Voltage enhancement in quantum well solar cells


The power conversion efficiency of a conventional solar cell is constrained fundamentally by the competing benefits of a low band gap, which maximizes light absorption and output current, and a high band gap, which maximizes output voltage. The quantum well solar cell (QWSC) is a novel approach to higher efficiency. In its simplest form (the QWSC consists of a multiquantum well (MQW) system in the undoped region of a p - i - n cell. Long wavelength light can be absorbed in the wells. If the material quality is good, the  electrons  and  holes  escape  from  the  quantum  wells (QWs) with high efficiency in forward bias. We have dem- onstrated that the short circuit current (I sc) and efficiency of QWSCs can be enhanced over comparable, homogeneous (control) cells made from the barrier material. Under white light illumination the efficiency of a number of AlGaAs/ GaAs
MQW structures was more than double that of identi- cally grown control structures without the quantum wells.

Our measurements and modeling of the spectral re- sponse  of  a  range  of  AlGaAs/GaAs and  GaAs/InGaAs
QWSCs suggest that the enhancement of short-circuit current is well understood. However, the voltage dependence   of the QWSC has proved more difficult to quantify.








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