Oligo- and polythiophene/ZnO hybrid nanowire solar cells.
ABSTRACT We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell. End-functionalized oligo- and polythiophenes were grafted onto ZnO nanowires to produce p-n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and electron microscopy to determine the optoelectronic properties and to probe the morphology at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, J(sc) = 0.32 mA/cm(2), V(oc) = 0.4 V, and a FF = 0.28 under AM 1.5 illumination with 100 mW/cm(2) light intensity. These individual test structures will enable detailed analysis to be carried out in areas that have been difficult to study in bulk heterojunction devices.
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ABSTRACT: The work function (WF) of ZnO is modified by two types of dipole-bearing phenylphosphonate layers, yielding a maximum WF span of 1.2 eV. H3CO-phenyl phosphonate, with a positive dipole (positive pole pointing outwards from the surface), lowers the WF by ∼350 meV. NC-phenyl phosphonate, with a negative dipole, increases the WF by ∼750 meV. The WF shift is found to be independent of the type of ZnO surface. XPS data show strong molecular dipoles between the phenyl and the functionalizing (CN and OMe) tail groups, while an opposite dipole evolves in each molecular layer between the surface and the phenyl rings. The molecular modification is found to be invariant to supra-bandgap illumination, which indicates that the substrate's space charge-induced built-in potential is unlikely to be the reason for the WF difference. ZnO, grown by several different methods, with different degrees of crystalline perfection and various morphologies and crystallite dimensions, could all be modified to the same extent. Furthermore, a mixture of opposite dipoles allows gradual and continuous tuning of the WF, varying linearly with the partial concentration of the CN-terminated phosphonate in the solution. Exposure to the phosphonic acids during the molecular layer deposition process erodes a few atomic layers of the ZnO. The general validity of the treatment and the fine-tuning of the WF of treated interfaces are of interest for solar cells and LED applications.Physical Chemistry Chemical Physics 03/2014; · 3.83 Impact Factor
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ABSTRACT: Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of “bottom-up” growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. We conclude with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.Advanced Materials 03/2014; · 14.83 Impact Factor
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ABSTRACT: Conjugated polymer-semiconductor quantum dot (QD) composites are attracting increasing attention due to the complementary properties of the two classes of materials. We report a convenient method for in situ formation of QDs, and explore the conditions required for light emission of nanocomposite blends. In particular we explore the properties of nanocomposites of the blue emitting polymer poly[9,9-bis(3,5-di-tert-butylphenyl)-9H-fluorene] together with cadmium sulphide (CdS) and cadmium selenide (CdSe) precursors. We show the formation of emissive quantum dots of CdSe from thermally decomposed precursor. The dots are formed inside the polymer matrix and have a photoluminescence quantum yield of 7.5%. Our results show the importance of appropriate energy level alignment, and are relevant to the application of organic-inorganic systems in optoelectronic devices.Physical Chemistry Chemical Physics 04/2014; · 3.83 Impact Factor
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Lawrence Berkeley National Laboratory
Oligo and Poly-thiophene/Zno Hybrid Nanowire Solar Cells
Briseno, Alejandro L.
Lawrence Berkeley National Laboratory
Oligo, Polythiphene, Zno, Hybrid Nanowire
LBNL Paper LBNL-3396E
Nano Letters , DOI 10.1021, nl9036752, pg 334-340, 12/15/2009
We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell.
End-functionalized oligo- and polythiophenes were grafted onto ZnO nanowires to produce p-
n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and
electron microscopy to determine the optoelectronic properties and to probe the morphology
at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved
characteristics with efficiencies as high as 0.036percent, Jsc = 0.32 mA/cm2, Voc = 0.4 V, and
a FF = 0.28 under AM 1.5 illumination with 100 mW/cm2 light intensity. These individual test
structures will enable detailed analysis to be carried out in areas that have been difficult to study
in bulk heterojunction devices.
Oligo- and Poly-thiophene/ZnO Hybrid Nanowire Solar Cells
Alejandro L. Briseno, Thomas W. Holcombe, Akram I. Boukai, Erik C. Garnett, Steve
W. Shelton, Jean J. M. Fréchet*, Peidong Yang*
Department of Chemistry, University of California, Berkeley, California 94720, and
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley,
Email: email@example.com; firstname.lastname@example.org
We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar
cell. End-functionalized oligo- and poly-thiophenes were grafted onto ZnO nanowires to
produce p-n heterojunction nanowires. The hybrid nanostructures were characterized via
absorption and electron microscopy to determine the optoelectronic properties and to
probe the morphology at the organic/inorganic interface. Individual nanowire solar cell
devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, Jsc=
0.32 mA/cm2, Voc= 0.4 V, and a FF= 0.28 under AM 1.5 illumination with 100 mW/cm2
light intensity. These individual test structures will enable detailed analysis to be carried
out in areas that have been difficult to study in bulk heterojunction devices.
Hybrid solar cells composed of organic semiconductors
1 and inorganic
nanostructures 2 are an area of immense study as they are alternatives to organic bilayer 3
and bulk heterojunction device structures.4,5 The organic/inorganic hybrid system 6-9 has
opened new opportunities for the development of future generation solar cells, new
device technologies, and a platform to study three-dimensional morphology.10 A
multitude of concepts have been demonstrated by combining p-type donor polymers with
n-type acceptor inorganic nanostructures such as CdSe,6,7,11 TiO2,8-10,12-15 and ZnO.8-10,14
One-dimensional (1-D) inorganic semiconductor nanostructures are among some of the
most attractive nanomaterials for solar cell devices because they provide a direct path for
charge transport.2 Other advantages include high carrier mobilities, solution
processability, thermal and ambient stability, and a high electron affinity necessary for
charge injection from the complementary organic donor material. ZnO nanowires are an
example of this class of materials that have been used for hybrid solar cells.8-10,14,16
Poly(3-hexylthiophene) (P3HT)/ZnO nanowire composite solar cells are benchmark
systems that have attained power conversion efficiencies ranging from 0.02 to 2%.9,16,17
In spite of the vast efforts in this area of research, solar cells based on hybrid composites
have yielded efficiencies only close to those of organic bilayer devices and significantly
less than organic bulk heterojunction solar cells. Knowledge regarding interfacial charge
separation and/or transport in hybrid nanowire devices is only partly understood.10,17 If
this class of materials is to play a part in the future of next generation solar cells, then
there must be an improved fundamental understanding of the organic/inorganic interface
in order to improve power conversion efficiencies. While nanowire array and bulk
inorganic/organic blend devices are technologically relevant, their electrical properties
depend on nanostructure size, uniformity, crystallinity, phase segregation, interfacial
interactions, mobility, trap density and many other factors. For macroscopic devices,
these parameters can vary significantly over the active area, making it difficult to
attribute any change in performance to a particular phenomenon. Single nanowire
devices allow for more precise control over and characterization of the properties listed
above, greatly reducing the uncertainty in data interpretation.
In this study, we utilize end-functionalized p-type oligo- and poly-thiophene to
chemically graft the organic component to an n-type ZnO nanowire, producing a p-n
core-shell nanowire from which we subsequently fabricated a single nanowire solar cell.
We end-functionalized P3HT and quaterthiophene with a phosphonic ester and acid,
respectively, and self-assembled the semiconductors onto the ZnO surface in the solution
phase to yield organic shells with thicknesses of about 5-20 nm. We present results on the
synthesis and characterization of the organic/ZnO composites, high-resolution
transmission electron microscopy (TEM) of the organic/ZnO interface, as well as results
on the photovoltaic characteristics of individual nanowire devices. The nanowire devices
yield low efficiencies of about 0.03%, but provide an effective platform for isolating and
studying the many phenomena that affect bulk hybrid solar cell performance.
ZnO nanowires were prepared via solution and vapor-phase synthesis as previously
reported.18-20 Both methods can produce high-quality, single crystalline nanowires with
lengths of several microns and diameters ranging from 30-100 nm. Regioregular P3HT
was prepared from 2-bromo-3-hexyl-5-iodo thiophene through the Grignard metathesis
(GRIM) reaction21 to afford a bromine-terminated polymer with a molecular weight of
~7000 Da as determined via MALDI-TOF. End-functionalization was carried out by
reacting P3HT-Br with butyllithium and then diethylchlorophosphate to yield a
phosphonic ester. Didodecylquaterthiophene (QT) was end-functionalized via a similar
pathway, however, the ester was subsequently hydrolyzed to afford a phosphonic acid.
We note that the P3HT-phosphonic ester was not hydrolyzed to the phosphonic acid since
the reaction conditions using trimethylsilyl bromide degrade the properties of P3HT.
Figure 1 shows the synthetic steps towards functionalization of the two organic materials.
Details of the synthesis and characterization are included in the supporting information.
We obtained core-shell nanowires by stirring a suspension of ZnO nanowires in a 2
mg/ml chlorobenzene solution of the respective functionalized organic components
overnight. The composite materials were purified by centrifugation followed by removal
of the supernatant containing excess organic component. THF was added to the
precipitated nanowires and the purification step was repeated an additional three times.
No efforts were made to vary the concentration of the oligothiophene in organic solvent.
However, we did substitute THF and chloroform for chlorobenzene, and similar results
were obtained. Large-scale quantities (~20 mg) of functionalized nanowires were
prepared from both organic components. Dry powders were stored in a nitrogen box to
prevent oxidation. ZnO/P3HT composites are light purple in color while the ZnO/QT
composites are yellow (Figure 2). The hybrid nanowires can be easily re-dispersed by
sonicating in methanol for 5-10 seconds.
We verified the grafting of oligothiophenes onto ZnO nanowires via UV absorption
spectroscopy. Arrays of ZnO nanowires on quartz substrates were employed in this
experiment because light scattering prevented solutions of the hybrid nanowires from
yielding quality spectra. Grafting of the organic component onto ZnO arrays were carried