At the heart of this breakthrough lies the intricate interface between perovskite materials and tunnel oxide passivated contact (TOPCon) silicon wafers. Unlike traditional thicker silicon wafers, the thin wafers employed in tandem solar cells exhibit a unique combination of reduced thermal mass alongside enhanced thermal conductivity. This dual characteristic accelerates heat transfer profoundly during the deposition of the perovskite subcell, resulting paradoxically in an adverse effect on the quality of the perovskite film. Specifically, the rapid thermal flux induces an expedited crystallization process of the perovskite layer, leading to morphological inconsistencies and ultimately compromising the efficiency of the solar cell assembly.

The challenge posed by this rapid crystallization phenomenon is far from trivial; it manifests as voids and non-uniformities within the perovskite layer, alongside the undesirable segregation of halide components. These structural and compositional defects cascade into elevated non-radiative recombination losses, significantly detracting from the power conversion efficiency (PCE) of the tandem solar cell. Notably, these shortcomings stem directly from the interplay between the wafer’s physical properties and the perovskite layer’s crystallization kinetics, underscoring the complex material science challenges inherent in tandem device fabrication.

Confronting this issue, researchers have introduced a novel approach that leverages the chemical properties of 2-mercaptobenzothiazole (MBT) as an additive during perovskite film formation. This molecule exhibits a fascinating dual-mode binding with organic cations in the perovskite matrix, serving to carefully modulate the crystallization dynamics. By acting as a molecular ‘rheostat’, MBT slows down the otherwise precipitous crystallization triggered by the wafer’s enhanced thermal conductivity, permitting a more controlled and defect-resistant perovskite growth.

The impact of MBT on film morphology is significant: the additive fosters improved uniformity across the perovskite layer while simultaneously eliminating voids and suppressing the halide segregation phenomenon that had previously jeopardized film performance. This refined structural control contributes to a drastic reduction in trap-assisted recombination pathways. Demonstratively, the trap-assisted recombination rate declines from an alarming 3.2 × 10^5 cm s^−1 to a markedly improved 4.3 × 10^4 cm s^−1, signaling a substantial mitigation of non-radiative losses and implying improved charge carrier lifetimes within the active layer.

This molecular engineering approach does more than just improve film quality; it fundamentally boosts the device-level metrics of tandem solar cells integrating perovskite on industrial TOPCon silicon wafers. The two-terminal monolithic tandem devices fabricated using this technology have achieved a certified stabilized PCE of 32.76%, a remarkable milestone that positions such tandem cells at the forefront of solar efficiency benchmarks. Beyond raw efficiency improvements, these cells exhibit impressive operational stability, maintaining 91% of their initial efficiency after 1,700 hours of continuous illumination under standard testing conditions, underscoring their robustness for practical deployment.

From a technological perspective, this work exposes a previously underestimated crystallization problem specific to the interface of industrial silicon wafers and perovskite layers. The revelation not only deepens the fundamental understanding of perovskite crystallization under realistic fabrication conditions but also equips scientists and engineers with actionable strategies to integrate perovskite solar cells more seamlessly into the existing silicon photovoltaic infrastructure. Such integration is crucial if perovskite-based devices are to transition from laboratory prototypes to widespread commercial applications.

Moreover, the insights gained here pertain specifically to the unique thermal environment experienced by perovskite films on thin, thermally conductive silicon wafers, a scenario increasingly relevant as the industry moves towards thinner, more efficient silicon backbones. By addressing the root causes of rapid crystallization kinetics, researchers could circumvent the need for complex processing modifications or lower-throughput fabrication steps, thereby preserving scalability and cost-effectiveness.

This nuanced control over perovskite film formation through dual-mode chemical binding represents a bridge between the granular molecular chemistry of active layer materials and large-scale device engineering. It illustrates how additive chemistry can be harnessed to tune perovskite crystallization in pathways previously inaccessible, highlighting a crucial link between materials science and renewable energy technology development.

The ramifications of these findings extend beyond perovskite-TOPCon tandem solar cells. By illuminating mechanisms by which thermal properties of substrates influence perovskite layer quality, the study sets a precedent for tailoring interfaces in other layered photovoltaic architectures. Future explorations may seek to identify additional additives with similar or enhanced dual-binding characteristics or explore synergistic effects with co-additives to further elevate efficiency and operational stability.

Crucially, the reported advancements also hold promise for addressing long-standing concerns regarding the environmental stability of perovskite solar cells. The enhanced morphological uniformity and suppressed ion segregation inherently contribute to improved resilience under prolonged operational conditions, a key parameter for real-world energy production scenarios.

Industry stakeholders and academic researchers alike will find in this work a compelling demonstration of how subtle chemical modifications can unlock performance gains that are otherwise unattainable due to the physical constraints imposed by device architecture and material properties. The successful certification of high-efficiency tandem cells marks an important validation step toward commercialization, signaling that perovskite-silicon tandem solar cells are not merely experimental novelties but tangible energy solutions on the cusp of market readiness.

Looking forward, this pioneering strategy presents a foundational platform upon which future innovations can build. By continuing to refine the chemistry at the perovskite-silicon interface and understanding the dynamic thermal processes shaping crystallization, the photovoltaic community is poised to further enhance the integration of emergent materials with conventional technologies, enabling the next generation of high-efficiency, cost-effective, and durable solar energy devices.

In essence, the introduction of 2-mercaptobenzothiazole as a crystallization modulator has addressed a critical bottleneck in tandem solar cell fabrication, opening new avenues for the realization of ultra-efficient perovskite/silicon tandem photovoltaic modules. This advance symbolizes the power of targeted molecular design in solving complex fabrication challenges, propelling solar energy technologies toward higher efficiency thresholds and broader adoption in the global renewable energy landscape.

Subject of Research:
Additive-assisted modulation of perovskite crystallization dynamics on industrial tunnel oxide passivated contact (TOPCon) silicon wafers to boost tandem solar cell efficiency and stability.

Article Title:
Additive-assisted perovskite crystallization on industrial TOPCon silicon for tandem solar cells with improved efficiency.

Article References:
Zhou, Q., Guo, R., Liu, S. et al. Additive-assisted perovskite crystallization on industrial TOPCon silicon for tandem solar cells with improved efficiency. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02010-z

DOI:
https://doi.org/10.1038/s41560-026-02010-z

At the heart of perovskite photovoltaics lies a crystal lattice that is far from the rigid and harmonic frameworks found in classical semiconductors. Instead, metal halide perovskites exhibit highly anharmonic lattice vibrations, meaning their atoms do not oscillate around equilibrium positions in simple, predictable ways. Such anharmonicity leads to significant phonon–phonon interactions which profoundly impact thermal transport, expansion, and ultimately, the structural stability of the material. These complex vibrational behaviors allow perovskite lattices to undergo extreme thermal expansion, a property that, while fundamental, poses substantial challenges when integrating these materials into multilayer solar cell devices.

The phenomenon of thermal expansion in metal halide perovskites manifests in ways that deviate dramatically depending on crystallographic phase, temperature, and material composition. For instance, as the temperature increases, perovskites experience not only volumetric expansion but also directional dependencies that lead to anisotropic expansion. This means that the lattice can expand more along specific axes, and under certain conditions, even contract in another—a behavior termed negative thermal expansion. This finding is profoundly significant because such anisotropy and counterintuitive contraction can induce mechanical stresses and strains within the solar cell architecture.

One critical consequence of these lattice dynamics is the recurring thermal strain that arises during typical environmental cycling. In real-world applications, perovskite solar cells endure repeated heating during daylight hours and subsequent cooling at night. This cyclical thermal variation causes cumulative mechanical stress due to the lattice’s extreme and anisotropic thermal expansion properties. Over time, this stress can nucleate defects within the perovskite absorber layer, exacerbate defect migration, and accelerate material degradation, directly impacting the longevity and performance consistency of perovskite-based solar modules.

To bridge the knowledge gap between microscopic lattice behavior and macroscopic device failure, recent research has meticulously mapped atomistic anharmonic lattice dynamics in metal halide perovskites to their larger scale thermal and mechanical properties. Detailed investigations of phonon–phonon interactions have uncovered how these interactions distribute vibrational energy and promote localized dynamic disorder, which destabilizes the lattice framework under stress. This granular understanding lays the groundwork for comprehending how dynamic lattice fluctuations propagate to macroscopic thermal expansion phenomena.

The study of how anharmonicity and thermal expansion rates evolve across temperature regimes has revealed critical insights into the stability windows for various perovskite phases. For instance, at lower temperatures, perovskites tend to stabilize in more symmetric crystalline phases with relatively subdued anharmonic vibrations. Conversely, at elevated temperatures, transitions to low-symmetry phases are accompanied by pronounced anharmonic lattice vibrations, resulting in the emergence of complex thermal expansion behavior, including the surprising negative thermal expansion along certain crystallographic directions. This complexity demands that device engineers carefully consider phase stability in tandem with operating temperature when designing perovskite solar cells.

Chemical composition emerges as another pivotal factor modulating lattice dynamics and thermal expansion. Varying the halide composition or incorporating different metal cations systematically adjusts the degree of anharmonicity and the resultant thermal expansion coefficients within the lattice. Tailoring such compositional parameters enables targeted control over thermomechanical properties, allowing material scientists to optimize perovskite formulations that balance high performance with enhanced structural durability under thermal cycling conditions.

The discovery and characterization of anisotropic and negative thermal expansion phenomena also challenge traditional device design paradigms. Conventional photovoltaic architectures assume near-isotropic thermal behavior of materials, designing interfaces and encapsulations accordingly. However, perovskites’ anisotropic expansion introduces directionally dependent mechanical stresses at interfaces with other device layers—substrates, electron transport layers, and encapsulant materials—that differ markedly in thermal expansion coefficients. This mismatch exacerbates delamination risks and fracture formation, directly undermining device reliability.

Addressing these challenges necessitates a multi-scale approach that integrates atomistic insights with engineered device-level solutions. Strategies such as incorporating buffer layers to alleviate thermal mismatch, designing compliant interlayers with adjustable mechanical properties, and engineering perovskites at the molecular level to reduce anharmonic vibrational modes represent promising avenues. These approaches seek to regulate thermal strain, mitigate dynamic disorder, and suppress defect formation pathways that degrade perovskite solar cells over time.

Furthermore, understanding the atomistic basis of lattice dynamics offers exciting opportunities for predictive modeling of perovskite behavior under diverse environmental conditions. Advanced computational methods that accurately simulate anharmonic phonon interactions and phase transitions provide invaluable tools for forecasting perovskite stability and informing materials design before experimental fabrication, accelerating the path toward durable, high-efficiency photovoltaic technologies.

In essence, the convergence of fundamental physics with device engineering is setting the stage for transformative advances in perovskite photovoltaics. By elucidating the complicated anharmonic lattice dynamics and their thermal-structural consequences, researchers now can tackle the perennial problem of accelerated degradation under thermal cycling. This scientific framework promises not only to extend the lifetime of perovskite solar cells but also to unlock novel materials design paradigms that could redefine the limits of solar energy conversion efficiency and commercial viability.

While the road to fully commercialized, long-lasting perovskite solar cells is still evolving, the deepened understanding of their thermo-mechanical behavior marks a pivotal turning point. It paves the way for the engineering of perovskite absorbers that intelligently accommodate or leverage their intrinsic dynamic lattice properties, turning potential weaknesses into functional advantages. This ambitious vision heralds a new era where perovskite photovoltaics transcend laboratory curiosities to become robust pillars of sustainable energy infrastructure worldwide.

Ultimately, advancing perovskite photovoltaics demands persistent interdisciplinary collaboration—melding materials science, physics, chemistry, and engineering. The atomistic insights into lattice anharmonicity and thermal expansion provide a foundational knowledge base that will empower researchers and industry stakeholders to harmonize efficiency, stability, and manufacturability in perovskite solar cells, propelling these remarkable materials from experimental promise to renewable energy mainstays.

The future of perovskite photovoltaics rests on our ability to control and manage the complex lattice vibrations and thermal expansion properties that differentiate these materials from their conventional semiconductor counterparts. Progress in this arena opens exciting prospects not only for solar energy but also for broader applications where strain-engineered functional materials are desirable. By continuing to unravel the intricate atomic-scale phenomena driving large-scale device behavior, the photovoltaic community edges ever closer to realizing perovskites’ full technological potential.

Subject of Research: Atomistic lattice dynamics and thermo-mechanical properties in metal halide perovskites used for photovoltaics.

Article Title: Atomistic origins of anharmonic lattice dynamics and thermal expansion in perovskite photovoltaics.

Article References:
Steele, J.A. Atomistic origins of anharmonic lattice dynamics and thermal expansion in perovskite photovoltaics. Nat Energy (2026). https://doi.org/10.1038/s41560-025-01938-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-025-01938-y