A Breakthrough Efficiency of 19.9% Obtained in Inverted Perovskite Solar Cells by Using an Efficient Trap State Passivator Cu(thiourea)I

It is extremely significant
to study the trap state passivation
and minimize the trap states of perovskite to achieve high-performance
perovskite solar cells (PSCs). Here, we have first revealed and demonstrated
that a novel p-type conductor Cu­(thiourea)I [Cu­(Tu)­I] incorporated
in perovskite layer can effectively passivate the trap states of perovskite
via interacting with the under-coordinated metal cations and halide
anions at the perovskite crystal surface. The trap state energy level
of perovskite can be shallowed from 0.35–0.45 eV to 0.25–0.35
eV. In addition, the incorporated Cu­(Tu)I can participate in constructing
the p–i bulk heterojunctions with perovskite, leading to an
increase of the depletion width from 126 to 265 nm, which is advantageous
for accelerating hole transport and reducing charge carrier recombination.
For these two synergistic effects, Cu­(Tu)I can play a much better
role than that of the traditional p-type conductor CuI, probably due
to its identical valence band maximum with that of perovskite, which
enables to not only lower the trap state energy level to a greater
extent but also eliminate the potential wells for holes at the p–i
heterojunctions. After optimization, a breakthrough efficiency of
19.9% has been obtained in the inverted PSCs with Cu­(Tu)I as the trap
state passivator of perovskite.