In the past few years, we have fabricated nanoscale La0.7Sr0.3MnO3 periodic arrays with unique optical and magnetic
properties successfully. These periodic patterns were made by La0.7Sr0.3MnO3 resist that can be developed under a
nontoxic and environmental friendly manner using pure water. The resist is also capable to exhibit both positive and
negative resist behaviors depending on the electron beam dosage. Thus, these special characteristics are used to fabricate
and tune periodic structure thin film having controlled optical reflectance properties in the wavelength of 300 nm to 800
nm with one fixed design electron beam pattern by simply changing the electron beam dosage only. Additionally, the
magnetization of La0.7Sr0.3MnO3 patterns can be enhanced by post sintering the sample at 900 °C after electron beam
irradiation. Therefore, our study provides a one-step, simple, and convenient alternative technique for the fabrication of
tunable optical structure and nanoscale magnetic patterns, which form the building blocks for the study of optoelectronic
and magnetic devices in nanoscale periodic arrays.
In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene)/TiO2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO2 nanorods surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 2.2 % under simulated A.M. 1.5 illumination (100mW/cm2) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.
The solution processable poly(3-hexylthiophene)(P3HT)/TiO2-nanorod hybrid material for solar cells has been
successfully demonstrated. A critical issue for using hybrid heterojunction concept is the interface properties which
affect the exciton separation efficiency and bi-carrier transport. To improve the interface properties, we replace the
insulating surfactant on TiO2 nanorod surface with a more conductive oligomer, carboxylate terminated 3-hexylthiophene (P3HT-COOH). The enhancement of exciton separation efficiency due to better organic-inorganic
interfacial compatibility can be obtained. The electron mobility for transporting in the TiO2 network is improved. A
power conversion efficiency has been increased 3 times by using this new hybrid material without optimization as
compared with the hybrid without P3HT-COOH modification.
This paper aims to propose a 3D nanostructured organic-inorganic hybrid photovoltaic device based on the ZnO
nanostructures/poly(3-hexylthiophene)(P3HT):TiO2 nanorods hybrids by solution processes at low temperature. An array
of ZnO nanorods with a larger size of ~50 nm in diameter and ~180 nm in length are grown to provide direct pathways
for efficient charge collection. TiO2 nanorods with a size of ~5 nm in diameter and ~20-30 nm in length are incorporated
into polymer to facilitate charge separation and transport by providing increased interfacial area and more effective
transport pathway. The device performance with the inclusion of TiO2 nanorods exhibits a seven times increase in the
short circuit current with respect to that without TiO2 nanorods.
The mechanisms of exciton dissociation and migration in the conjugated polymer
(poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene)(MEH-PPV) / CdSe nanoparticle
hybrid materials were investigated by steady-state and time-resolved photoluminescence spectroscopy.
Rapid exciton dissociation at the nanoparticle/polymer interfaces leading to quenching of the
photoluminescence efficiency
η and shortening of the measured lifetime τPL is observed. The excitons
which contribute to the remaining luminescence in polymer will migrate to the lower energy sites with
longer conjugated sequences in the composites. The result is evident from the observations of a redshift
of the photoluminescence peak positions, a progressive decrease of the Huang-Rhys factor S and an
increase in the nature radiative lifetime τR with increasing CdSe nanoparticle content. The solar cell
based on the MEH-PPV / CdSe nanoparticle hybrid materials are fabricated and the transport
mechanism of the device will also be discussed.
Photovoltaic devices based on the conjugated polymer (poly(2-methoxy-5-(2'-ethyl)(hexyloxy)1,4-phenylenevinylene)
(MEH-PPV) / TiO2 nanorods hybrid materials are investigated. It is found that efficient charge separation occurs at the
interfaces of MEH-PPV/ TiO2 nanorods, accompanying with a significant quench in the photoluminescence (PL)
intensity and a decrease of PL lifetime with increasing TiO2 nanorod concentrations. The device based on the MEHPPV/
TiO2 nanorod hybrid material shows power efficiency about 2.2% at the incident light with a wavelength of 565
nm. The transport properties of the solar cells are further investigated and discussed.
The significance of surface states in nano-structures is studied using CdS nanoparticles. Spectral features like peak red-shift due to organic capping and influence of surface states have been observed. The pronounced enhancement of emission from surface states can be dominant with certain modiciation of CdS nanoparticles. Spectral behaviors of electroluminescence in different temperature are also studied.
The fabrication of CdS-nanoparticle light emitting diodes (LEDs) on Si and their properties at room temperature and variant temperatures are reported. Due to passivation of p- hydroxyl thiophenol group around nanoparticles, 86-meV spectral shift of free exciton transition at room temperature is observed. Controlled conditions for the preparation of CdS-nanoparticle LED such as heat treatment and/or with oxygen-rich environment are found to have significant influences on emission spectra. Radiative recombination of carriers trapped in oxygen-impurity level of 273 meV presents in samples prepared in oxygen-rich environment. Coalescence of nanoparticles into bulk form also occurs to contribute to increased magnitude of luminescence. Spectral behaviors of electroluminescence with varied temperature are studied.
We report that electroluminescence (EL) at Si bandgap energy is significantly enhanced from the nano-structured metal- oxide-semiconductor (MOS) devices on silicon. The nano- structure is constructed by inserting SiO2 nanoparticles with the size of 12 nm in the oxide layer. The measured EL efficiency of the nano-structured MOS devices is enhanced to be near 10-4, which exceeds the limitation imposed by the indirect bandgap nature of silicon. We also observed the nearly lasing behaviors such as the threshold and resonance modes in the EL characteristics. The enhanced EL efficiency is attributed to simultaneous localization of electrons and holes to form exciton by nano-structure. This causes the process of the phonon-assisted radiative recombination of electron-hole pair more like two-particle (exciton-phonon) collision than three-particle (electron- hole-phonon) collision.
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