1. PN junction as a solar cell. Consider a solar cell based on the PN junction. The current-voltage characteristics is defined by the standard equation as shown below: 1 = 1. (exp(e ) - 11, where the symbols have their usual meaning. The current direction is positive when it flows from P to N within the device. (a) Light with energy greater than the bandgap of the semiconductor shines on the PN junction. The current can now be expressed as: 1 = 1, [exp (ek) - 1] +BG where G is the light intensity. What is the sign of B? Explain with the help of an energy diagram of the PN junction. (b) Operating as a solar cell, show that at sufficiently high solar intensity under open-circuit conditions (i = 0), (c) The above equation shows that the output voltage increases with light intensity. There must be a limit to the magnitude of the output voltage from a solar cell. Discuss what this limit is.