Abstract:
Energy conversion efficiency is a major issue for photovoltaic cells today. Researchers are
continuously trying to improve the efficiency level of photovoltaic devices by introducing
new materials and advanced concepts. The target is to reach a high efficiency level within
affordable cost, which will lead to a mass generation of electricity using photovoltaic devices.
In this work, a new structure of CdS/CdTe based solar cell is proposed, where two of the
fundamental drawbacks of traditional CdS/CdTe cell are addressed. The relatively low
bandgap of CdS window layer, along with a significant lattice mismatch between CdS and
CdTe decrease the efficiency of conventional CdS/CdTe solar cell. This work proposes a
novel structure where both window (CdS) and absorber (CdTe) layer are replaced by two IIVI
ternary alloys, namely, Cd1-xZnxS and Cd1-xZnxTe respectively. These alloys give
advantage of variable bandgap by varying Zn concentration in the alloys. A new structure of
TCO/ZnO/Cd1-xZnxS/Cd1-xZnxTe/Cu2Te/Ni is proposed, which can easily be achieved by
replacing S by Te during various fabrication processes. Numerical analysis was performed
with AMPS 1D software and an efficiency of 24.643% was achieved through bandgap
engineering, which is higher than the conventional CdS/CdTe solar cell. The solar cell was
also found to be stable at higher temperature.
A modified solar cell structure was proposed, consisting of TCO/ZnO/Cd1-xZnxS/Cd1-
xZnxTe/Cu2Te/Ni in which alloy composition was varied in the window layer for achieving a
better windowing effect that gives better Jsc. But it was accompanied by detrimental Voc and
FF, which were then improved by varying alloy composition in the absorber layer which
improved lattice matching. A small range of Zn x% around x = 0.2 was found, when the
proposed two-fold treatment eventually yielded a better efficiency of 24.643%. The lattice
mismatching of modified Cd0.8Zn0.2S /Cd0.8Zn0.2Te was found to be 10.16%, which resembles
the original CdS/CdTe lattice mismatch. However, this structure yielded better Jsc and Voc,
which ultimately resulted in a high efficiency solar cell. The cell also showed very good
temperature stability, giving an efficiency gradient of 0.05%/C0.This study shows that careful
modification of bandgaps of window and absorber layer can yield better efficiency
