Nonconfinement Structure Revealed in Dion–Jacobson Type Quasi‐2D Perovskite Expedites Interlayer Charge Transport

Abstract

n-layered corner-sharing [BX 6 ] 4− octahedra separated by L, where n denotes the theoretical thickness of perovskite phase. [5] The L cation acts to improve both self-assembly capability and hydrophobicity of perovskite materials. [6,7] However, the poor interlayer charge carrier transport of 2D RP halide perovskites, which is attributed to the thick double insulating L layers, remains an open issue and invokes intense investigation.In general, the photogenerated excitons in 2D perovskites likely fall between the Wannier and Frenkel regimes where the exciton binding energy (E b ) depends not only on the number of inorganic layers (n), but also the organic spacer cations, offering the dielectric contrast against the inorganic layers. [8] Still, the dissociated charge carriers encounter the challenge of interlayer carrier transportation through the long-chain spacing cation layers. [9,10] In order to achieve more efficient exciton dissociation and interphase charge transport, Dion-Jacobson (DJ) type 2D perovskites, where the linker molecules bear two active sites have recently attracted increasing attention because only one spacing cation layer (L) is needed in-between the neighboring inorganic QWs. In an initial work, Karunadasa et al. reported the use of 2,2-(ethylenedioxy)bis(ethylammonium) as an organic spacer in 2D DJ perovskites to control the lattice distortion and the intrinsic trap states in thin film by forming an ionic bond between the NH 3 + and [PbX 6 ] 4− units. [11] In another early study, Zhao and co-workers included NH 2 C 4 H 9 COOH (Ava) with two different sites of NH 2 and COOH into MAPbBr 3 perovskite, disclosing another bonding of PbCOO − between Ava spacer and [PbX 6 ] 4− unit. [12] The above-mentioned two active sites result in the closer I···I interlayer distances and hence an enhancement of interface connection compared to RP type 2D perovskites. [13] Subsequently, numerous efforts have been made on a rational design of L cation based on either aliphatic [13][14][15][16][17][18][19][20][21][22] or aromatic [23,24] units to promote charge transport across the octahedra layers. In the former case, the linear chain with a variety of carbon chain lengths [13,14,22] and the annular chain with different locations of active site on aliphatic ring [17,21] gave rise to the highest power conversion efficiency (PCE) of 17.91% (n = 5) [14] and 12.04% (n = 4), [17] respectively. In the latter respect, Grätzel and co-workers more recently showed that a symmetric conjugated 1,4-phenylenedimethanammonium (PDMA) contain ing a conjugated benzene ring and two NH 3 + sites was introduced as L cation, which shortened the interlayer distance and enhanced π-π stacking relative to their RP counterpart, Dion-Jacobson (DJ) type 2D perovskites with a single organic cation layer exhibit a narrower distance between two adjacent inorganic layers compared to the corresponding Ruddlesden-Popper perovskites, which facilitates interlayer charge transport. However, the internal crystal structures in 2D DJ perovskites ...

Suppressing the Excessive Solvated Phase for Dion–Jacobson Perovskites with Improved Crystallinity and Vertical Orientation

“…[ 49 ] Here our results indicate that ion migration can still be efficiently suppressed in DJ perovskites, despite the much shorter interlayer spacing in PPD‐based DJ perovskite (4.66 Å) [ 50 ] (see Supporting Information, Figure S11 and Note 2) and PXD‐based DJ perovskite (6.74 Å). [ 51 ] On the other hand, this result also indicates an ignorable contribution to ion conductivity by the possible MAPbI 3 phase. The negligible hysteresis in J–V curves between reverse and forward scan (Figure 3b) also support the ignorable trends of ion migration in the DJ PSCs.…”

Structurally Tunable Two-Dimensional Layered Perovskites: From Confinement and Enhanced Charge Transport to Prolonged Hot Carrier Cooling Dynamics

“… 69 Consequently, the nonconfinement structure displayed E b of ∼69 meV which expedite exciton dissociation and interlayer charge transport. 69 This is in agreement with recent DFT calculation on ethylenediamine cation (EDE)-based 2D DJ perovskites, whereby n ≥ 3 samples offered enhanced stability, smaller effective masses, larger dielectric constants, and lower E b in comparison to their conventional 3D counterpart. 73 In fact, E b of (EDA)Cs n –1 Pb n I 3 n +1 perovskites ( n ≥ 3) falls between 29 and 46 meV, and their enhanced stability is related to the strong I–H interaction of diamine cations with a shortened interlayer distance of ∼3.5 Å.…”

Layered Perovskites in Solar Cells: Structure, Optoelectronic Properties, and Device Design

“…[35,246] An even smaller interlayer distance of 3.36 Å is obtained for the for n > 3 LPKs based on PDMA. [57] Hall effect measurements show p-type behavior with a carrier concentration of 3.00 × 10 8 cm -3 and Hall mobility of 0.75 cm 2 V -1 s -1 for n = 10, comparable to 3D perovskites. [247] The determined electron diffusion length of 800 nm, using intensitymodulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy, is again very similar to the 3D counterpart.…”

“…[60,61] For example, the small DJ-spacer p-xylylenediamine (PDMA) was shown to lead to non-confined structures at n > 3 with an interlayer distance of only 3.4 Å (Figure 4a). [57] This results in a reduced bandgap below 1.7 eV and lowered exciton binding energy down to 69 meV corresponding to a free charge carrier to exciton ratio of 97.9% under operating photovoltaic conditions. However, at larger d-spacings above 20 Å, systematic experimental and theoretical studies on aliphatic spacers have found the bandgap (2.7 eV) and exciton binding energy (320 meV) to be mostly independent of interlayer distance.…”