= Solution
The longest wavelength capable of producing an above-gap <electron-hole pair> is
$$
\lambda_g=\frac{hc}{E_g}\simeq\frac{1240}{2.4}=517\,\mathrm{nm}.
$$
Every transmitted wavelength is longer than $600\,\mathrm{nm}$, so every transmitted photon has energy below $2.4\,\mathrm{eV}$. Consequently the ideal single-photon absorber generates no photocurrent and \b[$\boxed{\eta=0\%}$]. The stated irradiance does not change this spectral-threshold conclusion. Defect-mediated or multiphoton absorption is outside the assumed ideal band-to-band model.
Back to article page
