Zwitterion-Assisted Crystal Growth of 2D Perovskites with Unfavorable Phase Suppression for High-Performance Solar Cells

Abstract

Despite two-dimensional (2D) Ruddlesden–Popper-phase layered perovskites (RPLPs) exhibiting excellent environmental stability, most solar cells based on 2D RPLP films are fabricated in a controlled inert atmosphere. Meanwhile, the poor charge transport of 2D RPLP films owing to the unfavorable phase arrangement and defects limits the efficiency of 2D RPLP solar cells. Here, we fabricate high-efficiency 2D RPLP solar cells in ambient air assisted by a zwitterion (ZW) additive. We show that the ZW additive suppresses the formation of the bottom 2D phases (n ≤ 2) and the top 3D-like phases in 2D RPLP films. These 2D phases usually grow parallel to the substrate and act as trap sites that inhibit charge transport in the vertical direction. The 3D-like phases, on the other hand, aggravate the long-term stability due to the intrinsic instability of MA+ cations. With improved phase distribution, crystal orientation, and reduced trap states in 2D RPLP films, efficient charge transport is obtained. Finally, a record-high open-circuit voltage (V oc) of 1.19 V and a power conversion efficiency of 17.04% with an enhanced stability are achieved for (BA0.9PEA0.1)2MA3Pb4I13-based (n = 4) solar cells fabricated under high humidity (∼65% RH).

Suppressed Energy Transfer Loss of Dion–Jacobson Perovskite Enabled by DMSO Vapor Treatment for Efficient Sky-Blue Light-Emitting Diodes

“…The energy band gap of a quasi-2D phase is decreased with the increased layers ( n ) of lead bromide octahedra, and the energy of excited states cascades from the small- n phases to the large- n phases . Nevertheless, the strong electron–phonon coupling and inefficient energy transfer of the small- n phases would largely decrease the luminescence efficiencies of perovskite films. ,− More and more works thus are focused on this issue by the modulation of small- n phase distribution. , For instance, the addition of the 2D perovskite PEA 2 PbBr 4 is shown to effectively suppress the formation of small- n phases and significantly facilitate the energy transfer . In addition, the bidentate ligand 4-(2-aminoethyl)­benzoic acid was used to diminish the weak van der Waals gap between the quasi-2D phases of Ruddlesden–Popper (RP) perovskites, contributing to an efficient energy transfer and sky-blue light emission .…”

Ruddlesden–Popper Perovskites with Narrow Phase Distribution for Air‐Stable Solar Cells

“…The high degree of perpendicularly orientation and narrow phase distribution of the HC + APSA film has promising implications for device performance. [ 37,58 ]…”

“…The high degree of perpendicularly orientation and narrow phase distribution of the HC þ APSA film has promising implications for device performance. [37,58] Clearly, while both AS and HC films are free of parasitic n ≤ 2 and n ¼ ∞ phases, only HC films have benefitted from MACl additive to form perpendicularly oriented 2D-RPP crystallites. Indeed, the HC films without MACl additive exhibit weak scattering rings characteristic of mixed 2D-RPP phases with high-n value and n ¼ ∞ phases, with weak crystallinity and considerable randomness in the polycrystalline orientation (Figure S5a, Supporting Information).…”

High Efficiency Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

“…Overall, while the fabrication of 3D perovskites usually takes place in N 2 -filled gloveboxes to avoid the presence of water and oxygen, RPPs have shown potential with regards to being fabricated in ambient air, with important consequences for upscaling. [70,85,86]…”

“…This condition was successfully met when mixing two spacers, no matter their size or molecular shape, but efficiencies >14% were reached only with BA and PEA. More recently, a mixture of BA and PEA as organic spacers with the addition of a sulfobetaine zwitterionic additive has been successfully used to fabricate a solar cell with PCE of 17.04% [ 70 ] The addition of this SO containing additive has led to a more homogeneous phase distribution and an alleviated competition between MA and BA during the crystallization process because of its interaction with the perovskite precursors, proving that additive engineering to tune the colloidal properties of the precursor solution is a suitable strategy to improve solar cell performances. Liu et al mixed BAI with bulky 1‐naphthalenemethylammonium (NMA), showing the existence of a delicate equilibrium between enhanced interlayer interaction and vertical orientation, poor morphology, and formation of low‐ n phases.…”