High resolution laser beam induced current images under trichromatic laser radiation: Approximation to the solar irradiation

Abstract

A laser beam induced current (LBIC) map of a photoactive surface is a very useful tool when it is necessary to study the spatial variability of properties such as photoconverter efficiency or factors connected with the recombination of carriers. Obtaining high spatial resolution LBIC maps involves irradiating the photoactive surface with a photonic beam with Gaussian power distribution and with a low dispersion coefficient. Laser emission fulfils these characteristics, but against it is the fact that it is highly monochromatic and therefore has a spectral distribution different to solar emissions. This work presents an instrumental system and procedure to obtain high spatial resolution LBIC maps in conditions approximating solar irradiation. The methodology developed consists of a trichromatic irradiation system based on three sources of laser excitation with emission in the red, green, and blue zones of the electromagnetic spectrum. The relative irradiation powers are determined by either solar spectrum distribution or Planck's emission formula which provides information approximate to the behavior of the system if it were under solar irradiation. In turn, an algorithm and a procedure have been developed to be able to form images based on the scans performed by the three lasers, providing information about the photoconverter efficiency of photovoltaic devices under the irradiation conditions used. This system has been checked with three photosensitive devices based on three different technologies: a commercial silicon photodiode, a commercial photoresistor, and a dye-sensitized solar cell. These devices make it possible to check how the superficial quantum efficiency has areas dependent upon the excitation wavelength while it has been possible to measure global incident photon-to-current efficiency values approximating those that would be obtained under irradiation conditions with sunlight.

Experimental analysis and computer simulation of a methodology for laser focusing in the solar cell characterization by laser beam induced current

“…Laser wavelength (λ/μm) 0.6328 Lens focal length (D/μm) 15 700 Pre-focused Gaussian diameter of the laser beam (d/μm) 820 Laser Gaussian radius at x = 0, i. e., at focus (w 0 /μm) 7.71 Line scan step ( y, z/(μm)) 3.0 Scan range of the focal lens (x/μm) (x f ) optimal -500 Scan step of the focal lens ( x/μm) Figure 1, and it has already been described in the literature. 26,29 To check the goodness of the focusing made using the methodology proposed in this paper, we compare the results with the results obtained using a "classical" methodology reported by authors. 27 This classical methodology has been extensively checked, and it allows obtaining an optimum focusing with great precision.…”