Surface Modification of Indium‐Tin‐Oxide Via Self‐Assembly of a Donor‐Acceptor Complex: A Density Functional Theory Study

Abstract

The authors study at the density-functional theory level the modification of the electronic structure of the ITO surface upon self-assembly of a monolayer of t-butyl carbazole-substituted phosphonic acid molecules and subsequent p-doping. The results of the calculations point to the existence of two channels for charge transfer. These channels can enhance hole injection between ITO and a hole-transport overlayer through the chemically-modified interface.

Imaging of morphological changes and phase segregation in doped polymeric semiconductors

“…Recent scientific efforts towards this milestone focus on the use of dopant molecules to improve the electrical transport characteristics of light emitting diodes and solar cells [1][2][3][4]. Doping has been also demonstrated to be critical for tuning the carrier injection properties at metal-semiconductor interfaces, potentially leading to full control over device parameters [5][6][7]. Spatially controlled positioning of dopants can be used to tune injection [6,8], improve carrier drift/diffusion in transport layers [9][10][11] and also charge separation at heterojunctions [12].…”

Work function reduction by a redox-active organometallic sandwich complex

“…Despite the limitations of PBE, it has been used to describe charge transfer systems, such as perylene-3,4,9,10-tetracarboxylicdiimide (PTCDI), 31 perylene-3,4,9,10tetracarboxylic dianhydride (PTCDA) 32 and C 60 33 on ZnO, as well as a donor-acceptor complex of tetrafluorotetracyanoquinodimethane (F 4 -TCNQ) with t-butyl carbazole-phosphonic acid modified ITO. 34 In these earlier works, the work function changes and charge-transfer characters have been calculated at the PBE level and good agreement with experiment has been reported. [31][32][33] In the gold calculations, a 2 × 2 × 1 Monkhorst-Pack k-point grids was used for geometry optimizations for all unit cells, while 6 × 6 × 1, 3 × 6 × 1, and 3 × 3 × 1 Monkhorst-Pack k-point grids were used for self-consistent total-energy calculations for the smallest, remarkably similar, with differences on the order of 0.01 |e| (see Table S6 in the Supporting Information; note that the Gaussian smearing method was used for the isolated systems and only the Γ-point was employed in such calculations).…”

Electrode Work Function Engineering with Phosphonic Acid Monolayers and Molecular Acceptors: Charge Redistribution Mechanisms

“…Proposed models to describe the complex inorganic−organic and organic−organic interface processes involve integer charge (electron) transfer (ICT), [6,13] induced density of interface states (IDIS), [14] polarization, [15,16] and/or the formation of charge transfer complexes (CTCs). [10,17,18] In the first experimental work reporting the sequential formation of a π-conjugated organophosphonate monolayer on an inorganic conductor, followed by deposition of a strong electron acceptor, Hanson et al [19] presumably p-doped the monolayer of quarterthiophene phosphonic acid (4TPA) covalently bound to an indium-tin oxide (ITO) anode surface. They found very high current densities in light emitting devices using the modified ITO anode and assumed that the F 4 TCNQ molecules, as pdopants, form CTC's with the 4TPA molecules, leading to improved charge injection across that interface.…”

“…They found very high current densities in light emitting devices using the modified ITO anode and assumed that the F 4 TCNQ molecules, as pdopants, form CTC's with the 4TPA molecules, leading to improved charge injection across that interface. In a later theoretical work, Li et al [17] investigated the impact of F 4 TCNQ on an ITO surface modified by a monolayer of a di-tert-butyl-carbazole-substituted phosphonic acid (t-BCPA, molecular structure shown in Figure 1b) using density functional theory (DFT) calculations. They assumed that F 4 TCNQ could either form a CTC with the carbazole fragments of the t-BCPA monolayer, or adsorb directly onto the ITO surface while forming a side-by-side configuration with the t-BCPA molecules; in both cases a substantial increase in work function was predicted by the calculations.…”