We have developed an electrospraying technique inspired from Marangoni flow seen in nature. We demonstrate our ability to synthesise highly crystalline uniform perovskite thin films with enhanced coverage and high absorption. Due to a difference in the vapour pressure of DMSO and NMP, a gradient force is developed that helps in propagating the incoming precursor droplet to coalesce and merge with other droplets thus inducing a dynamic self-assembly within the thin film. This results in thin films with high uniformity and good morphological and topological characteristics, that collectivelty resulted in a respectable PCE of greater than 14%. Optical studies are conducted in parallel to better understand the energy phase space of perovskite crystals. The high temperature tetragonal phase showed a high recombination rate of 180 ns, ideal for photovoltaic performances, while the low temperature measurements reveal considerable complexity in spectral and dynamic properties that demand further invesgtiation.
We have developed an all-optical method to control the in- and out-of-plane spatial orientation of nematic liquid crystal
(NLC) molecules by leveraging the highly localized electric fields produced in the near-field regime of gold nanoparticle
(AuNP) layers. A 1-2 micron thick NLC film is deposited on a close-packed drop-cast AuNP layer, excited with tunable
optical sources and the transmission of white light through it analyzed using polarization optics as a function of incident
light wavelength, excitation power and sample temperature. Our findings, supported by simulations using discrete-dipole
approximations, establish the optical switching effect to be repeatable, reversible, spectrally-selective, operational over a
broad temperature range, including room temperature, and requiring very small on-resonance excitation intensity (0.3
W/cm2). For the case of the in-plane switching we have additionally demonstrated that controlling the incident excitation
polarization can continuously vary the alignment of the NLC molecules, allowing for grayscale transmission.
The ability to control and direct self-assembly of nanostructures into specific geometries with new functionalities, while
preserving their original optical and electronic properties, is an attractive research endeavor. We have fabricated liquid
crystal (LC) based matrices into which chemically synthesized nanostructures of varied morphologies and compositions
are uniformly dispersed. Using high resolution spatially- and time-resolved scanning photoluminescence (PL)
measurements, we have demonstrated directed nanoparticle assembly and manipulation in situ. This includes (a)
directional assembly and electric field modulated re-orientation of disk-shaped gallium selenide nanoparticles using a
nematic LC matrix, and (b) spectral modulation of chemically synthesized core shell CdSe/ZnS quantum dots (QDs)
embedded in a cholesteric liquid crystal (CLC) matrix. Our work opens up the possibility of designing new QD based
optical devices where spatial control of orientation, wavelength and polarization of the embedded QDs would allow
great flexibility and added functionalities.
A number of methods to reduce the cost of solar power generation have been developed over the last few decades.
Recently, research and development in the area of Luminescent Solar Concentrators (LSCs) have shown that these
devices are capable of significantly reducing the price of solar energy. We propose using near infra-red (NIR) quantum
dots (QDs) as luminescent media in the LSC. Our results demonstrate that LSCs designed with NIR QDs can generate
over twice the energy as the ones using their visible counterparts.
Quantum dot (QD) luminescent solar concentrator (LSC) uses a sheet of highly transparent materials doped with
luminescent QDs materials. Sunlight is absorbed by these quantum dots and emitted through down conversion process.
The emitted light is trapped in the sheet and travels to the edges where it can be collected by photovoltaic solar cells. In
this study, we investigate the performance of LSCs fabricated with near infrared QDs (lead sulfide) and compared with
the performance of LSCs containing normal visible QDs (CdSe/ZnS), and LSCs containing organic dye (Rhodamine B).
Effects of materials concentrations (related to re-absorption) on the power conversion efficiency are also analyzed. The
results show that near infrared QDs LSCs can generate nearly twice as much as the output current from normal QDs and
organic dye LSCs. This is due to their broad absorption spectra. If stability of QDs is further improved, the near infrared
QDs will dramatically improve the efficiency of LSCs for solar energy conversion with lower cost per Wp.
In recent years the dispersion and directed assembly of nano-particles in liquid crystal media has proved an interesting
field for investigation and one that may yield new hybrid materials for optical applications and fundamental research. In
this paper, we investigate the dispersion of quantum dots in different liquid crystal phases, looking at aggregation and
pattern formation. Quantum dot self-assembly in liquid crystals is dependent on particle surface properties and
concentration in the liquid crystal medium. By varying these parameters we observe some fascinating structures and
phase behavior using polarized optical microscopy and fluorescence microscopy.