# Quantum Efficiency Mapping setup for solar cell charatcerization

1. Jun 5, 2009

### 2lai

In order to build a QE measurement system, I want to confirm the following issues: (1) Is collimated light required for QE characterization of the entire solar cell? How "bad" it could be if having Gaussian beam? (2) It seems LBIC is most common for QE mapping. Is it possible to use monochromatic light instead of laser for QE mapping? I guess the restrictions may include (a) light intensity; (b) wavelength drifting of monochromator in the long mapping duration (Yes or No?) (c) the series resistance of the grid may affect photo-current since photo-generated carriers at different location will travel different distance prior to collection (is this effect negligible?)

2. Jun 6, 2009

### Redbelly98

Staff Emeritus
Welcome to PF, I'll answer what I can.

(1)
Yes, you'd want a reasonably collimated beam, since the reflectivity of silicon will vary with angle of incidence. Collimated to within a few milliradians should definitely work, and probably within 5 degrees would work too.

Not sure why you think a Gaussian beam would be bad ... as long as it's reasonably collimated, it shouldn't matter if it's Gaussian or not.

(2)
Not sure what you mean, since a laser beam is monochromatic. Or do you mean you want to vary the wavelength? I'm not sure how much power you can get by using a monochromator as a filter on a white-light source.

3. Jun 7, 2009

### Bob S

Do you want to do this with sunlight, or with monochromatic light? The quantum efficiency varies with frequency, and is probably very poor in both the infra red and ultra violet regions. For "clean systems" like photomultipliers, QE measurement is relatively easy. For solar cells, measuring the output current is the only way to get QE, and dark current may interfere. What method do you plan to use for calibrating your light source, and how accurate a measurement do you need? How big a solar cell do you plan to use it on, and how fast do do want to do it (i.e., production line application)?

4. Jun 7, 2009

### 2lai

We plan to order a Class-B light source. The cell size is around 3x3 cm^2. The measurement system will be setup in 1-2 months.

5. Jun 7, 2009

### 2lai

Thanks Redbelly98.
(1) I should say focused beam rather than Gaussian beam. The intensity is not uniform (not collimated either) which may affect the measurement especially for large area cell.
(2) Adding a laser beam in the measurement system also add the complexity and \$. It is also my concern the output power of monochromatic light.