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.