In this study, I investigated a synergistic interface engineering strategy for inverted perovskite solar cells using a heteroatom-rich crown ether derivative, 1-aza-12-crown-4 (A12C4). The rapidly advancing field of perovskite solar cells has reached certified efficiencies beyond 26%, yet the practical deployment of perovskite solar cells is still hindered by surface defects, interfacial energy level mismatch, and environmental instability. In inverted p-i-n perovskite solar cells, the top surface of the perovskite film is particularly vulnerable because it is exposed during subsequent electron transport layer deposition and device operation. Undercoordinated Pb²⁺ ions, halide vacancies, and residual PbI₂ phases introduce deep-level traps that act as non-radiative recombination centers, reducing the open-circuit voltage (\(V_{OC}\)) and fill factor (\(FF\)) of perovskite solar cells. Moreover, energy level misalignment between the perovskite absorber and the electron transport layer (ETL) creates an electron injection barrier, limiting charge extraction and overall power conversion efficiency (\(PCE\)). Therefore, I aimed to develop a molecular interface modifier that can simultaneously passivate surface defects and optimize interfacial energy level alignment in perovskite solar cells.
The molecule A12C4 possesses a cyclic backbone containing multiple ether oxygen atoms and one secondary amine nitrogen atom. These heteroatoms are Lewis basic and can donate lone pair electrons to coordinatively unsaturated Pb²⁺ sites. I hypothesized that A12C4 would form stable Lewis acid-base adducts with surface Pb²⁺, thereby reducing defect density and suppressing non-radiative recombination in perovskite solar cells. In addition, the coordination-induced surface charge redistribution and interfacial dipole formation could shift the surface Fermi level and optimize the energy level alignment between the perovskite and the ETL. This dual function is expected to enhance both the photovoltaic performance and the operational stability of perovskite solar cells. In the following sections, I describe the experimental methods, material characterizations, carrier dynamics, energy level regulation, device performance, and stability of A12C4-modified perovskite solar cells.
Experimental Methods and Device Fabrication
I fabricated inverted perovskite solar cells with the device architecture FTO/4PADCB/perovskite/A12C4/C60/BCP/Cu. The FTO conductive glass substrates were sequentially cleaned with detergent solution, deionized water, and anhydrous ethanol under ultrasonication for 20 min each, followed by drying with high-purity nitrogen and UV-ozone treatment for 30 min. For the hole transport layer, I spin-coated a 4PADCB solution (0.5 mg·mL⁻¹ in isopropanol) at 5000 rpm for 30 s and annealed at 100 °C for 10 min. The perovskite precursor solution was prepared with a composition of 0.05FA0.85MA0.1PbI3 at 1.7 mol·L⁻¹ in DMF/DMSO (4:1 v/v), with additives including 0.5% PMAI, 10% MACl, and 5% PbI₂. The solution was filtered through a 0.45 μm PTFE filter before use. I spin-coated 60 μL of the precursor at 1000 rpm for 7 s and then at 5000 rpm for 30 s, with 190 μL chlorobenzene antisolvent dripped at 17–18 s during the high-speed step. The wet film was annealed at 100 °C for 30 min. For the A12C4 passivation layer, I dissolved A12C4 in chlorobenzene at concentrations of 0.3, 0.5, 0.75, and 1 mg·mL⁻¹, then dynamically spin-coated 70 μL at 5000 rpm for 35 s, followed by annealing at 110 °C for 10 min. Finally, I thermally evaporated 30 nm C60, 8 nm BCP, and 100 nm Cu through a shadow mask, defining an active area of 0.0736 cm². All fabrication steps were performed in a high-purity nitrogen glovebox, except for the thermal evaporation and substrate cleaning.
For material characterization, I used ¹H nuclear magnetic resonance (NMR) spectroscopy to probe coordination between A12C4 and PbI₂. X-ray photoelectron spectroscopy (XPS) was employed to analyze chemical shifts of O 1s, N 1s, and Pb 4f core levels. X-ray diffraction (XRD) was used to examine phase composition and residual PbI₂. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) provided surface morphology and roughness information. Water contact angle measurements assessed surface hydrophobicity. Steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL), and PL mapping were performed to evaluate defect passivation and carrier recombination. Ultraviolet-visible (UV-vis) absorption spectroscopy and Tauc analysis determined the optical bandgap. Ultraviolet photoelectron spectroscopy (UPS) was used to determine work function and valence band maximum. Current density-voltage (\(J\)-\(V\)) curves, dark \(J\)-\(V\) curves, transient photocurrent (TPC), and transient photovoltage (TPV) measurements were conducted to evaluate device performance and charge carrier dynamics. Stability tests included steady-state power output at the maximum power point and thermal stability under dark nitrogen atmosphere at 65 °C for unencapsulated devices.
Interaction Between A12C4 and Perovskite Surface
To verify the coordination interaction between A12C4 and PbI₂, I first performed ¹H NMR spectroscopy. When PbI₂ was introduced into the A12C4 solution, the characteristic proton signals of A12C4 exhibited clear downfield shifts. This low-field displacement indicates that the local chemical environment of the protons changed due to coordination. The oxygen and nitrogen atoms in A12C4 act as Lewis base sites and donate electron density to Pb²⁺. This coordination reduces the electron cloud density around the adjacent protons, causing a deshielding effect and a downfield shift in the ¹H NMR spectrum. The observation confirms that A12C4 can interact with Pb²⁺ species, which is the first requirement for defect passivation in perovskite solar cells.
I further used XPS to examine the chemical states at the perovskite surface before and after A12C4 treatment. The O 1s and N 1s peaks shifted toward higher binding energies after A12C4 modification. This shift indicates that the O and N atoms donate their lone pair electrons to the empty orbitals of undercoordinated Pb²⁺, forming Lewis acid-base coordination bonds. Concurrently, the Pb 4f peaks shifted toward lower binding energy, suggesting that the electron density around Pb atoms increased due to coordination. These XPS results provide direct evidence that A12C4 molecules coordinate with surface Pb²⁺ and passivate related defects in perovskite solar cells. The coordination can be conceptually described by the following equilibrium:
$$ \text{Pb}^{2+}_{\text{surface}} + \text{A12C4} \rightleftharpoons [\text{Pb}^{2+} \cdots \text{A12C4}]_{\text{adduct}} $$
The formation of this adduct reduces the number of undercoordinated Pb²⁺ sites, which are known to introduce deep-level traps in perovskite solar cells. The passivation effect is expected to lower non-radiative recombination and improve device performance. I also note that the secondary amine nitrogen in A12C4 has stronger Lewis basicity than ether oxygen, which may enhance the coordination strength with Pb²⁺. The combined action of multiple O and N donor sites within the crown ether ring may provide a multidentate coordination environment, further stabilizing the surface and improving the robustness of perovskite solar cells.
Table 1 summarizes the XPS peak shift directions observed for the relevant core levels. Although the magnitudes of the shifts are not listed here, the directions consistently support the proposed coordination mechanism. The O 1s and N 1s shifts to higher binding energy reflect electron donation from A12C4 to Pb²⁺, while the Pb 4f shift to lower binding energy reflects increased electron density at Pb sites. This complementary behavior is characteristic of Lewis acid-base interactions and confirms that A12C4 is an effective passivator for perovskite solar cells.
| Core level | Shift direction after A12C4 | Interpretation |
|---|---|---|
| O 1s | Higher binding energy | O lone pair donation to Pb²⁺ |
| N 1s | Higher binding energy | N lone pair donation to Pb²⁺ |
| Pb 4f | Lower binding energy | Increased electron density around Pb |
Film Morphology, Crystallinity, and Surface Properties
I examined the crystalline phase evolution of the perovskite films using XRD. The control film exhibited a prominent diffraction peak near 12.78°, which corresponds to residual PbI₂. This indicates a non-stoichiometric lead iodide enrichment at the surface and grain boundaries. Residual PbI₂ can create structural discontinuities and compositional heterogeneity, leading to high-density defect states such as undercoordinated Pb²⁺ and Pb⁰ clusters. These defects act as charge trapping centers and exacerbate non-radiative recombination in perovskite solar cells. After A12C4 modification, the PbI₂ diffraction peak was significantly weakened. This change confirms the physicochemical role of A12C4 in passivating interfacial defects. Through Lewis acid-base coordination, A12C4 captures dangling Pb²⁺ ions and, via surface coverage, mitigates structural distortion and non-ideal phase formation at grain boundaries. The reduction of residual PbI₂ is beneficial for both charge transport and stability of perovskite solar cells.
To further understand the microstructural changes, I performed top-view SEM and AFM measurements. The control film showed non-uniform grains, scattered small crystallites, and bright residual PbI₂ phases at grain boundaries. In contrast, the A12C4-modified film exhibited highly uniform morphology. The original grain boundary roughness and localized microvoids disappeared, replaced by smooth, continuous, and large-grained domains. I attribute this morphological improvement to two synergistic effects. First, during dynamic spin coating, solvent washing and shear forces selectively remove small, poorly crystallized, or weakly bound grains and some residual PbI₂ phases. Second, A12C4 molecules coordinate with undercoordinated Pb²⁺ at grain boundaries and surfaces, reducing defect density and promoting local structural reconstruction. This leads to a smoother and denser surface. Such a compact and defect-free surface is expected to reduce interfacial recombination and act as a physical barrier against water and oxygen ingress in perovskite solar cells.
AFM analysis quantified the surface roughness changes. The control film had a root-mean-square (RMS) roughness of 26.2 nm, with noticeable height fluctuations and sharp protrusions. After A12C4 passivation, the RMS roughness decreased to 22.3 nm, indicating a smoother and more continuous surface. This smoother surface can facilitate uniform deposition of C60 molecules, forming a dense and continuous electron transport layer. The improved interface structure promotes electron extraction and transport while reducing the probability of interfacial carrier recombination in perovskite solar cells. Therefore, the morphological improvement is expected to contribute positively to the electrical performance of the devices.
I also evaluated the surface wettability by water contact angle measurements. The control film exhibited a water contact angle of 64.9°, while the A12C4-modified film showed an increased contact angle of 83.9°. The enhanced hydrophobicity confirms the formation of an ordered A12C4 molecular overlayer on the perovskite surface. The increased surface hydrophobicity can hinder water penetration into the film, weakening water-induced structural degradation and improving the operational stability of perovskite solar cells under ambient conditions. Table 2 summarizes the morphology and surface property parameters before and after A12C4 treatment.
| Parameter | Control | A12C4-modified | Change |
|---|---|---|---|
| RMS roughness (nm) | 26.2 | 22.3 | Decreased |
| Water contact angle (°) | 64.9 | 83.9 | Increased |
| Residual PbI₂ XRD peak | Strong | Weak | Suppressed |
| Surface morphology | Non-uniform, microvoids | Uniform, compact | Improved |
Carrier Dynamics and Energy Level Regulation
To investigate carrier recombination dynamics at the A12C4-modified interface, I performed steady-state PL and TRPL measurements. The A12C4-treated film exhibited stronger PL intensity than the control film. This enhancement is attributed to effective passivation of non-radiative recombination centers by A12C4. In perovskite solar cells, stronger PL intensity generally indicates reduced trap-assisted recombination and improved radiative efficiency. I then analyzed the TRPL decay curves using a double-exponential function:
$$ I(t) = A_1 \exp\left(-\frac{t}{\tau_1}\right) + A_2 \exp\left(-\frac{t}{\tau_2}\right) $$
where \(\tau_1\) and \(\tau_2\) are the fast and slow decay lifetimes, respectively, and \(A_1\) and \(A_2\) are the corresponding amplitudes. The average lifetime \(\tau_{avg}\) was calculated using:
$$ \tau_{avg} = \frac{A_1 \tau_1^2 + A_2 \tau_2^2}{A_1 \tau_1 + A_2 \tau_2} $$
The fitting results are summarized in Table 3. The control film had an average lifetime of 6.38 μs, while the A12C4-modified film exhibited an average lifetime of 12.42 μs. The nearly doubled carrier lifetime indicates that A12C4 effectively suppresses non-radiative recombination and reduces carrier trapping in perovskite solar cells. This improvement is consistent with the reduced surface defect density revealed by XPS and XRD. The prolonged lifetime is expected to enhance charge collection and improve the open-circuit voltage of perovskite solar cells.
| Sample | A₁ | τ₁ (μs) | A₂ | τ₂ (μs) | τ_avg (μs) |
|---|---|---|---|---|---|
| Control | 0.82 | 0.09 | 0.18 | 6.79 | 6.38 |
| A12C4-modified | 0.47 | 1.67 | 0.53 | 13.59 | 12.42 |
I further evaluated the uniformity of A12C4 passivation using PL mapping over a 20 μm × 20 μm area. The control film showed low and non-uniform PL intensity with numerous dark regions corresponding to defect-rich areas. After A12C4 modification, the average PL intensity increased significantly, and the signal distribution became highly uniform. This indicates that A12C4 achieves全域 uniform passivation of the perovskite surface, effectively suppressing local non-radiative recombination. The uniform passivation is crucial for large-area perovskite solar cells and modules, where spatial heterogeneity often limits performance.
I also measured UV-vis absorption spectra to examine whether A12C4 modification affects the intrinsic band structure. The absorption spectra of the control and A12C4-modified films were nearly identical, with no obvious difference in absorption onset or intensity. Using Tauc analysis, I estimated the optical bandgap from the absorption edge:
$$ (\alpha h\nu)^2 = A(h\nu – E_g) $$
where \(\alpha\) is the absorption coefficient, \(h\nu\) is the photon energy, \(A\) is a constant, and \(E_g\) is the optical bandgap. Both samples exhibited an optical bandgap of approximately 1.55 eV. This result confirms that A12C4 surface passivation does not significantly alter the intrinsic band structure of the perovskite absorber. Therefore, the performance improvement originates from interface modification rather than a change in the bulk bandgap of perovskite solar cells.
To investigate interfacial energy level regulation, I performed UPS measurements. The secondary electron cutoff was used to determine the work function according to:
$$ \phi = h\nu – E_{cutoff} $$
where \(h\nu\) is the photon energy (He I, 21.22 eV) and \(E_{cutoff}\) is the secondary electron cutoff energy. The work function decreased from 4.35 eV for the control film to 3.99 eV for the A12C4-modified film. The valence band maximum (VBM) shifted from 5.45 eV to 5.35 eV. Combining these values with the optical bandgap of 1.55 eV, I calculated the conduction band minimum (CBM) using:
$$ E_{CBM} = E_{VBM} + E_g $$
The CBM changed from 3.90 eV for the control film to 3.80 eV for the A12C4-modified film. The corresponding energy level alignment is summarized in Table 4. After A12C4 interface passivation, the energy level matching between the perovskite CBM and the electron transport layer was optimized, effectively reducing the interfacial electron injection barrier. The energy level regulation is mainly attributed to coordination adsorption of A12C4 on the perovskite surface. The lone pair electrons from O and N atoms coordinate with undercoordinated Pb²⁺, inducing surface charge redistribution and forming an interfacial dipole layer. This process shifts the surface Fermi level toward the conduction band, exhibiting n-type doping characteristics, thereby optimizing the interfacial energy level structure and improving band alignment with the adjacent transport layer. Such energy level optimization facilitates efficient extraction and transport of photogenerated electrons to the ETL, providing strong support for enhanced performance of perovskite solar cells.
| Parameter | Control | A12C4-modified |
|---|---|---|
| Work function (eV) | 4.35 | 3.99 |
| VBM (eV) | 5.45 | 5.35 |
| Optical bandgap (eV) | 1.55 | 1.55 |
| CBM (eV) | 3.90 | 3.80 |
Photovoltaic Performance of Perovskite Solar Cells
Based on the surface passivation, energy level regulation, and carrier dynamics optimization described above, I fabricated inverted perovskite solar cells with the structure FTO/4PADCB/perovskite/A12C4/C60/BCP/Cu. I systematically evaluated the photovoltaic performance of devices prepared with different A12C4 concentrations (0.3, 0.5, 0.75, and 1 mg·mL⁻¹). For each concentration, I analyzed 20 independent devices. The statistical results showed that A12C4 modification improved all photovoltaic parameters, including \(V_{OC}\), short-circuit current density (\(J_{SC}\)), fill factor (\(FF\)), and power conversion efficiency (\(PCE\)). The best performance and the narrowest distribution were obtained at an A12C4 concentration of 0.5 mg·mL⁻¹. At this optimal concentration, the devices exhibited the highest \(V_{OC}\), \(FF\), \(J_{SC}\), and \(PCE\), indicating effective passivation and energy level optimization without detrimental aggregation or insulating effects. Table 5 summarizes the trend of photovoltaic parameters with A12C4 concentration.
| A12C4 concentration (mg·mL⁻¹) | V_OC trend | J_SC trend | FF trend | PCE trend |
|---|---|---|---|---|
| 0.3 | Improved | Improved | Improved | Improved |
| 0.5 | Best | Best | Best | Best |
| 0.75 | Slightly lower | Slightly lower | Slightly lower | Slightly lower |
| 1.0 | Lower | Lower | Lower | Lower |
The optimal device achieved a \(PCE\) of 25.38%, with \(V_{OC}\) = 1.185 V, \(J_{SC}\) = 25.40 mA·cm⁻², and \(FF\) = 84.33%. In comparison, the control device exhibited a \(PCE\) of 24.25%, \(V_{OC}\) = 1.172 V, \(J_{SC}\) = 25.16 mA·cm⁻², and \(FF\) = 82.26%. The improvement in all parameters is attributed to A12C4 interface modification, which passivates surface defects and optimizes energy level alignment, enhancing electron transport in perovskite solar cells. The dark \(J\)-\(V\) curves showed that the A12C4-modified device had lower dark current, further confirming interface passivation and reduced leakage current. Table 6 presents the forward and reverse scan \(J\)-\(V\) parameters for the control and optimal A12C4-modified devices.
| Device | Scan direction | V_OC (V) | FF (%) | J_SC (mA·cm⁻²) | PCE (%) |
|---|---|---|---|---|---|
| Control | Forward | 1.166 | 80.15 | 25.12 | 23.47 |
| Control | Reverse | 1.172 | 82.26 | 25.16 | 24.25 |
| A12C4-modified | Forward | 1.176 | 83.46 | 25.37 | 24.90 |
| A12C4-modified | Reverse | 1.185 | 84.33 | 25.40 | 25.38 |
To gain deeper insight into charge extraction and recombination dynamics, I performed TPC and TPV measurements. The TPC decay curves were fitted with a single-exponential function, and the results are shown in Table 7. The control device had a decay lifetime of 0.52 μs, while the A12C4-modified device exhibited a shorter decay lifetime of 0.32 μs. This indicates that photogenerated carriers are extracted from the perovskite active layer to the C60 electron transport layer more rapidly after A12C4 modification. The improved dynamics are attributed to optimized energy level alignment and contact properties at the perovskite/C60 interface, which reduce the interfacial barrier and shorten carrier residence time at the interface. The TPV decay curves were also fitted, and the results are shown in Table 8. The control device had a photovoltage decay time of 0.95 μs, which increased to 2.88 μs after A12C4 treatment. The significantly prolonged carrier recombination lifetime indicates that A12C4 interface passivation effectively suppresses charge recombination inside the device. These results collectively demonstrate that A12C4 modification enhances charge extraction and reduces recombination in perovskite solar cells.
| Sample | A₁ | τ₁ (μs) |
|---|---|---|
| Control | 1.03 | 0.52 |
| A12C4-modified | 1.04 | 0.32 |
| Sample | A₁ | τ₁ (μs) |
|---|---|---|
| Control | 0.97 | 0.95 |
| A12C4-modified | 1.02 | 2.88 |
Operational and Thermal Stability
I evaluated the working stability of the perovskite solar cells by measuring the steady-state power conversion efficiency output at the maximum power point. The A12C4-modified device was held at a constant bias of 1.04 V, and its \(PCE\) remained stable at approximately 24.55% over 600 s. In contrast, the control device exhibited a clear downward trend in \(PCE\) over the same period. The stable output indicates that A12C4 passivation improves the operational stability of perovskite solar cells, likely due to reduced defect density and suppressed ion migration at the interface. The enhanced hydrophobicity also limits moisture ingress, contributing to the improved stability.
I further studied the thermal stability of unencapsulated devices by storing them in the dark under nitrogen atmosphere at 65 °C. After 100 h, the A12C4-modified device retained 93.0% of its initial \(PCE\), whereas the control device retained only 79.7%. The improved thermal stability is attributed to the robust coordination between A12C4 and the perovskite surface, which stabilizes undercoordinated Pb²⁺ and reduces residual PbI₂. The A12C4 overlayer also acts as a protective barrier that suppresses surface degradation and ion migration. These results demonstrate that A12C4 interface engineering not only enhances the efficiency but also improves the long-term stability of perovskite solar cells. Table 9 summarizes the stability data.
| Test condition | Control | A12C4-modified |
|---|---|---|
| Steady-state PCE over 600 s | Decreasing | Stable at ~24.55% |
| Thermal stability at 65 °C, 100 h | 79.7% retention | 93.0% retention |
Discussion
The results presented above demonstrate that A12C4 is a highly effective interfacial modifier for inverted perovskite solar cells. The molecule combines multiple Lewis base sites within a single cyclic structure, enabling multidentate coordination with surface Pb²⁺. This coordination passivates undercoordinated Pb²⁺ defects and eliminates residual PbI₂, which are major sources of non-radiative recombination in perovskite solar cells. The XPS and NMR results provide direct evidence of coordination, while XRD and SEM confirm the removal of residual PbI₂ and the formation of a dense, uniform film. The increased water contact angle indicates improved hydrophobicity, which is beneficial for stability against moisture. The PL and TRPL results show suppressed non-radiative recombination and prolonged carrier lifetime, consistent with reduced defect density. PL mapping further confirms uniform passivation across the film surface, which is important for large-area perovskite solar cells.
The UPS results reveal that A12C4 modification shifts the work function and valence band maximum, leading to better energy level alignment with the electron transport layer. The conduction band minimum is lowered from 3.90 eV to 3.80 eV, reducing the electron injection barrier. This energy level optimization is attributed to the formation of an interfacial dipole layer induced by coordination. The improved energy level alignment facilitates electron extraction and transport, as confirmed by TPC measurements showing faster carrier extraction. The TPV results show longer recombination lifetime, indicating that the passivation effect suppresses recombination losses. The combination of defect passivation and energy level regulation explains the improved \(V_{OC}\), \(J_{SC}\), \(FF\), and \(PCE\) of the A12C4-modified perovskite solar cells. The best device achieved a \(PCE\) of 25.38%, which is among the highest reported for inverted perovskite solar cells with crown ether-based interface modifiers.
The stability enhancement is equally important. The A12C4-modified device exhibited stable power output over 600 s and retained 93.0% of its initial efficiency after 100 h at 65 °C. The control device degraded more severely under the same conditions. The improved stability is attributed to the robust coordination bonds that stabilize the perovskite surface, the hydrophobic A12C4 overlayer that repels moisture, and the reduced defect density that suppresses ion migration. These factors collectively contribute to the enhanced operational and thermal stability of perovskite solar cells. The strategy presented here is compatible with scalable fabrication processes, as the A12C4 layer is deposited by a simple spin-coating step from an orthogonal solvent, which does not dissolve the underlying perovskite film.
In the context of perovskite solar cells, interface engineering is a powerful approach to overcome the trade-off between efficiency and stability. Many passivation molecules only address one aspect, such as defect passivation or energy level tuning. A12C4, however, provides a synergistic solution. The crown ether ring can coordinate with multiple Pb²⁺ sites, while the secondary amine nitrogen offers stronger Lewis basicity than oxygen. The cyclic structure may also provide steric hindrance that protects the surface. The dual function of A12C4 makes it an attractive candidate for commercialization of perovskite solar cells. Future work could explore the application of A12C4 in tandem devices, flexible perovskite solar cells, and large-area modules. The molecule could also be combined with other interface modifiers to further improve performance and stability.
Conclusion
I developed a synergistic interface engineering strategy based on the heteroatom-rich crown ether derivative A12C4 for inverted perovskite solar cells. A12C4 contains multiple ether oxygen atoms and a secondary amine nitrogen atom that can coordinate with undercoordinated Pb²⁺ on the perovskite surface. This coordination passivates surface defects, eliminates residual PbI₂, and improves film compactness and hydrophobicity. It also induces interfacial dipole formation and optimizes the energy level alignment between the perovskite and the electron transport layer, reducing the electron injection barrier. As a result, non-radiative recombination is suppressed, carrier lifetime is prolonged, and charge extraction is enhanced. The optimal device achieved a power conversion efficiency of 25.38%, with an open-circuit voltage of 1.185 V, a short-circuit current density of 25.40 mA·cm⁻², and a fill factor of 84.33%. The A12C4-modified perovskite solar cells also exhibited improved operational and thermal stability, retaining 93.0% of their initial efficiency after 100 h at 65 °C. This work demonstrates that A12C4 is a promising interface modifier for high-performance and stable perovskite solar cells. The dual function of defect passivation and energy level regulation provides a valuable design principle for future interface engineering in perovskite solar cells.
Overall, my findings highlight the importance of molecular design in interface engineering for perovskite solar cells. By selecting molecules with multiple Lewis base sites and appropriate steric and electronic properties, it is possible to simultaneously address surface defects and energy level mismatch. A12C4 serves as a proof-of-concept for this approach. The simple solution processing and orthogonal solvent compatibility make it suitable for scalable manufacturing. I believe that further optimization of crown ether derivatives and their application in tandem and large-area perovskite solar cells will accelerate the commercialization of this promising photovoltaic technology.