Answer
1.1 eV
Work Step by Step
The longest-wavelength photon, in order to be absorbed, should have an energy equal to the gap energy. (If the gap energy were any larger, these photons wouldn’t be absorbed, and the solar cell would be less efficient.)
$$E_g=hf=\frac{hc}{\lambda}$$
$$=\frac{(6.63\times10^{-34}J \cdot s)(3.00\times10^8m/s)}{(1.60\times10^{-19}J/eV)(1100\times10^{-9}m)}$$
$$=1.1 eV$$