Extended Sensitivity of a CCD Camera in the NIR (1150 nm) range.

As interest increases in the creation of alternate energy sources, solar cells are emerging as important components of an alternate energy production strategy.

During the fabrication process solar cells must be tested to identify defects. This is done by a combination of techniques including visual inspection as well as inspection of the device when placed under a power load.

In that case defects can be visualized as regions that emit light (electroluminescence) that encompasses higher VIS and near IR wavelengths.

Near Infra Red (NIR) inspection is a growing class of applications including:

ElectroLuminescence/PhotoLuminescence (EL/PL) imaging of crystalline photovoltaics

Other applications are numerous particularly in:

a) Life science imaging, e.g. viewing vascular structure
b) NIR fluorescence spectroscopy
c) Ophthalmic imaging

This document addresses only the EL/PL realm.

Most of these were previously addressable only by InGaAs and other expensive sensors. The use of a much less expensive CCD would benefit end users and OEMs by bringing the price of a system down dramatically.

The Sony ICX285AL Silicon CCD used in the DVC-1500M-QX camera has good QE response and an enhanced QE response in the NIR region of the spectrum.

NIR applications can benefit from this enhanced response in the 1500M-QX.

Panels A and B above are two images (taken with a DVC1500M-00-GE-QX) from a monocrystalline solar cell with current applied to induce electroluminescence, emitting at approximately 1000 nm. The black lines are the surface electrodes that run across the cell to collect the current. You can see the subtle decrease in emission between the electrodes, as expected. The cell is fractured on the left, resulting in the curved edge and reduction in intensity, which may be one of the cell failure modes of interest for manufacturers.

In this image the signal is relatively low. When the QX option was enabled, mean intensity values in the center of the cell went from 42 to 58, a 38% increase.

Both exposures were for 5 seconds with DVCView’s background subtraction feature applied to remove bright points. DVCView’s contrast stretching was also used to render the displayed images. Exposure (A) is with the QX option disabled, and exposure (B) is with QX enabled.

Panel (C) shows yet another image taken with the QX option enabled.

In Panel (D) one can see small defects in the cell disclosed by electroluminescence with the QX option of the DVC-1500M enabled.

In these additional applications images using the 1500M-QX camera the defects are obvious and clear.