Bandgap Engineered Double-Cation/Double-Halide Quasi-Cubic Perovskite for Highly Efficient (>36%) Indoor Photovoltaics

Double-cation- and double-halide-based perovskites are well known for their better structural stability and improved efficiency in photovoltaics compared to single-cation-based perovskites. Herein, we have investigated the effects of the addition of formamidinium bromide (FABr) in methylammonium lead iodide (MAPbI
₃
) perovskite for the formation of a double-cation/double-halide (DCDH) perovskite structure, namely, MA
_1−
x
FA
_x
PbI
_3−
x
Br
_x
, which is specifically engineered for efficient indoor light harvesting. The indoor photovoltaics (IPVs) fabricated from the DCDH perovskite layer exhibited a distinctively higher short-circuit current density (
J
_SC
) of 172.64
μ
A·cm
⁻²
, an open-circuit voltage (
V
_OC
) of 0.91 V, and a power conversion efficiency (PCE) of 36.29% compared to the
J
_SC
of 159.03
μ
A·cm
⁻²
,
V
_OC
of 0.84 V, and PCE of 27.89% observed for the MAPbI
₃
IPVs under the simulated indoor LED light at 1000 lux. The use of formamidinium (FA
⁺
) cation and bromide (Br
⁻
) anion in the DCDH perovskite helps in stabilizing the perovskite crystalline phase from tetragonal to quasi-cubic, increases the bandgap, and complements the optical absorption in the visible region. Moreover, FA
⁺
and Br
⁻
suppress the trap states and nonradiative recombination loss in the DCDH perovskite structure. The results from this study will help researchers understand the mechanism of DCDH-perovskite-based IPVs, which is well explained by studying the charge carrier recombination dynamics and its correlation with the crystal structure of the perovskites under indoor lighting conditions. In addition, the optimized FABr-incorporated device exhibits a PCE of 20.59% under standard 1-sun conditions, which is better than the reference MAPbI
₃
device (17.16%).