Banca de QUALIFICAÇÃO: LEONARDO RODRIGUES MOREIRA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : LEONARDO RODRIGUES MOREIRA
DATA : 24/06/2024
HORA: 14:00
LOCAL: L204
TÍTULO:

Surface modification of indium tin oxide for work function tailoring using organic self-assembly monolayer

PÁGINAS: 40
RESUMO:

Organic solar cells (OSCs) with high efficiency have been developed during the past years
with a new generation of donor-acceptor molecular systems as active layers, as the Y6-PM6
bulk heterojunction (BHJ). The standard architecture for such devices is layered as i. glass
substrate, ii. transparent anode (hole collecting layer), iii. hole injection layer (typically
PEDOT:PSS), iv. charge separating active layer, v. electron injection layer (typically TiO2
and ZnO), and a low work function metal as cathode. Commonly, indium tin oxide (ITO) is
used as anode because of its high work function (φ =4.6–5.2 eV), while a metal with low work
function is used as cathode, typically, Al/Ca (φAl =4.06–4.26 eV and φCa =2.87 eV).
However, these low work function metals are prone to oxidation, leading to reduced durability
in ambient conditions. By preparing inverted cells, this problem can be circumvented. In this
configuration, ITO work’s function is decreased so it can function as cathode (up to φ =3.0
eV), while a high work function metal as Au and Ag (φAu =5.10–5.47 eV and φAg =4.26–4.74
eV) can play the role of anode. In order to achieve this goal, ITO can be functionalized on the
surface with highly polarizable inorganic or organic species. Based on previous reports, we
followed the route of evaporating cesium carbonate (Cs2CO3) on ITO, which would reduce
ITO’s work function by the formation of surface dipoles that attenuate the charge’s Coulomb
interaction on the surface. However, the Cs2CO3 presents low adhesion on the surface, except
when the glasses were submitted to thermal treatments at higher temperatures (>300◦C),
which otherwise led to damages in their morphology, as noted by scanning electron microscope
(SEM), leading to compromised conductivities. Another possibility is to functionalize the
surface of the ITO with organic polar molecules as self-assembled monolayers (SAM). We have
carried such procedure by choosing a series of polar and conjugated molecules functionalized
with carboxylic acid, a group that has high chemical affinity with ITO’s surface after its
O2 plasma activation. This resulted in ITOs with a wide range of work function values
while preserving their structural integrity and conducting characteristics. We investigated
the elemental composition of the ITO after O2 plasma treatment and SAM formation with
X-ray photoelectron spectroscopy (XPS) and the molecule adhesion to the structure by solid-
state Nuclear magnetic resonance (NMR) spectroscopy.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1734908 - FABIO FURLAN FERREIRA
Membro Titular - Examinador(a) Interno ao Programa - 2211564 - ANDRE PANIAGO LESSA
Membro Titular - Examinador(a) Externo ao Programa - 1544394 - PAULA HOMEM DE MELLO
Membro Suplente - Examinador(a) Externo ao Programa - 1762438 - JEAN JACQUES BONVENT
Membro Suplente - Examinador(a) Externo ao Programa - 1545089 - DANIEL ZANETTI DE FLORIO