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Author: Ahmed, K. ×

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  • Publication
    Laser Assisted Separation Processes for Bifacial pSPEER Shingle Solar Cells
    ( 2020)
    Münzer, Anna
    ;
    Baliozan, Puzant
    ;
    Ahmed, K.
    ;
    Nair, A.
    ;
    Lohmüller, Elmar orcid-logo
    ;
    Fellmeth, Tobias
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    Spribille, Alma
    ;
    Preu, Ralf
    In this paper, two laser-assisted separation processes (i) laser scribe and mechanical cleaving (LSMC) and (ii) thermal laser separation (TLS) for the separation of p-type silicon shingled passivated edge, emitter and rear (pSPEER) solar cells are examined. Both separation processes involve two process steps, where one of them is considered the main laser process that is conducted along the whole separation path (laser scribe for LSMC and laser cleave for TLS). We analyze the influence of the main laser process as well as the complete separation process of both, LSMC and TLS, on the electrical performance of pSPEER solar cells. We include an investigation of the dependency on the separation side, i.e. emitter (front side) or emitter-free side (rear side). It is found that by conducting the LSMC process from the front side, a significantly lower energy conversion efficiency by = -1.9%abs in comparison to the rear side process is observed which originates in particular from a lower pseudo fill factor pFF = -7.5%abs. This is attributed to local ablation of the p-n-junction leading to increased j02-like recombination. By conducting the laser scribe without subsequent mechanical cleaving of host cells, we measure pFF = -9.1%abs in comparison to the initial host cell measurement. This indicates that the laser ablation process itself leads to the strong pFF and losses observed after LSMC separation of pSPEER cells. In comparison, the TLS process is found to be invariant to the processed cell side. It is shown that in this case, the involved laser cleave process itself has no measurable impact on the performance of unseparated host cells.
  • Publication
    Control of slow axis mode behaviour with waveguide phase structures in semiconductor broad-area lasers
    ( 2011)
    Eckstein, H.-C.
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    Zeitner, U.D.
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    Ahmed, K.
    ;
    Schmid, W.
    ;
    Strauss, U.
    One of the most common methods to increase the output power of semiconductor waveguide lasers is broadening the stripe width of the active region. However, this results in higher order transverse modes to be amplified which impairs the beam quality and increases the beam divergence. By integrating optical elements into the cavity, it is possible to control the amplitude shape and the number of modes which are amplified in the laser. This paper reports on aspects to integrate phase and amplitude modifying microstructures into a semiconductor waveguide resonator by adding an additional lithographic step to the fabrication process of broad area laser diodes. The latest experimental results of such structured InGaAIP broad area lasers revealed a significant improvement of the beam quality even at a high operation current. Hence, the expansion of the stripe width of the amplifying region without degrading the beam quality is possible. The demonstrated power-current characteristics of structured laser diodes exhibit a low threshold current and a high efficiency.