If temperature is the only variable that is changed, then the efficiency of the solar cell decreases with increasing temperature.

Solar cells have three parameters that are used to determine their efficiency: short circuit current (Isc), open circuit voltage (Voc), and their fill factor. The efficiency is a product of these three parameters so we want large values for all three.

The Voc is affected most by temperature and decreases when it gets hotter so that we lose efficiency. The Voc is dependent on the band gap of a material or the minimum amount of energy needed for the material to absorb the light. Temperature decreases the band gap so the minimum energy needed for the material is lowered. This may seem like a good thing because it should absorb more light, but it's actually terrible for efficiency because energy in light that is larger than the band gap is lost as heat.

For instance, if the material has a band gap of 1.1eV, it will absorb all light that is 1.1eV or greater in energy. If the light is 1.1eV in energy, that's perfect because most of that energy is converted to electricity. So now if the temperature is increased, the band gap will decrease. Let's just say the band gap is now 1.0 eV. In this high temperature case, when the 1.1eV light is absorbed, only 1.0eV of the energy is used to generate electricity. The difference of 0.1 eV is lost as heat. The Isc is slightly increased when it gets hotter, but this is a minimal effect and can not compensate for the loss in Voc.

If you're interested in learning more about solar cells, here is a good resource.