New Type of 2D Perovskites with Alternating Cations in the Interlayer Space, (C(NH₂)₃)(CH₃NH₃)_nPb_nI_3n+1: Structure, Properties, and Photovoltaic Performance

Abstract

We present the new homologous series (C­(NH2)3)­(CH3NH3) n Pb n I3n+1 (n = 1, 2, 3) of layered 2D perovskites. Structural characterization by single-crystal X-ray diffraction reveals that these compounds adopt an unprecedented structure type, which is stabilized by the alternating ordering of the guanidinium and methylammonium cations in the interlayer space (ACI). Compared to the more common Ruddlesden–Popper (RP) 2D perovskites, the ACI perovskites have a different stacking motif and adopt a higher crystal symmetry. The higher symmetry of the ACI perovskites is expressed in their physical properties, which show a characteristic decrease of the bandgap with respect to their RP perovskite counterparts with the same perovskite layer thickness (n). The compounds show a monotonic decrease in the optical gap as n increases: E g = 2.27 eV for n = 1 to E g = 1.99 eV for n = 2 and E g = 1.73 eV for n = 3, which show slightly narrower gaps compared to the corresponding RP perovskites. First-principles theoretical electronic structure calculations confirm the experimental optical gap trends suggesting that the ACI perovskites are direct bandgap semiconductors with wide valence and conduction bandwidths. To assess the potential of the ACI perovskites toward solar cell applications, we studied the (C­(NH2)3)­(CH3NH3)3Pb3I10 (n = 3) compound. Compact thin films from the (C­(NH2)3)­(CH3NH3)3Pb3I10 compound with excellent surface coverage can be obtained from the antisolvent dripping method. Planar photovoltaic devices from optimized ACI perovskite films yield a power-conversion-efficiency of 7.26% with a high open-circuit voltage of ∼1 V and a striking fill factor of ∼80%.

Highly Efficient Guanidinium‐Based Quasi 2D Perovskite Solar Cells via a Two‐Step Post‐Treatment Process

“…Figure b shows the absorption spectra of 0–6 GASCN sample films. The exciton absorption peaks at about 580 and 620 nm are respectively attributed to n = 2 and n = 3 species, indicating the formation of 2D GAMA 4 Pb 4 I 13 which contains multiphase with different n value (see Figure S6, Supporting Information). The 0 GASCN film presented higher absorption intensity than the 2 GASCN film because of the existence of larger crystal gain in the 0 GASCN film (see Figure a,b).…”

“…In addition, a new type of 2D perovskites was introduced by Soe et al which employed two different alternating cations in the interlayer space (ACI) . This ACI type perovskite can be described by the formula of GAMA n Pb n I 3 n +1 or (GAMA)MA n −1 Pb n I 3 n +1 (GA = guanidinium, MA = methylammonium), where two different kinds of cations (GA + and MA + ) are combined in the interlayer space.…”

“…This ACI type perovskite can be described by the formula of GAMA n Pb n I 3 n +1 or (GAMA)MA n −1 Pb n I 3 n +1 (GA = guanidinium, MA = methylammonium), where two different kinds of cations (GA + and MA + ) are combined in the interlayer space. The ACI 2D perovskites exhibit narrower optical bandgaps, lower exciton binding energy, and longer carrier lifetime ascribed to the small volume of GA and MA, compared with typical RP 2D perovskites which have higher exciton binding energy and inefficient charge transfer due to the multiple quantum wells structure within the films …”

“…Despite these advantages of ACI perovskites, the film morphology control remains a challenge. An antisolvent method was applied to fabricate ACI quasi‐2D PVSCs, resulting in optimized devices with a PCE of 7.3% ( n = 3) . This type of perovskite solar cell was further developed through solvent engineering to fabricate a new type of quasi‐2D PVSCs, which obtained optimal PCE of 12.8% ( n = 4) and 14.7% ( n = 3), respectively .…”

Band‐Edge Exciton Fine Structure and Exciton Recombination Dynamics in Single Crystals of Layered Hybrid Perovskites

“…[6,7] Very recently, quasi-2D Ruddlesden-Popper perovskites, a family of layered compounds with tunable semiconductor characteristics, have also been explored for optoelectronic devices. [12,13] Furthermore, layered perovskites afford specific advantages over other inorganic 2D been intensively investigated, [28][29][30][31][32] the investigation of excitonexciton interactions, biexcitons, and their recombination dynamics remains modest. [12,13] Furthermore, layered perovskites afford specific advantages over other inorganic 2D been intensively investigated, [28][29][30][31][32] the investigation of excitonexciton interactions, biexcitons, and their recombination dynamics remains modest.…”