Photoelectron spectroscopy study of systematically varied doping concentrations in an organic semiconductor layer using a molecular p-dopant

Abstract

We investigate the doping behavior of the strongly electron accepting molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane coevaporated with the host molecule N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine by photoemission spectroscopy and conductivity measurements. Using interface resolved measurements, we compare the alignment on different substrates and investigate the effects of varying doping concentrations on the Fermi level position. We find that at high doping concentrations the Fermi level gets pinned at the exponentially decaying tail of the highest occupied molecular orbital and compare these results with different dopants and host molecules. The measurement of the doping dependent space charge layer thickness yields information on the amount of free charge carriers and thereby the efficiency of the doping.

Optical measurement of doping efficiency in poly(3-hexylthiophene) solutions and thin films

“…Specialized methods such as capacitance-voltage measurements, 7,15 photoelectron spectroscopy measurements, 16,17 or modeling of transistor pinch-off voltages shifts 18 have been developed to address this problem.…”

Energetics at Doped Conjugated Polymer/Electrode Interfaces

“…Several studies claim that effective p-type doping occurs when the dopant lowest unoccupied molecular orbital (LUMO) level is deeper than the host highest occupied molecular orbital (HOMO) level in order to realize integer charge transfer. [9,17,18] 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) with its LUMO located at ~ 5.24 eV [19] should then be a strong p-type dopant upon mixing with the host polymers [9,17] (crystalline) regioregular poly(3-hexylthiophene) (rr-P3HT, HOMO ~ 4.65 eV) and (amorphous) poly [2,3- Several studies find that energy level alignment at organic/electrode and organic/organic interfaces plays a critical role in multilayer stack device, nearly dominating the performance. [20][21][22][23][24] Typically, the energy level alignment of such interfaces follows the trends predicted by the so-called integer charge transfer (ICT) model, i.e.…”

Ultralow Doping in Organic Semiconductors: Evidence of Trap Filling

“…Doping ratios used for devices and fundamental investigations usually range from 10 -2 to 10 -1 dopants per matrix molecule [18][19][20][21][22][23][24]. However, typical trap densities in disordered organic semiconductors are estimated to be in the range of 10 The doping studies were conducted on C 60 (Sigma Aldrich, 99.9% purity) and the n-dopant…”