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LBIC

Mikkel Jørgensen infinityPV desktop LBIC

Light Beam Induced Current (LBIC) (or Laser Beam Induced Current) works by scanning a small spot of light (usually from a laser) over the solar cell while measuring the current generated (see video). The current values at each point are translated to a color value and shown as a 2D map representing how well the solar cell works. Electrical defects can be easily visualized with this technique and it was therefore invented early on for silicon solar cells. This characterization technique is a very valuable tool complementing non-localized measurements of the IV-curve and the IPCE. It is one of the few methods for accurately measuring the active area which is an important parameter for calculating the power conversion efficiency (PCE). LBIC systems are commercially available (e.g. infinityPV.com)

Figure 1: Left: An OPV module that has been crumbled (by purpose). Right: the LBIC image showing that some areas actually remained working despite the harsh treatment.

The standard implementation of LBIC involves a 2D translation stage that moves the laser (or solar cell) and a source measure unit both connected to a computer to control them. DTU Energy Conversion have invented a new and greatly improved type of LBIC instrument using only seconds to measure solar cells up to 25x25 cmDOI:10.1016/j.solmat.2010.11.007. The scanning speed is improved using a motor controlled mirror to direct the laser beam and custom build electronics to measure the output of the solar cell.

Figure 2: Roll-to-roll LBIC characterization of OPV using a contactless mode showing how non-functional cells and defects can be identified.

A further refinement includes contactless measurement modes and signal processing. External electrodes are used that overlap (but does not touch) the larger positive and negative terminals of the solar cell module. This arrangement forms capacitive circuit elements that allow measurement of time dependent current and voltage fluctuations as a function of the light beam scanning. This mode of the LBIC technique makes it very suitable for roll-to-roll characterization of OPV. DOI:10.1002/adom.201400016

The LBIC measurement can also be used to accurately calculate the actual area of a solar cell. This area is highlighted in the LBIC image and can be measured directly by the pixels per centimeter ratio. Another possibility is to include a scale that is overlaid the solar during the measurement. This can be done using a millimeter grid printed on clear plastic or with a clear plastic ruler. The markings of the grid or ruler will shadow the solar cell and be recorded in the LBIC image, making the area calculation straight forward.

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