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

Abstract

This paper presents a quick methodology for focusing a laser beam on a photoactive surface based on performing a single line scan while simultaneously modifying the laser's position over the surface and the distance between the focusing lens and the active surface. The methodology was tested using the computer simulation technique. Several configurations were computer simulated by programming different experimental situations to discover the situations in which this focusing methodology would provide optimum results. The conclusions obtained from computer simulation methodology were checked by means of experimental tests using several solar cells, such as a thin-film amorphous silicon solar cell, a monocrystalline silicon solar cell, and a polycrystalline silicon solar cell. From the tests performed, we concluded that optimum focusing is achieved in systems in which the laser beam induced current signal generated by the photoactive surface has no large heterogeneities (e.g., fingers or grain boundaries), artefacts, or defects. Thus, the best results are achieved in systems where the surface of the photovoltaic device has a certain degree of homogeneity.

Scanning Light Stimulation System With Active Focus Correction at <inline-formula> <tex-math notation="LaTeX">$\mu \hbox{m}$</tex-math> </inline-formula> Resolution for PV Applications

“…With the exception of one method [11], these provide no compensation for geometrical surface changes (e.g., a bent or tilted surface) during the measurement, as the focus adjustment is fixed and done prior to the scan. The approach published by Navas et al uses a computer simulation to adapt the focus during the measurement [11]. Optimal focus conditions are found by analyzing simulated optical beam-induced current (OBIC) line scans, obtained for different distances between the sample and the focusing objective, in combination with an experimental verification.…”

“…To ensure that the LS beam diameter is minimal in the area under investigation, different focusing methods have been published [4]- [11]. With the exception of one method [11], these provide no compensation for geometrical surface changes (e.g., a bent or tilted surface) during the measurement, as the focus adjustment is fixed and done prior to the scan. The approach published by Navas et al uses a computer simulation to adapt the focus during the measurement [11].…”

“…A higher resolution allows a better structural analysis of sample properties, e.g., grain boundaries in multicrystalline solar cells [2] or while evaluating the emitter layer process homogeneity [3]. To ensure that the LS beam diameter is minimal in the area under investigation, different focusing methods have been published [4]- [11]. With the exception of one method [11], these provide no compensation for geometrical surface changes (e.g., a bent or tilted surface) during the measurement, as the focus adjustment is fixed and done prior to the scan.…”