Performance enhancement of perovskite solar cells for energy storage applications: Materials and device engineering

2.1.1. Solution method preparation of amino-functionalized silane monolayer and interfacial bonding regulation

(3-aminopropyl)triethoxysilane (APTES) is used as a self-assembly molecular precursor, and an isopropanol solution of appropriate concentration is prepared. After surface activation treatment, the perovskite film is immersed in the silane solution to form a dense monolayer. The silane molecules specifically bond with the defect sites on the perovskite surface through a hydrolysis condensation reaction. The process follows the Langmuir adsorption model Eq. (1):

Among them, $\Gamma$ represents the surface coverage. ${\Gamma }_{\max }$ reflects the maximum monolayer adsorption. ${\text{K}}_{\text{ads}}$ represents the adsorption equilibrium constant. C is the solution concentration. This model precisely controls the arrangement density of molecules at the interface to ensure that each active site is effectively passivated. Surface analysis technology confirms that amino groups form a stable coordination bond network with uncoordinated lead ions in the perovskite lattice, significantly reducing the density of interfacial dangling bonds.

The molecular layer reconstructs the interfacial chemical environment at the atomic scale to form a uniform electronic potential field distribution. Microstructural characterization shows that silane molecules selectively fill ion vacancies at the grain boundaries and block intrinsic migration channels. Dynamic ion tracking experiments confirm that the modified interface exhibits an excellent ion locking effect, effectively inhibiting component segregation driven by the electric field. The interface potential distribution test shows that the charge accumulation phenomenon is significantly alleviated, creating an ideal environment for carrier transport. X-ray photoelectron spectroscopy (XPS) analysis showed that the Pb 4f peak shifted to a lower binding energy direction by about 0.35 eV after APTES treatment, indicating that the amino group formed a coordinate bond with the uncoordinated Pb²⁺. At the same time, a characteristic peak of 399.2 eV appeared in the N 1s spectrum, corresponding to the N–Pb coordination structure, supporting the proposed ionic-bond-compensation mechanism.

Table 2 systematically summarizes the critical processing parameters and control criteria for interface modification via silane-based self-assembled monolayers (SAMs). In this study, APTES is employed as the precursor molecule. Its concentration is precisely regulated at the millimolar scale to guarantee the optimal surface coverage density of the monolayer. A high-purity isopropanol solvent system (purity ≥ 99.9%) is utilized to provide a favorable environment for the hydrolysis reaction. The immersion time is strictly confined to an 8–12 min window to ensure the completion of molecular self-assembly while preventing multilayer formation. The solution temperature is stably maintained at 25°C ± 0.5°C to preserve the stability of reaction kinetics. Post-treatment annealing is performed at 80°C–100°C to facilitate siloxane condensation and the formation of a robust covalently bonded network. All parameter ranges have been rigorously validated to ensure the construction of a highly ordered monolayer on the perovskite surface without inducing degradation of the underlying perovskite lattice. This established parameter framework offers standardized protocols for realizing reproducible interface engineering, thereby establishing a basis for subsequent device performance optimization. Notably, precise control over temperature and time is essential for fabricating uniform and compact molecular layers, and solvent purity directly governs the quality of the self-assembly process.

2.1.2. Band regulation and carrier dynamics optimization

While the silane molecular layer passivates defects, its terminal amino group induces the rearrangement of the interface dipole moment, achieving precise control of the band structure. The characteristic shift of the Fermi level position is observed through surface-sensitive energy spectroscopy technology, which significantly improves the energy level matching between the perovskite and the adjacent charge transfer layer. This optimization of the electronic structure significantly reduces the interface non-radiative recombination loss and improves the carrier extraction efficiency.

The carrier dynamics analysis follows the Shockley-Read-Hall recombination theory Eq. (2):

${\tau }_{eff}$ represents the effective carrier lifetime. $v_{th}$ is the thermal motion velocity. ${\sigma }_b$ represents the capture cross-section. $N_t$ reflects the trap density. The carrier lifetime is improved by an order of magnitude after interface modification, confirming that the defect-assisted recombination channel is effectively suppressed. Microstructural characterization combined with theoretical calculations reveals that the silane molecules form conformal contact with the perovskite lattice, maintaining the periodicity of the lattice while eliminating the local strain field.

The electron transport performance test shows that the interface contact resistance is significantly reduced, which is attributed to the improvement of band continuity and the reduction of potential energy barrier height. In-situ photoelectric characterization confirms that the modified device maintains a stable charge separation efficiency under continuous operating conditions, and no obvious interface degradation is observed. This robust interface structure provides an ideal platform for achieving efficient and stable carrier transport.

Carrier-dynamics characterization was conducted by time-resolved photoluminescence (TRPL), transient photovoltage (TPV), transient absorption spectroscopy (TAS), and electrochemical impedance spectroscopy (EIS). TRPL was measured using a 400 nm pulsed laser and a single-photon counting system with a temporal resolution of 50 ps under a dry N₂ atmosphere. TPV measurements were performed under AM 1.5 white-light bias with a lock-in amplifier at 25 ± 0.5°C. TAS was carried out using a tunable pump-probe system and a spectrometer array with a temporal resolution of 200 fs in a vacuum-sealed chamber. EIS measurements were conducted with a 10 mV AC perturbation over a frequency range of 0.1 Hz to 1 MHz under electromagnetic shielding conditions. All measurements were repeated three times to ensure reproducibility.

2.2.1. Interface energy band engineering of atomic layer deposited SnO₂ nanolayer

Plasma-enhanced atomic layer deposition technology is used to construct SnO₂ nanofilm on the surface of the silane-modified layer under the protection of an inert atmosphere. The alternating cycle of precursor pulses and plasma oxidation steps ensures the self-limiting surface reaction characteristics of film growth. During the deposition process, the reaction chamber temperature and plasma power are precisely controlled to achieve directional epitaxial growth of the SnO₂ lattice. The key to this process is to maintain a moderate oxygen vacancy concentration, which not only ensures the conductivity of the film but also avoids carrier recombination caused by excessive defects.

The regulation of the band structure follows the semiconductor heterojunction theory, and the continuous gradient of the work function is achieved by adjusting the stoichiometric ratio of SnO₂. The electronic structure characteristics of the film satisfy the following relationship Eq. (3):

$\varphi$ represents the work function. $\chi$ is the electron affinity. $E_c-E_F$ reflects the Fermi level position. Interfacial analysis suggests that the optimized SnO₂ layer forms favorable energy-level alignment with the underlying silane-modified layer, thereby facilitating electron transfer across the interface. Synchrotron-based characterization further indicates the presence of a nanoscale elemental interdiffusion region, suggesting the formation of an interfacial transition zone between the two layers. This interfacial structure is consistent with reduced interfacial-state density and improved electronic coupling. Ultraviolet photoelectron spectroscopy (UPS) shows that, after SnO₂/silane bilayer modification, the device work function increased from 4.21 eV to 4.48 eV, consistent with the proposed dipole-related band-bending effect at the interface. In addition, grazing-incidence XRD reveals that the full width at half maximum (FWHM) of the perovskite (110) diffraction peak decreased by 18%, suggesting partial relief of lattice strain after interfacial engineering.

Table 3 systematically summarizes the key process parameters and functional objectives of preparing SnO₂ nanolayers by plasma-enhanced atomic layer deposition. The precursor used is a combination of SnCl₄ and H₂O as a metal source and an oxidant, respectively, and layer-by-layer growth is achieved through alternating pulses. The deposition temperature is controlled in the range of 120°C-150°C, which can maintain sufficient precursor decomposition activity and avoid thermal damage to the perovskite substrate. The SnCl₄ pulse time is limited to 0.1s-0.3s to ensure that the precursor molecules reach saturated adsorption on the substrate surface without producing gas-phase side reactions. The purge time is set to 5s-8s, and the reaction byproducts are completely removed by high-purity nitrogen to ensure the chemical purity of the film and the steepness of the interface. The synergistic effect of various parameters forms a stable self-limiting surface reaction mechanism. Finally, a SnO₂ nano layer with uniform thickness and controllable stoichiometric ratio is obtained. This process window is optimized and verified by orthogonal experiments and shows excellent consistency in repeatability tests, laying the foundation for subsequent band engineering and stress regulation.

2.2.2. Mechanical stress coordination and interface stability enhancement

The stress buffering function of the SnO₂ nanolayer originates from its unique microstructure design. Controllable lattice strain is added during the film growth process, and the gradient distribution of the strain state is achieved by precisely controlling the deposition parameters. This strain engineering enables the SnO₂ layer to have excellent stress coordination ability. Its mechanical behavior can be described by the film elasticity theory Eq. (4):

${\sigma }_f$ is the actual stress. E is the elastic modulus. $\in$ represents strain. ${\sigma }_0$ represents the intrinsic stress. Through microstructural characterization, it is observed that the SnO₂ grains show a special columnar growth morphology, and there is an amorphous phase network in the grain boundary region. This multi-scale structure gives the film excellent mechanical adaptability.

With the action of thermomechanical stress, the SnO₂ buffer layer effectively dissipates stress through mechanisms such as lattice distortion and interface slip. In-situ testing technology confirms that the structure can significantly alleviate the interface stress concentration caused by differences in thermal expansion coefficients. Dynamic mechanical analysis shows that the SnO₂ layer significantly improves the interface binding energy and structural stability of the device under temperature cycling conditions. The unique microstructure of the film also gives the interface excellent resistance to crack propagation, providing a guarantee for the long-term stable operation of the device.

In Figure 2, the horizontal axis represents the interfacial depth (0–10 nm), and the vertical axis represents atomic concentration. The Sn profile shows a gradient distribution in the near-interface region, with a maximum concentration at approximately 2 nm. Its gradual decay is consistent with diffusion-controlled interfacial penetration, suggesting that plasma-assisted deposition promotes shallow incorporation of Sn species into the interfacial region. The Si concentration reaches a maximum of about 50% at around 3 nm, and its distribution extends slightly deeper than that of Sn, which may be associated with partial thermal dissociation and limited diffusion of silane species during deposition. The oxygen concentration decreases in the Sn-rich region, consistent with the growth of the SnO₂ layer, and increases again to approximately 65% in the silane-dominated region (>4 nm), indicating that the interfacial process does not cause excessive oxidation of the silane layer.

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Figure 2. (a-c) Depth analysis of interdiffusion of elements at the SnO₂/silane interface.

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The observed interdiffusion behavior appears to be governed by both the interfacial chemical potential gradient and the deposition energy. The shallow penetration of Sn may be related to interactions between deposited Sn species and terminal hydroxyl groups of the silane layer, which can promote interfacial anchoring. In contrast, the more limited diffusion of Si is likely constrained by the covalently cross-linked network of the silane molecular layer. These results suggest the formation of an interfacial transition region between the two materials. In addition, oxygen vacancies in the SnO₂ lattice may contribute to interfacial electronic regulation through interactions with amino-functional groups in the silane layer, which is consistent with the proposed dipole-related interfacial effect. Such an interlocked interfacial structure may help reduce defect density and alleviate thermal-expansion mismatch between heterogeneous layers. The spatial variation in oxygen concentration also suggests that the interfacial oxidation state remains reasonably controlled, which is beneficial for preserving charge-transport continuity across the interface.

2.3.1. Molecular penetration and interpenetration induced by dynamic thermocompression

The thermoplastic encapsulation colloid is rationally designed on the basis of reversible dynamic covalent chemistry, in which furan–maleimide reversible bonding moieties are incorporated into the molecular backbone. During the encapsulation process, the applied thermal gradient triggers the reversible cleavage and reformation of dynamic covalent bonds, endowing the colloid with adaptive flow characteristics in its viscoelastic state. A multi-stage pressure regulation protocol is implemented for the thermocompression procedure. In the initial phase, a moderate pressure is applied to induce viscoelastic deformation of the colloid, thereby filling microscale interfacial voids. Subsequently, a gradient pressure ramp drives the three-dimensional interpenetration of molecular chains, leading to the formation of a cross-scale interpenetrating network structure. The colloid flow behavior follows the constitutive relationship of non-Newtonian fluids Eq. (5):

$\tau$ is shear stress. $\eta$ represents the apparent viscosity. $\dot{\gamma }$ is the shear rate. n is the power law index. Temperature regulation realizes the transition of colloid from solid elastic response to viscous flow plastic behavior by changing the n value. In-situ spectral analysis confirms that the reversible behavior of dynamic covalent bonds promotes the topological reconstruction of molecular chains and forms an interface transition layer chemically bonded to the encapsulation substrate. Molecular dynamics simulation reveals that the terminal functional groups of the colloid form a hydrogen bond-covalent bond hybridization with the hydroxyl groups on the substrate surface, which significantly improves the interface binding energy.

The penetration depth of the colloid is optimized by regulating the interface morphology, and its filling efficiency is controlled by the synergistic effect of the thermocompression temperature field and pressure field. Microstructural characterization shows that the molecular chains formed a gradient entangled network in the interface area, effectively bridging the structural defects from the nanometer to micrometer scale. This molecular-level interlocking mechanism significantly inhibits the tendency of interface delamination and improves the mechanical robustness of the encapsulation system. After thermocompression, the free volume fraction of the interface area is significantly reduced, and the orientation degree and crystallinity of the molecular chains increase synergistically to form a dense barrier.

Table 4 systematically summarizes the key parameters of the dynamic thermocompression process and its regulation mechanism on the molecular penetration behavior. The thermocompression temperature was controlled within 80–100°C, and the pressure was gradually increased from 0.5 to 2 MPa to facilitate interfacial filling and structural rearrangement within the encapsulation stack. Rheological analysis was used to characterize the viscoelastic flow behavior of the encapsulant during processing, while focused ion beam cross-sectional profiling suggested effective filling of interfacial voids from the nanoscale to the microscale. Small-angle X-ray scattering results were consistent with a reduction in free volume and an increase in chain ordering after thermocompression, supporting the formation of a denser barrier structure. Overall, the combined temperature–pressure–shear regulation appears to improve interfacial cohesion and encapsulation compactness. The shear rate range covers 10⁻²s⁻¹-10¹s⁻¹. The power law characteristics of non-Newtonian fluids are quantified by the dynamic shear test of the rheometer, revealing the viscoelastic state transition law of the colloid during the thermocompression process. The molecular penetration depth is verified by focused ion beam profile analysis, showing the interface filling effect from the nanometer to the micrometer scale, effectively eliminating the structural defects between the encapsulation layers. Synchrotron radiation small-angle X-ray scattering analysis can show that the free volume of the colloid is reduced after thermocompression, and the orientation degree and crystallinity of the molecular chain are synergistically improved to form a dense barrier network. Through the multi-field coupling of the temperature-pressure-shear field, each parameter synergistically realizes molecular-level interface fusion and structural rearrangement, providing a theoretical basis and process support for the thermomechanical consistency and barrier performance of the encapsulation layer.

2.3.2. Structural evolution and performance regulation of thermomechanically adapted encapsulation layer

During the dynamic thermocompression process, a periodic mechanical oscillation field is used to induce structural rearrangement of the encapsulation layer through stress-temperature coupling. The colloidal crystallization behavior follows the strain-induced nucleation mechanism. Its kinetic process can be described by the modified Avrami equation Eq. (6):

$X\left(t\right)$ is the crystallinity. k is the rate constant. m reflects the nucleation growth mode parameter. The mechanical oscillation field changes the spatial distribution of nucleation sites, promoting heterogeneous nucleation and preferential growth of nanocrystals. Wide-angle X-ray diffraction shows that the colloidal molecular chains are arranged along a specific crystal direction to form a nanofiber reinforcement structure that runs through the interface. This anisotropic microstructure gives the encapsulation layer a gradient modulus property. The high crystallinity of the surface area provides rigid protection. The bottom layer retains moderate flexibility to buffer thermal stress.

Coefficient of thermal expansion (CTE) matching of the encapsulation layer is realized via precise modulation of molecular chain segment mobility. The gradient modulus structure effectively dissipates interfacial thermal stress and suppresses the initiation of microcracks induced by thermal cycling. The enhanced barrier performance originates from two synergistic mechanisms: molecular chain densification reduces free-volume pathways, while the oriented arrangement of crystalline domains constructs a tortuous diffusion pathway. Water and oxygen permeability measurements verify that the encapsulation layer exhibits a pronounced inhibitory effect on the adsorption and diffusion of polar molecules. Interfacial chemical-stability analysis suggests that the dynamic-bond network may help accommodate local structural imperfections generated during encapsulation, thereby contributing to sealing integrity during aging.

The thermocompression encapsulation system exhibited improved hygrothermal stability and mechanical robustness under the tested conditions. Taken together, the structural and aging results support the view that interfacial fusion and gradient-structure design contribute to enhanced protection of PSC devices across multiple length scales. Environmental aging tests further indicate that the fluorosilicone coating helps preserve edge integrity under humid-heat conditions, while its dynamic network may hinder crack propagation and slow the formation of permeation pathways. As a result, edge protection contributes to improved device stability during environmental exposure.

2.4.1. Gradient hydrophobic interface design of fluorosilicone copolymer coating

The sol-gel method and chemical vapor deposition synergistic process are used to construct a gradient cross-linked fluorosilicone copolymer coating on the surface of the encapsulation layer. The precursor is a mixed system of perfluoroalkylsiloxane and alkoxysilane. The hierarchical assembly of fluorocarbon chains and silicon-oxygen networks is achieved by precisely controlling the kinetics of the hydrolysis-condensation reaction. A lotus-like bionic micro-nanostructure is formed on the coating surface. Its hydrophobic properties follow the Cassie-Baxter wetting model Eq. (7):

${\theta }_c$ is the apparent contact angle. ${\theta }_Y$ is the intrinsic contact angle. $f_s$ is the solid-liquid contact area fraction. By increasing the density of the fluorocarbon chain by gradient, a dense fluorinated barrier is formed on the surface, and a highly cross-linked silicon-oxygen network is retained in the bottom layer to enhance mechanical strength. Molecular dynamics simulations show that the rigid orientation of the fluorocarbon chain and the flexible movement of the silicon-oxygen chain work together to form a dynamic hydrophobic interface: the fluorine atoms on the surface repel the adsorption of water molecules through the steric effect, and the silicon-oxygen bonds in the bottom layer reconstruct the interface stress through hydrogen bonds.

The chemical bonding characteristics of the coating are achieved through the interface transition layer. During the deposition process, the precursor molecules undergo condensation reactions with the active groups on the surface of the encapsulation layer to form an interpenetrating network connected by covalent bonds. This chemical anchoring effect significantly improves the adhesion of the coating and inhibits interfacial stratification in a humid and hot environment. Microstructural characterization confirms that the coating forms a continuous sealing layer on the edge of the encapsulation, effectively blocking the water and oxygen penetration path.

2.4.2. Dynamic thermomechanical adaptation and diffusion path blocking mechanism

The thermal expansion adaptability of fluorosilicone copolymers is derived from their dynamic covalent bond network design. Reversible disulfide bonds and siloxane units are used to achieve strain adaptation through the thermal response characteristics of the bonding state. The thermomechanical behavior of the material follows the modified Grüneisen relationship Eq. (8):

$\alpha$ is the coefficient of thermal expansion. ${\gamma }_g$ is the Grüneisen parameter. $C_v$ is the heat capacity at constant volume. $K_t$ is the bulk elastic modulus. $V_m$ is the molar volume. The reversible breaking and recombination of dynamic bonds enables the coating to actively regulate internal stress during temperature cycling: at high temperatures, the bonds dissociate and absorb expansion strain, and at low temperatures, the bonds reorganize and release contraction stress. Synchrotron radiation characterization shows that the microstructure of the coating remains highly stable under thermal shock, with no obvious phase separation or crack extension.

The permeation barrier function is achieved through the synergy of multi-scale structures. The high-density fluorocarbon chains on the surface construct a superhydrophobic interface, which significantly increases the activation energy of water molecule diffusion. The bottom gradient cross-linked network restricts molecular migration through free volume regulation. The diffusion kinetics behavior satisfies the modified Fick’s law Eq. (9):

$C_s$ is the concentration of the permeate. $D_k$ is the diffusion coefficient. $k_x$ is the adsorption rate constant. The low-polarity surface of the fluorosilicone coating inhibits the adsorption of water molecules, and the tortuous diffusion path prolongs the penetration time. Environmental aging tests show that the coating maintains stable interface integrity under humid and hot conditions, and its dynamic bond network can repair microcracks and block the expansion of the penetration channel. The enhanced protection of the encapsulation edge enables the device to maintain excellent performance stability in extreme environments.