Monolithic two-terminal
(2T) perovskite/CuInSe
2
(CIS)
tandem solar cells (TSCs) combine the promise of an efficient tandem
photovoltaic (PV) technology with the simplicity of an all-thin-film
device architecture that is compatible with flexible and lightweight
PV. In this work, we present the first-ever 2T perovskite/CIS TSC
with a power conversion efficiency (PCE) approaching 25% (23.5% certified,
area 0.5 cm
2
). The relatively planar surface profile and
narrow band gap (∼1.03 eV) of our CIS bottom cell allow us
to exploit the optoelectronic properties and photostability of a low-Br-containing
perovskite top cell as revealed by advanced characterization techniques.
Current matching was attained by proper tuning of the thickness and
bandgap of the perovskite, along with the optimization of an antireflective
coating for improved light in-coupling. Our study sets the baseline
for fabricating efficient perovskite/CIS TSCs, paving the way for
future developments that might push the efficiencies to over 30%.