Fluorination and Conjugation Engineering Synergistically Enhance the Optoelectronic Properties of Two-Dimensional Hybrid Organic–Inorganic Perovskites

Two-dimensional (2D) hybrid organic–inorganic
perovskites
(HOIPs) are expected to be a viable alternative to three-dimensional
(3D) analogs in solar cells (SCs) and optoelectronic devices due to
their high stability, diverse composition, and physical properties.
However, unsuitable band alignment and large bandgaps limit the power
conversion efficiency (PCE) improvement of SCs based on 2D HOIPs.
Here, we report a molecular design strategy that combines fluorination
and conjugation engineering to tune the electronic structure and optimize
the PCE of 2D HOIPs. Our results show that type IIa band
alignment and tunable bandgaps can be achieved in 2D Dion–Jacobson
(DJ) HOIPs by H/F substitution of organic cations with different degrees
of conjugation. In general, the bandgap of 2D DJ-HOIPs decreases monotonously
with the increase of the number of F atoms, which is due to the gradual
decrease of the lowest unoccupied molecular orbitals (LUMO) of organic
cations. In addition, the enhanced interlayer charge transfer and
higher dielectric constant suggest that the fluorination-induced dielectric
limitations are weakened. The estimated PCE of 2D DJ-HOIPs is exponentially
increased and positively correlated with the degree of conjugation
and fluorination of organic cations, with a PCE approaching 29% under
their synergistic effect. Our results not only provide promising candidates
for photovoltaic device applications but also provide an effective
method for PCE optimization.