Experimental analysis of open-circuit voltage drop in quantum-dot solar cells via absolute electroluminescence measurement

Via absolute electroluminescence imaging measurement, we systematically examine the drops in open-circuit voltage (V
_OC
) and conversion efficiency for an InAs quantum dot (QD) solar cell, in contrast to a similar geometric GaAs bulk solar cell. Our results quantitatively reveal that apart from an extrinsic (V
_OC
) drop of 137mV stemming from the inferior lattice quality, an intrinsic drop of 115mV also co-exist in QD cell caused by the practical band edge extending towards lower energy. Moreover, the extrinsic and intrinsic drops in conversion efficiency are respectively evaluated as 5.6% and 1.6%, indicating even without lattice deterioration, such QD cell still cannot exceed the conversion efficiency of the bulk-host-material solar cell, if the boost in photocurrent cannot compensate the large intrinsic voltage drop induced by the narrow-gap QD material. This study could contribute to clarify the empirical characteristics of realistic QD solar cells, and also to verify the validity of the present theoretical QD-cell models.