WIEDZA TECHNICZNA

1
WIEDZA TECHNICZNA
Wyklad wygloszony w ramach projektu
Wzmocnienie znaczenia Politechniki Krakowskiej w
ksztalceniu przedmiotów scislych i propagowaniu
wiedzy technicznej w regionie
Projekt wspólfinansowany przez Unie Europejska w
ramach Europejskiego Funduszu Spolecznego
2
Procesy electronowe w cienkich warstwach
poliazometyn

• Introduction
• Chemical structure of polyazomethines
• Optical transitions
• Electronic structure
• Vibronic progression
• Doped polyazomethine thin films
• Photoluminescence (PL)
• Conclusions

3
Organic materials
Promising in organic electronics as
electroluminescent organic light-emitting diode
(OLED), display and switching devices, solar
cells, sensors, etc., and replacing inorganic
semiconductors.

• Two classes of organic semiconductors
• low molecular weight materials (molecular
  compounds),
• high molecular weight materials polymers.

Among polymers aromatic polyazomethines (Schiff
bases) being conjugated polymers with N atoms in
the backbone.
4
Preparation
Polyazomethine thin films are prepared via
polycondensation reaction of terephaldehyde
(TPA) and one of aromatic diamines using various
methods, such as chemical vapor deposition (CVD),
thermal vacuum evaporation (TVE) and spin-coating
technique. The polycondensation reaction in the
case of the simplest polyazomethine, i.e.
poly(1,4-phenylene-methylidynenitrilo-1,4-phenylen
enitrylomethylene) (PPI), may be written as
TPA
p-phenylenediamine (PPDA)
5
More complex polyazomethines

• Using other diamines, i.e. 7,2-diamino-fluorene,
  1,1-biphenyl-3,3,4,4-tetramine and
  3-amino-4-(1-naphthyldiazenyl)phenylamine (fat
  brown RR), one gets new polyazomethines, namely
• poly(1,4-phenylene-methylidynenitrylo-2,7-9H-fluo
  rene-nitrylomethylidyne), abbreviated as FPI
• poly(1,4-phenylene-methylidynenitrylo-1,1-biphen
  yl-3,3,4,4-phenylene-methylidyne-imine),
  abbreviated as BPI
• poly(1,4-phenylene-methylidynenitrylo-1,3-phenylen
  e-(4-(1-naphthylodiazenyl)-nitrylomethylidyne),
  abbreviated as PNAPI.

6
Chemical structure of polyazomethines (PAMs)
7
Optical spectra of polyazomethines
-------------------- PAM Eg (eV) -----------------
--- PPI 2.35 FPI 2.03 BPI 1.87 PNAPI 1.80
8
Lorentz oscillator model

• e1 ie2

,


9
Electronic structure of PPI
reflecting interactions of benzene and ethylene
molecular orbitals
LUMO
L localized states D delocalized states Ex
exciton states A1 p-p transition LP- lone
electron pair
HOMO
10
Doped PPI films
Doping in the iodine vapor (I2)
Doping with FeCl3 (during CVD process)
11
Doped PPI films optical spectra
12
Formation of the polaron state
Undoped PPI
Doped PPI
13
Photoluminescence (PL)
14
Conclusions
The electronic properties of the presented
polyazomethine thin films resemble in many
respects those of poly(p-phenylene-vinylene)
(PPV) which is a very promising material for
applications in organic electronics. Examining
various properties of PAMs, feasibility of future
applications of this polymer family should be
rather considered in view of their blending with
other polymers or molecular materials to produce
volume p-n junctions - basic elements of
photovoltaic structures. On the other side,
their chemical and electronic structure may be
exploited for preparation of layered devices
based, for example, on PAM/fullerene p-n
junctions. In view of potential applications of
various structures containning polyazmomethines,
further studies are desirable, involving
optimization of technology, detailed knowledge of
electronic structure and processes occuring at
interfaces, and, finally, the design and
fabrication of long-time operating devices.