Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laser-based fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemente

1 cm2 CH3NH3PbI3 mesoporous solar cells with 17.8% steady-state efficiency by tailoring front FTO electrodes

In this article, we investigate the effects of atmospheric-pressure chemical vapour deposited fluorine doped tin oxide (FTO) thin films as front electrodes for the fabrication of mesoporous perovskite solar cells with an active area of 1 cm2 and compare them with the use of a commonly used commercial transparent conducting oxide. The effects of sheet resistance (Rs) and surface roughness are both closely linked to the film thickness. In order to separate out these effects the characteristics of the deposited FTOs were carefully controlled by changing the fluorine doping levels and the number of passes under the coating head to give films of specific thicknesses or Rs. Under AM 1.5 Sun illumination and maximum power point tracking, the optimised FTOs yielded a steady-state power conversion efficiency of 17.8%, higher than that of the reference cell fabricated from the commercial FTO. We attribute the improved cell efficiency to increased fill factor and a lower series resistance resulting from the lower Rs and increased thickness of these FTO substrates. This low-cost and viable methodology is the first such type of study looking independently at the significance of FTO roughness and resistance for highly efficient mesoporous perovskite solar cells

Demonstrating the high Voc potential of PEDOT:PSS/c-Si heterojunctions on solar cells

In this study, we demonstrate the high surface passivation quality of PEDOT:PSS/c-Si junctions for the first time on solar cell level, reaching a record high Voc value of 688 mV after full-area metallization of the PEDOT:PSS. We achieve this by combining the PEDOT:PSS hole-selective layer at the rear of the crystalline silicon wafer with a well-passivating electron-selective a-Si:H(i/n) layer stack at the front. Our results clearly prove the excellent hole selectivity of PEDOT:PSS on crystalline silicon. © 2017 The Authors. Published by Elsevier Ltd

Limit of light coupling strength in solar cells

We introduce a limit for the strength of coupling light into the modes of solar cells. This limit depends on both a cell's thickness and its modal properties. For a cell with refractive index n and thickness d, we obtain a maximal coupling rate of 2c*sqrt(n^2-1)/d where c is speed of light. Our method can be used in the design of solar cells and in calculating their efficiency limits; besides, it can be applied to a broad variety of resonant phenomena and devices

Infrared laser-based monitoring of the silane dissociation during deposition of silicon thin films

The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions

Rapid actin monomer–insensitive depolymerization of Listeria actin comet tails by cofilin, coronin, and Aip1

Actin filaments in cells depolymerize rapidly despite the presence of high concentrations of polymerizable G actin. Cofilin is recognized as a key regulator that promotes actin depolymerization. In this study, we show that although pure cofilin can disassemble Listeria monocytogenes actin comet tails, it cannot efficiently disassemble comet tails in the presence of polymerizable actin. Thymus extracts also rapidly disassemble comet tails, and this reaction is more efficient than pure cofilin when normalized to cofilin concentration. By biochemical fractionation, we identify Aip1 and coronin as two proteins present in thymus extract that facilitate the cofilin-mediated disassembly of Listeria comet tails. Together, coronin and Aip1 lower the amount of cofilin required to disassemble the comet tail and permit even low concentrations of cofilin to depolymerize actin in the presence of polymerizable G actin. The cooperative activities of cofilin, coronin, and Aip1 should provide a biochemical basis for understanding how actin filaments can grow in some places in the cell while shrinking in others

Environmental proteomics reveals taxonomic and functional changes in an enriched aquatic ecosystem

Aquatic ecosystem enrichment can lead to distinct and irreversible changes to undesirable states. Understanding changes in active microbial community function and composition following organic matter loading in enriched ecosystems can help identify biomarkers of such state changes. In a field experiment, we enriched replicate aquatic ecosystems in the pitchers of the northern pitcher plant, Sarracenia purpurea. Shotgun metaproteomics using a custom metagenomic database identified proteins, molecular pathways, and contributing microbial taxa that differentiated control ecosystems from those that were enriched. The number of microbial taxa contributing to protein expression was comparable between treatments; however, taxonomic evenness was higher in controls. Functionally active bacterial composition differed significantly among treatments and was more divergent in control pitchers than in enriched pitchers. Aerobic and facultative anaerobic bacteria contributed most to identified proteins in control and enriched ecosystems, respectively. The molecular pathways and contributing taxa in enriched pitcher ecosystems were similar to those found in larger enriched aquatic ecosystems and are consistent with microbial processes occurring at the base of detrital food webs. Detectable differences between protein profiles of enriched and control ecosystems suggest that a time series of environmental proteomics data may identify protein biomarkers of impending state changes to enriched states