Hii ,i don't understand one thing,normally if the temperature increases ,the voltage decreases !!
As temperature will increase the no. of generated carriers will further increase and the sweeping of these carriers,e- to n side and h to p side, will make the n side more -ve and the p side more positive resulting in higher Voc.
Sorry for the wrong answer before.
What you have stated is correct and the same holds true here too, as the temperature increases the Voc decrease (see effect of temperature).
The problem here with the calculator is that it doesn't account for the increase in Io with increase in temperature.
As temperature increases the Voc should rise according to the formula but the increase in Io due to the increase in temperature more than counters balances this rise and the net effect is decrease in Voc with increase in temperature.
Fundamentally too if we go then more the Band Gap more is the extractable voltage (Voc) and as the temperature increases the Band Gap decreases and hence the Voc should also reduce.