Cells

“…To this end, organic monomolecular layer (ML) materials, which can regulate the E F of electrodes, have been widely used in organic electronics. − Despite this property, organic ML has rarely been utilized to fabricate high-efficiency HTL-free PSCs. On one hand, in the PSC area, the energy-level alignment at the electrode/HTL interface has been often oversimplified in previous reports . On the other hand, different from organic materials, the strong ionic nature of perovskites may eliminate the impact of an organic ML on the E F of the electrode by strong chemical interaction with it .…”

“…On one hand, in the PSC area, the energy-level alignment at the electrode/HTL interface has been often oversimplified in previous reports. 17 On the other hand, different from organic materials, the strong ionic nature of perovskites may eliminate the impact of an organic ML on the E F of the electrode by strong chemical interaction with it. 18 Up to now, the feasibility of using an organic ML in constructing efficient HTL-free PSCs is yet unclear and rarely reported.…”

X-ray microscopic investigation of molecular orientation in a hole carrier thin film for organic solar cells

“…[29,31] In addition, the ITO/DIPO-Ph4 interface has already been structurally and electronically described. [32] As interfacial layer, DIPO-Ph4 layer will act as a hole-transport and an electron blocking layer. Concerning the solar cell stack, it is worth to note that on top of the DIPO-Ph4 layer a thin layer (5 nm) of PEDOT:PSS was deposited to prevent the organic solvent of P3HT:PCBM deposition to modify the DIPO-Ph4 morphology.…”

“…Besides, less number of holes are recombined to be collected at the ITO electrode due to the electron blocking effect with the DIPO-Ph4 layer. [32] As hole transport layer and compared to PEDOT:PSS, our organic layer increases the efficiency of charge collection at the ITO anode. On thick DIPO-Ph4, it is worth to notice that the fill factor increases significantly despite the surface mounds.…”

Application of reduced graphene oxide as the hole transport layer in organic solar cells synthesized from waste dry cells using the electrochemical exfoliation method

“…9,10 However, the hole transport layer (HTL) is equally important to obtain high PV performance and long-term stability. 11 Furthermore, the HTL has various benefits, such as modifying the energy level alignment of the ITO and the active layer, 12 minimizing charge recombination, 13 passivizing surface defects, minimizing leakage current, 14 and regulating the morphology of the active layer of the OSCs. 15 Well-known HTLs that are traditionally used in OSCs include poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer, which exhibits the required criteria of HTLs in terms of work function, water solubility, and transmittance.…”