DILIP
Last Activity: 8 Years ago
Basically, as you increase the temperature, the intrinsic carrier concentration increases. This pushes the fermi level closer to the intrinsic fermi level (the middle of the band gap). Since the built-in potential of a diode is determined by the difference in fermi-levels in the p-type and n-type regions, the fermi level in each region moves closer to the middle of the gap, and the built-on potential is decreased.
This is also a major contributor to why the performance of solar cells decreases at high temperatures. The operating voltage of a solar cell is related to the diode's built-in potential. As a solar cell gets hot, the voltage is reduced, and therefore the power output is reduced.
Another effect that can be considered: as the temperature of any semiconductor is increased, its band gap is reduced. This means that a solar cell will produce slightly more current. However, this is not enough to compensate for the decrease in voltage.