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.