In this paper we present a simple technique for approximating laser process parameters needed for laser processing of crystalline silicon solar cells. The calculation computes the changes of silicon material properties during the time of laser-material interaction. As the laser pulse energy modifies optical and thermal properties of silicon, the chronological segmentation illustrates the temperature rise within the irradiated volume and indicates the time needed for melting or evaporation. Depending on the desired material modification, commercially available laser sources are analyzed regarding their process suitability. Simulating the laser system performance reveals its theoretical output and determines its expected efficiency. Simulations in this paper correlate well to experimental data and are done for different fields of interest:
a) ablation rate during laser drilling for EWT cells, using IR wavelengths in the order of 1 μs b) depth and width of laser grooves as used for Laser Grooved Buried Contact cells (LGBC) or edge isolation, using wavelengths in the IR and VIS
c) process windows during selective laser doping with 532 nm using PSG as sole phosphorous source d) laser parameters needed for Laser-Fired Contacts (LFC).
We present a photovoltaic tandem system made of two stacked fluorescent collector plates and gallium-indium-arsenide
(GaInP), gallium-arsenide (GaAs) and silicon (Si) solar cells, utilizing the spectral selectivity of fluorescent conversion.
Fluorescent collectors use fluorescent dye molecules embedded in a dielectric material to collect solar radiation.
Incoming radiation is converted into radiation of lower energy, reduced by the Stokes shift energy ΔE. Total internal
reflection keeps part of the converted radiation inside the collectors and guides it to the edges of the collector plates,
where GaInP and GaAs solar cells are mounted. In order to make use of the spectral selectivity of each collector, the
band gap energies Eg of the solar cells at the edges match the energy of dye emission. Optical transmission, reflection
and photoluminescence measurements analyze the fluorescent collectors. A spectral transfer matrix formalism allows us
to calculate the emitted photon flux of each collector as a function of the absorption/emission properties of the dye and
the spectrum of incident radiation. By multiplying the transfer matrices tailored on each collector with the quantum
efficiencies of the solar cells, we obtain the particular quantum efficiencies of each collector-cell sub-system and the
overall quantum efficiency of the tandem system. The results show very good agreement in the shape of predicted and
measured quantum efficiency curves of the tandem system.
The thermodynamic limits of photovoltaic solar energy conversion by fluorescent collectors are examined theoretically and experimaentally. The maximum efficiency of a fluorescent collector corresponds to the Shockley-Queisser limit for a non-concentrating solar cell with a single band gap energy. To achieve this efficiency the collector requires a photonic structure at its surface that acts as an omni-directional spectral band stop filter. Such a band stop filter is also required to achieve the thermodynamic light concentration limit in a fluorescent collector. The potential of photonic structures for the efficiency enhancement of idealized and real fluorescent collectors is highlighted. Analysis of a fluorescent collector system ny spatially resolved light induced current measurements and by quantum efficiency analysis shows that the collection efficiency of a real fluorescent collector system increases by up to 30% with the help of a Bragg stack on top of the collector acting as a band stop filter.