Typical wavelength range for solar cell measurement
Silicon's band gap is about 1.1 eV, corresponding (by chance) to about 1.1 um wavelength. Therefore a silicon solar cell will have practically no response to longer wavelengths than 1.1 um, and it would be senseless to measure its response in that band.
The solar radiation reaching the earth drops dramatically below about 300 nm:




(source)

So measuring the solar cells response below 300 nm would not reflect its ability to extract power from sunlight.