Optimization Charge-Carrier Properties of 2D Ruddlesden–Popper Perovskite for Solar Cells

Two-dimensional
(2D) perovskites are tailored-photoelectric-responsive
materials owing to their lattice softness and designable multifunctional
spacer cations. However, the inferior charge-carrier characteristics
in these 2D systems are intolerable for photovoltaic devices. Here,
we introduced a novelty spacer cation 3,3-difluoropyrrolidinium (DFP)
to synthesize 2D Ruddlesden–Popper (RP) perovskite, (DFP)2PbI4. The multiple hydrogen bonds in the spacing
region of (DFP)2PbI4 drive the structure toward
uniqueness with the average PbIPb bond angles over
170°. This merit coupled with the large dipole moment of DFP
demonstrates the unique bandgap (2.20 eV) and small exciton binding
energies (99.76 meV) of (DFP)2PbI4. With the
stacking of inorganic layers, the (DFP)2MA4Pb5I16 (MA+: CH3NH3+) film demonstrated an improved electron diffusion length
(920 nm) and fast carrier extraction (0.73 μs) at the device
level. The resultant (DFP)2MA4Pb5I16 solar cells achieved a champion power conversion efficiency
(PCE) of 19.43%. Furthermore, the unencapsulated devices exhibited
excellent stability under continuous illumination and persistent heating
conditions.