This document summarizes research on using supramolecular engineering to design formamidinium-based layered two-dimensional perovskite solar cells. A (adamantan-1-yl)methanammonium spacer was incorporated to provide structural stability through van der Waals interactions. Characterization using solid-state NMR spectroscopy revealed the atomic-level interactions between the spacer and inorganic layers. Devices based on the A2FA2Pb3I10 composition achieved a power conversion efficiency of 7.8% with long-term stability, representing a promising approach for improving perovskite solar cell performance and stability.

1. Supramolecular Engineering for Formamidinium
Based Layered Two-Dimensional
Perovskite Solar Cells:
Structural Complexity and Dynamics Revealed by
Solid State NMR Spectroscopy

2. Perovskite Solar Cells
• Perovskite is a type of solar cells that are three dimensionally hybrid of organic
(methylammonium lead halide) and inorganic (lead/tin halides) materials.
• PSC has light harvesting layer.
• High performance perovskite solar cells suffer from chemical instability.

3. Perovskite is a
crystalline structure
having unit formula
of ABX3.
Perovskite name is
based on Russian
minerologist L. A
Perovskite.
Perovskite

4. Ruddlesden-Popper phases (RPP)
Supramolecular engineering
of 2D perovskite materials
such as Ruddlesden-Popper
phases (RPP) have
demonstrated promising
environmental stability.

5. Supramolecular
Design
• 2D Ruddlesden-Popper (RPP) phases comprise of two
layers of interacting monovalent cations of organic spacer
between the 3D perovskite inorganic slabs. The overall
structure is determined to a great extent by the structural
features of the organic spacer and interaction with the
inorganic slabs, as well as the contacts between the
adjacent spacer units.
• (adamantan-1-yl) Methanammonium (A), which features
an adamantane core equipped with a –CH2NH3
+group into
the FA-based layered perovskite composition.

6. Supramolecular Approach
Our approach incorporates the adamantane core to provide a 2D backbone through Van der
Waals interactions within the hydrophobic spacer bilayer, which could enable higher
electronic quality of resulting material. The adamantane scaffold was functionalized with an
ammonium moiety to ensure interaction with the inorganic layers through hydrogen bonding.
Hydrogen bond donating group was linked through a flexible methylene unit that was
assumed to feature a higher level of adaptability to the geometrical mismatches in the overall
structure in order to achieve a more robust structural framework.

7. Concept of supramolecular engineering of 2D
perovskite materials in the case of formamidinium
(FA) containing A2FAn–1PbnI3n+1 formulations by
employing (adamantan-1-yl)methanammonium (A)
spacers exhibiting propensity for strong Van der
Waals interactions complemented by structural
adaptability.
The molecular design translates into
desirable structural features and phases with
different compositions and dimensionalities,
identified uniquely at the atomic level by
solid-state NMR spectroscopy. For
A2FA2Pb3I10 we achieve efficiencies
exceeding 7% in mesoscopic device
architectures without any additional
treatment or use of antisolvents for ambient
temperature film deposition.

8. Morphology
• The morphology of films based
on the A2FAn–1PbnI3n+1
composition was investigated by
scanning electron microscopy
(SEM).

9. Fig. 1 Plane view SEM images Fig. 2 Cross sectional SEM images

10. Optoelectronic
Properties
• The distinct feature of layered 2D perovskites is
that their optoelectronic properties are largely
determined by their quantum well behavior, which
leads to a gradual decrease in the optical band gap
(Eg) with an increase in the number of inorganic
layers from n = 1 (S2PbI4) to n = ∞ (α-FAPbI3).

11. • Optoelectronic properties in layered 2D-A perovskites are investigated
by means of UV-Vis absorption and photoluminescence (PL)
spectroscopy.

12. UV-VIS
Absorption
Spectra
• The corresponding UV-Vis
absorption spectra show strong
exciton absorption peaks and a
gradual red shift of the absorption
spectrum with an increase in the
number of layers (n), which is in
accordance with the formation of
a layered 2D structure (Figure 2a).

13. PL
Spectroscopy
• Time-resolved PL spectroscopy on mp-
TiO2/c-TiO2/FTO substrates confirms that
the potential edge state signals have longer
PL decay times as compared to the main
exciton emission (Figure 2e–f).
• Moreover, the PL decay times in the
perovskite films gradually increase with the
number of inorganic layers (Figure 2e) also
pointing to the increasing contribution of
the layered edge states.

14. Fig. 3 Optoelectronic properties of 2D-A Perovskites

15. Photovoltaic Performance
The structural and optoelectronic properties of 2D perovskite materials are of
interest for photovoltaic (PV) applications. As n > 2 compositions are known to
display a preference for perpendicular orientation with respect to the substrate.
They demonstrate the more effective charge-extraction efficiency, an important
aspect for photovoltaics.

16. • The highest-performing device based on A2FA2Pb3I10 composition gave a
short circuit current density (JSC) of 14.3 mA 𝑐𝑚−2, open circuit voltage
(VOC) of 1.08 V, and fill factor (FF) of 0.50, resulting in a PCE of 7.8% .
• This performance can be ascribed to the enhancement of the current
densities, as a result of better film quality based on Van der Waals
interactions and adaptability of the novel organic spacer to a more robust
layered structure.

17. Fig. 4 Photovoltaic performance of of 2D-A Perovskites

18. Structure
Characteristics
• The structure of A2FAn–1MnX3n+1 and A’2FAn–
1MnX3n+1 films was analyzed by means of XRD.
• Diffractograms of the perovskite films on
FTO/c-TiO2/mp-TiO2 and glass substrates show
low angle reflections below 10° typical for 2D
perovskite materials.

19. Fig. 5 Structural properties of 2D-A Perovskites by XRD

20. NMR
To elucidate the atomic-level
origin of the effects of spacer on
the properties of 2D layered
perovskite material, solid state
nuclear magnetic resonance
(NMR) spectroscopy
measurements were carried out.
To probe the atomic-level
interaction between spacers and
α-FAPbI3, carbon-13 (13C) and
nitrogen-15 (15N) magic angle
spinning (MAS) NMR spectra at
100 K was developed.

21. Fig. 6 C13
and H1
solid state magic angle spinning (MAS) NMR spectra of 2D-A Perovskites

22. • Based on the NMR analysis, we conclude
that both spacer cations, A and A’,
interact with the [PbI6]−4
sublattice,
which is a prerequisite for the formation
of layered 2D structures.
• In addition, regardless of the formal
stoichiometry of the precursors, a
mixture of phases is formed
accompanied by additional 3D phases in
the bulk for n ≥ 2 compositions,
indicative of the formation of mixed
2D/3D structures.

23. Long term stability
Degradation of the hybrid perovskite solar
cells is commonly associated with the
decomposition of the active perovskite layer
by exposure to environmental conditions, in
particular oxygen and moisture. Therefore,
long-term performance of 2D perovskite
solar cells probed by measuring the stability
under inert and humid ambient air
conditions. the hydrophobicity of the
perovskite films is an important factor in
Hydrophobicity of the perovskite films is an
important factor in achieving long-term
stability against detrimental environmental
factors.

24. • long-term stability was evaluated by
monitoring the maximum power
point (MPP) under full sun
illumination under inert conditions
at ambient temperature, showing
maintained >84% PCE over more
than 800 h of continuous operation.

25. Conclusions
The atomic-level interaction between the spacer and the
inorganic perovskite layers, as well as their static and
dynamic properties, are unraveled through UV-Vis, PL
spectroscopy, PV, XRD and solid state NMR spectroscopy.
This prototype enabled the achievement of efficiencies up
to 7.8% for FA-based two-dimensional perovskite solar
cells without any additional treatment or further
optimization, accompanied by long-term stability