• Light hitting solar cell generates carriers
• Carriers are swept through depletion zone by the built-in voltage, resulting in photocurrent I_L in the reverse bias direction
• Photocurrent generates voltage drop (V) across resistor
• This forward biases the pn junction, resulting in forward bias current I_F

Sources of Shunt Resistance (R_sh or R_shunt)
• Leakage around junction edges
• Leakage through defects or impurity phases

Sources of Series Resistance (R_s or R_series)
• Resistance in the semiconductor
• Resistance in the metal lines
• Contact resistance between conductor and semiconductor

Sources of Junction Non-ideality (1 ≤ m ≤ 2)
• Recombination of carriers in depleted region