Evaluation of Carrier Collection Efficiency in Multiple Quantum Well Solar Cells

The carrier collection efficiency (CCE) is proposed as an effective parameter for indicating the efficiency of carrier transport in quantum nanostructured solar cells. The CCE can be estimated by normalizing the illumination-induced current enhancement to its saturation value at reverse bias. The derivation procedure for the CCE is experimentally validated by examining the bias-dependence of light absorption, and by investigating the balance between the absorbed photons and collected carriers at reverse bias. The effect of AM1.5 bias-illumination for CCE characterization was also investigated and found to be significant for more accurate evaluation of carrier dynamics during actual device operation under sunlight. Furthermore, simulation of the resistance effects showed that a large series resistance leads to underestimation of the CCE at forward bias whereas a shunt resistance has only a slight influence on the CCE calculation.