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(C) In a solar cell,when light with energy $hf > E_g$ falls on the $p-n$ junction,electron-hole pairs are generated. These charge carriers are separat

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(C) In a solar cell,when light with energy $hf > E_g$ falls on the $p-n$ junction,electron-hole pairs are generated. These charge carriers are separated by the junction electric field,with electrons moving to the $n$-side and holes moving to the $p$-side.If no load is connected,these charges accumulate on the $n$ and $p$ sides,creating a photo-voltage.When an external load is connected,a photo-current $I_L$ flows through the circuit. In this state,the device acts as a power source,delivering power to the external load. The $V-I$ characteristic curve for this operation lies in the fourth quadrant,where the voltage $V$ is positive and the current $I$ is negative (indicating current flowing out of the device). Therefore,the diode generates power in the fourth quadrant.

When light shines on a $p-n$ junction diode,the current $I$ versus voltage $V$ is observed as in the figure below. In which quadrant$(s)$ does the diode generate power,so that it can be used as a solar cell?

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