EFFICIENCY IMPROVEMENTS OF BACK-CONTACT TYPE PHOTOVOLTAIC CELLS

EFFICIENCY IMPROVEMENTS OF BACK-CONTACT TYPE PHOTOVOLTAIC CELLS


ABSTRACT: A back-contact type photovoltaic cell is able to simultaneously offer high light absorption and reduced resistance loss for high current densities. However, the structure requires low surface recombination velocities. A floating emitter was examined to reduce recombination loss at the surface of a Si substrate with a passivation layer.
The optimum specifications of the floating emitter were calculated using simulation analysis, and fabrication
utilized the thermal diffusion and ion implantation methods. The surface recombination velocities were estimated
by two-step effective lifetime measurements using the photo-conductance decay method. The velocity on the
emitter increased from 150 cm/s to 9,800 cm/s, but the efficiency improved from 17.7% to 19.3%. It was confirmed that the floating emitter serves as an energy barrier to prevent minority carriers from flowing to the surface defects.
Keywords: back contact, passivation, recombination

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