A preview of this full-text is provided by Wiley.
Content available from Advanced Engineering Materials
This content is subject to copyright. Terms and conditions apply.
Enhanced Mechanical and Thermal Resistances of
Nanoimprinted Antireflective Moth-Eye Surfaces Based on
Poly Vinylidene Fluoride/TiO
2
Surface Nanocomposites
Alejandra Jacobo-Martín, Jaime J. Hernández,* Patricia Pedraz, Iván Navarro-Baena,
Miguel A. Monclús, Jon M. Molina-Aldareguia, and Isabel Rodríguez
1. Introduction
Nature has evolved to provide species with many different
surface functionalities to adapt to their living environment;
the study of the principles behind them are the subject of interest
and continuous study by many research groups.
[1]
Among the
most interesting functionalities are those related to the manipu-
lation of light at interfaces.
[2]
Reducing the light reflection and
improving the light transmission is crucial for the survival of
many nocturnal creatures
[3]
and it is also very helpful in many
man-made-products and consumer applications.
[4]
For instance,
more than 70% of the solar photovoltaics (PVs) panels have an
antireflective coating (ARC) on its surface for reducing optical
losses and increasing efficiency.
[5]
Currently, most of the
commercial silicon-based PVs use single-
layer ARC based on Si
3
N
4,
TiO
2
, or SiO
2
coatings, which suppress light reflections
through destructive interferences produced
at the layer’s interfaces.
[6]
The so called
quarter-wave ARC are optimized for a nar-
row range of wavelengths and incidence
angles. Multilayer coatings, combining
materials with variable refractive index,
overpass the AR performance of the sin-
gle-layer coatings in terms of omnidirec-
tionality and broadband antireflectivity
[7,8]
at expenses of a higher complexity
and material consumption during the
manufacturing process. A different
approach to implement antireflective (AR)
properties is based on texturization pro-
cesses to produce structured surfaces.
Traditionally, micrometer-sized inverted pyramidal or random
textures, which enhance light trapping through internal reflec-
tions, have been used.
[9]
Nevertheless, subwavelength AR nano-
structures, providing a graded refractive index, are a better option
for implementation on thin-film flexible PV and emerging light-
weight solar cells.
[9,10]
The main advantage of the latter approach
is that it provides reduction of reflections over a broad range of
spectral bandwidth and incidence angles
[11]
which is of great
importance to improve light harvesting, particularly in fixed solar
modules.
[12]
Moth eyes, covered by an array of subwavelength
nanocones, have been particularly inspiring as an antireflective
approach based on a graded refractive index.
[13]
Moth-eye AR
nanostructures have been directly etched onto Si,
[14]
or imple-
mented using metal oxide nanostructures such as TiO
2[15]
or
ZnO
[16]
to improve the efficiency of solar cells. The conventional
fabrication techniques, like dry/wet etching or physical and
chemical vapor deposition methods, and materials used allow
to achieve most of the requirements for AR coatings in PV appli-
cations: broadband and omnidirectional AR efficiency, durability
and possibly self-cleaning multifunctionality.
[7,12]
In addition to
these developments, there is still a need for cost effective and
large-scale fabrication methods of effective AR strategies.
Moth-eye AR nanopatterns can be produced at low cost with high
accuracy in polymeric materials using nanoimprint lithography
(NIL) techniques.
[17]
Furthermore, the technology can be up-
scaled by continuous NIL processes based on roll-to-roll (R2R)
fabrication to produce AR surfaces in large areas and at very
low costs as required for many PV technologies.
[18]
A. Jacobo-Martín, J. J. Hernández, P. Pedraz, I. Navarro-Baena,
I. Rodríguez
Madrid Institute for Advances Studies in Nanoscience (IMDEA
Nanoscience)
Ciudad Universitaria de Cantoblanco
C/ Faraday 9, Madrid 28049, Spain
E-mail: jaime.hernandez@imdea.org
M. A. Monclús, J. M. Molina-Aldareguia
Madrid Institute for Advanced Studies in Materials (IMDEA Materials)
C/ Eric Kandel 2, Tecnogetafe, Getafe, Madrid 28906, Spain
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adem.202100603.
DOI: 10.1002/adem.202100603
Herein, the fabrication of bioinspired moth-eye antireflective (AR) films based
on surface nanocomposites of poly vinylidene fluoride (PVDF) and TiO
2
nanoparticles produced in a single thermal nanoimprint lithography step is
described. The incorporation of nanoparticles enhances the mechanical and
thermal stability of the AR topography as demonstrated by nanoindentation
tests and
in situ
temperature-dependent grazing incidence X-ray scattering
measurements using synchrotron radiation. The effect of thermal annealing
and UV radiation on the degradation in the optical performance and durability
of the AR films is also evaluated in weathering tests. Improving the thermal
and mechanical behavior as well as the long-term durability of nanoimprinted
polymer AR films will significantly expand their potential for implementation
in solar devices.
RESEARCH ARTICLE
www.aem-journal.com
Adv. Eng. Mater. 2021,23, 2100603 2100603 (1 of 11) © 2021 Wiley-VCH GmbH