After more than 20 years of research on rear side gratings for light trapping in solar cells, we have been able to demonstrate enhanced efficiencies for crystalline silicon solar cells with two different grating concepts and solar cell architectures. In both cases planar front sides have been used. With hexagonal sphere gratings and the tunnel oxide passivated contact (TOPCon) concept, a grating induced Jsc increase of 1.4 mA/cm2 and an efficiency increase of 0.8%absolute could be achieved. With binary crossed gratings fabricated by a nanoimprint based process chain, a grating induced Jsc gain of 1.2 mA/cm2 and an efficiency gain of 0.7% absolute could be achieved. For the binary grating concept, cell thickness variations have also been performed. The increasing importance of the light trapping properties towards low solar cell thicknesses could be confirmed by an enhanced EQE in the long wavelength region (Jsc increase: 1.6 mA/cm2 for 150 μm and 1.8 mA/cm2 for 100 μm thick solar cells). The results are in very good agreement with simulations using the OPTOS modeling formalism. OPTOS enables the further analysis and optimization of grating concepts in silicon solar cells and modules. So a grating induced Jsc gain of 0.8 mA/cm2 is forecast for solar cells with pyramidal front side texture. On module level, still a grating induced Jsc gain of 0.6 mA/cm2 can be expected.
Nanomaterials have the potential to revolutionize photovoltaics with the promise of new physics, novel architectures
and low cost synthesis. Silicon quantum dots, relative to their II-VI counterparts, are understudied
due to the difficulty of solution synthesis and chemical passivation. However, silicon is still an attractive solar
cell material, providing an optimal band gap, low toxicity, and a very solid body of physical understanding of
bulk silicon to draw from. We have synthesized silicon quantum dots with plasma enhanced chemical vapor
deposition, and have developed a method for chemical passivation of these silicon quantum dots that can be
used on particles created in a variety of ways. This versatile method utilizes oxidation via wet chemical etch and
subsequent siloxane bond formation. The attachment of a silane to the SiOx shell leads to stability of the silicon
core for over a month in air, and individual particles can be seen with TEM; thus a stable, colloidal suspension
is formed. The future for this technique, including increasing quantum yield of the particles by changing the
nature of the oxide, will be discussed.
Wavelength beam combining was used to co-propagate beams from 28 elements in a linear array of distributedfeedback
quantum cascade lasers (DFB-QCLs). The overlap of the beams in the far-field is improved using
wavelength beam combining; the beam-quality product of the array, defined as the product of near-field spot
size and far-field divergence for the entire array, was improved by a factor of 21. We measured the absorption
spectrum of isopropanol at a distance of 6 m from the laser arrays, demonstrating the efficacy of wavelength
beam combined DFB-QCL arrays for remote sensing.
The advent of continuous wave quantum cascade lasers operating at near room temperature has greatly expanded the
capability of spectroscopic detection of atmospheric trace gases using infrared absorption at wavelengths from 4 to 12
μm. The high optical power, narrow line width, and high degree of single mode purity result in minimal fractional
absorptions of 5x10-6 Hz-1/2 detectable in direct absorption with path lengths up to 210 meters. The Allan plot minima
correspond to a fractional absorbance of 1x10-6 or a minimum absorption per unit path length 5x10-11 cm-1 in 50s. This
allows trace gas mixing ratio detection limits in the low part-per-trillion (1 ppt = 10-12) range for many trace gases of
atmospheric interest. We present ambient measurements of NO2 with detection precision of 10 ppt Hz-1/2. The detection
precision for the methane isotopologue 13CH4 is 25 ppt Hz-1/2 which allows direct measurements of ambient ratios of
13CH4/12CH4 with a precision of 0.5 in 100 s without pre-concentration. Projections are given for detection limits for
other gases including COS, HONO and HCHO as CWRT lasers become available at appropriate wavelengths.
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