Novel processing approaches for thin film solar and related technologies.

A growing population along with developing nations are increasing the demand for energy. The International Energy Agency forecasts a global electricity demand increase of 70 percent by 2040. This is an increase from nearly 18 TW to over 30 TW. The sun can be a great clean source of achieving this energy demand. Despite the large solar industry development, the market is still growing as solar energy only accounted for 0.87% of the global energy production in 2013. The opportunity exists to manufacture more affordable solar energy that can penetrate more of the global energy market. In this dissertation, a photonic-based manufacturing technique called intense pulsed light (IPL) was investigated to enhance the photovoltaic properties of CdTe, better understand the CdCl2 treatment used to create higher efficiency CdTe solar devices, enable the first sintering and efficiency enhancement of perovskite solar cell (PSC), and study the possible conversion of a stable 2D perovskite to a 3D perovskite. CdTe thin films grown by low temperature electrodeposition were treated for the first time with IPL. The low temperature electrodeposition growth resulted in films consisting of nanoparticles, with reduced melting point temperatures. In combination with the high temperature rise produced by the pulses of light, the lower melting temperature resulted in pores/voids being filled as well as enhanced grain growth. As a result, pin-holes and grain boundary recombination were diminished. Subsequently the fill factors of PV devices created using this technology significantly increased. In addition, the IPL also successfully improved the crystallinity in the CdTe films by photonically initiating the popular CdCl2 treatment. To understand the mystery behind the mechanism of the CdCl2 treatment, low temperature PL was utilized and new electrodeposition precursors resulting from the study improved device efficiencies. Photoactive perovskite CH3NH3PbI3 layers were successfully sintered with a novel IPL treatment with efficiencies exceeding 12%. The processing time was reduced to 2 ms, which was significantly faster than those from previous reports. Additionally, the average performance of the IPL-processed samples showed an improvement compared to the hot- plate-processed samples. This advance creates an exciting new method to quickly create dense layers of perovskite, eliminating the rate-limiting annealing step detrimental to industry adoption, and shows the first known occurrence of sintering in CH3NH3PbI3 perovskite particles. Lastly, the fast photonic processing of the IPL enabled the first conversion of a stable 2D perovskite structure into a 3D structure. This caused an band gap shift from 2.0 eV to 1.6 eV and showed the capabilities of band gap tuning enabled by the IPL. While this work is the first documentation of band gap tuning enabled by a photonic effect, it presents a possible inexpensive manufacturing technique that could use one material to create several different colors for the future development of pixel-based LED displays

Engine Oil Filter Test Stand

For the current test stand, the cleaning time is too long. There is no way to run different types of filters. These problems negates them from collecting more data to compare various filters in various sizes

Influence of Atmospheric Turbulence on Optical Communications using Orbital Angular Momentum for Encoding

We describe an experimental implementation of a free-space 11-dimensional communication system using orbital angular momentum (OAM) modes. This system has a maximum measured OAM channel capacity of 2.12 bits/photon. The effects of Kolmogorov thin-phase turbulence on the OAM channel capacity are quantified. We find that increasing the turbulence leads to a degradation of the channel capacity. We are able to mitigate the effects of turbulence by increasing the spacing between detected OAM modes. This study has implications for high-dimensional quantum key distribution (QKD) systems. We describe the sort of QKD system that could be built using our current technology.Comment: 6 pages, 5 figure

Agriculture Engine Oil Filter Test Stand

Our group worked on a project from Fleenor Manufacturing. This is a small company based out of Pella, Iowa owned by Jeff Fleenor. Jeff’s company focuses on creating solutions to unique problems across a wide spectrum of markets (Bruning et al., 2017; Yeggy et al., 2017). On this project, our client wanted to improve an existing test stand used for running oil filter tests, which can take up to four hours per test, and only test one filter size. We would like to minimize the time it takes to run a test while also enabling it to use different filters. Other companies are considering this technology because it can show them exactly how their products compare to others on the market. The completion of this project could help our client understand how OEM filters differ from aftermarket filters and how our client’s own design compares to all the other filters on the market

High-dimensional quantum cryptography with twisted light

Quantum key distributions (QKD) systems often rely on polarization of light for encoding, thus limiting the amount of information that can be sent per photon and placing tight bounds on the error that such a system can tolerate. Here we describe a proof-of-principle experiment that indicates the feasibility of high-dimensional QKD based on the transverse structure of the light field, allowing for the transfer of more than 1 bit per photon. Our implementation uses the orbital angular momentum (OAM) of photons and the corresponding mutually unbiased basis of angular position (ANG). Our experiment uses a digital micro-mirror device for the rapid generation of OAM and ANG modes at 4 kHz, and a mode sorter capable of sorting single photons based on their OAM and ANG content with a separation efficiency of 93\%. Through the use of a 7-dimensional alphabet encoded in the OAM and ANG bases, we achieve a channel capacity of 2.05 bits per sifted photon. Our experiment shows that, in addition to having an increased information capacity, QKD systems based on spatial-mode encoding will be more tolerant to errors and thus more robust against eavesdropping attacks

Influence of atmospheric turbulence on states of light carrying orbital angular momentum

We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number

Electroplating of CdTe thin films from cadmium sulphate precursor and comparison of layers grown by 3-electrode and 2-electrode systems

Electrodeposition of CdTe thin films was carried out from the late 1970s using the cadmium sulphate precursor. The solar energy group at Sheffield Hallam University has carried out a comprehensive study of CdTe thin films electroplated using cadmium sulfate, cadmium nitrate and cadmium chloride precursors, in order to select the best electrolyte. Some of these results have been published elsewhere, and this manuscript presents the summary of the results obtained on CdTe layers grown from cadmium sulphate precursor. In addition, this research program has been exploring the ways of eliminating the reference electrode, since this is a possible source of detrimental impurities, such as K+ and Ag+ for CdS/CdTe solar cells. This paper compares the results obtained from CdTe layers grown by three-electrode (3E) and two-electrode (2E) systems for their material properties and performance in CdS/CdTe devices. Thin films were characterized using a wide range of analytical techniques for their structural, morphological, optical and electrical properties. These layers have also been used in device structures; glass/FTO/CdS/CdTe/Au and CdTe from both methods have produced solar cells to date with efficiencies in the region of 5%–13%. Comprehensive work carried out to date produced comparable and superior devices fabricated from materials grown using 2E system

Engine Oil Filter Test Stand

For the current test stand, the cleaning time is too long. There is no way to run different types of filters. These problems negates them from collecting more data to compare various filters in various sizes.</p

Processing of CdTe thin films by intense pulsed light in the presence of CdCl2

Intense pulsed light (IPL) treatment was used for rapid thermal processing of electroplated CdTe layers, with and without CdCl2. Electroplated CdTe layers consist of small grains showing highly preferential orientation along the (111) planes. IPL processing improves the crystallinity keeping the (111) preferred orientation until an energy input threshold is reached. IPL treatment beyond this point shows a sudden structural transition within the layer with a decrease in each of the orientations. The addition of a CdCl2 treatment prior to the IPL initiates a transition from the preferred (111) orientation to randomly oriented grains throughout the film. X-ray diffraction, scanning electron microscopy, and optical microscopy were used to study the structural and morphological changes of these films