  Perovskite (CH3NH3PbI3) solar cells have made significant advances recently.
In this paper, we propose a bilayer heterojunction solar cell comprised of a
perovskite layer combining with a IV-VI group semiconductor layer, which can
give a conversion efficiency even higher than the conventional perovskite solar
cell. Such a scheme uses a property that the semiconductor layer with a direct
band gap can be better in absorption of long wavelength light and is
complementary to the perovskite layer. We studied the semiconducting layers
such as GeSe, SnSe, GeS, and SnS, respectively, and found that GeSe is the
best, where the optical absorption efficiency in the perovskite/GeSe solar cell
is dramatically increased. It turns out that the short circuit current density
is enhanced 100% and the power conversion efficiency is promoted 42.7% (to a
high value of 23.77%) larger than that in a solar cell with only single
perovskite layer. The power conversion efficiency can be further promoted so
long as the fill factor and open-circuit voltage are improved. This strategy
opens a new way on developing the solar cells with high performance and
practical applications.
