Tandem solar cells (TSCs) are lauded for their potential to surpass the efficiency limitations of conventional single-junction solar devices by stacking two subcells with different bandgaps. Each subcell absorbs distinct segments of the solar spectrum, enabling more effective harnessing of sunlight. In the realm of all-perovskite tandem solar cells, however, practical implementation has faced formidable hurdles. Central among these challenges is the mismatched crystallization kinetics between the wide-bandgap (WBG) and narrow-bandgap (NBG) perovskite layers. This imbalance often leads to phase segregation and defect proliferation, detracting significantly from device efficiency and operational longevity.

To overcome these intrinsic difficulties, Professors GE Ziyi and LIU Chang, along with their research team, have devised a unified colloidal chemistry strategy that strikes a delicate balance in crystallization dynamics between the WBG and NBG perovskite subcells. This breakthrough leverages a meticulously designed modulation system based on graded carboxylate anions—specifically tartrate (Ta-) and citrate (Cit-) ions—that exert precise control over nucleation and crystal growth pathways in both subcells.

In the WBG subcell, the introduction of tartrate anions proves instrumental by stabilizing the coordination environment of Pb2+ ions. This stabilization suppresses unwanted phase segregation, fostering a more uniform and controlled crystalline lattice arrangement. Such uniformity is vital because it minimizes defect sites that can act as recombination centers for charge carriers, thus preserving the solar cell’s photovoltaic performance.

Conversely, in the NBG subcell—which typically suffers from Sn2+ defect states that act as non-radiative recombination centers—citrate anions play a dual role. They optimize Sn-I bonding within the colloidal precursor environment, effectively passivating the vulnerable Sn2+ defects. This passivation enhances the charge transport properties of the NBG layer, which is fundamental to maximizing the overall current output of the tandem device.

Amplifying the stabilizing effect, choline cations are introduced as synergistic agents, passivating undercoordinated metal ions at the interfaces between the crystal and colloid phases. This interface passivation is crucial for constructing a robust stabilization matrix that maintains heterojunction integrity during the critical nucleation and growth phases. The tailored colloidal precursor solution thus orchestrates a harmonized crystallization process across the tandem structure, ensuring optimized electronic and structural properties.

The resultant tandem solar cells demonstrate a phenomenal power conversion efficiency (PCE) of 29.76%, a value that is among the highest recorded for all-perovskite tandem architectures. Notably, this outstanding performance was independently certified with a measured PCE of 29.22%, underscoring the reproducibility and credibility of the method. The devices also showcase remarkable operational stability, sustaining over 90.2% of their initial efficiency after more than 700 hours of continuous exposure under maximum power point tracking—a rigorous test indicative of commercial viability.

Scaling up from lab-scale testing, the team fabricated a 1 cm² large-area tandem cell using their colloidal chemistry methodology. This larger device achieved a commendable PCE of 28.87%, demonstrating the strategy’s potential for practical deployment in industrial-scale photovoltaic manufacturing processes. The scalability factor is particularly significant because it addresses a fundamental bottleneck in transitioning high-efficiency perovskite technology from academic laboratories to accessible green energy solutions.

Beyond immediate performance gains, this research contributes a universal framework for tuning multijunction crystallization kinetics via chemical modulation. By aligning nucleation rates and mechanisms between the dissimilar perovskite layers, the approach mitigates deleterious defects while enhancing crystallinity and charge carrier dynamics. Such control at the colloidal precursor level marks a paradigm shift in perovskite processing, offering a path toward commercial all-perovskite tandem cells that can consistently deliver high efficiency with long-term stability.

The implications of this work resonate through the broader field of optoelectronics and renewable energy. With theoretical efficiencies for all-perovskite tandem solar cells predicted to exceed 40%, strategies like those pioneered here are vital stepping stones to surpassing current photovoltaic technology thresholds. Moreover, the chemical insight gained through the interplay of tartrate and citrate anions, coupled with choline cation synergy, reveals a new dimension of colloid chemistry manipulation that may inspire innovations beyond photovoltaics, potentially touching other areas such as light-emitting diodes and photodetectors.

Financial support for this landmark study was provided by prominent Chinese national initiatives, including the National Key Research and Development Program, the Young Scientists Fund of the National Natural Science Foundation of China, and the National Natural Science Foundation of China. This backing underlines the strategic importance attributed to cutting-edge energy materials research in addressing global energy challenges.

In summary, the integrated colloidal chemistry approach to tuning nucleation kinetics in all-perovskite tandem solar cells embodies a significant technological leap. By resolving the crystallization mismatches that have historically hampered tandem device performance, the team’s work not only pushes conversion efficiencies near the 30% mark but also lays the foundation for stable, scalable, and commercially viable perovskite photovoltaics. This development signals a hopeful horizon for next-generation solar technology poised to deliver affordable, high-efficiency renewable energy worldwide.

Subject of Research: Not applicable
Article Title: Tailoring Colloidal Precursor Chemistry for Tunable Nucleation Kinetics in All-Perovskite Tandem Solar Cells​
News Publication Date: 27-Mar-2026
Web References: 10.1016/j.joule.2025.102381
References: Provided in the article DOI and journal publication
Image Credits: NIMTE

At the heart of this challenge is the complex chemistry and physics of multinary semiconductor materials like CZTSSe. Unlike simpler binary or ternary compounds, these materials consist of four or more elements whose interactions determine critical properties such as bandgap, carrier mobility, and defect formation. Consequently, the synthesis routes and formation pathways exert profound influence on the ultimate device performance. Recent advances have spotlighted the synthesis stage, particularly the design and use of molecular inks, as a pivotal aspect of kesterite fabrication that can unlock higher efficiencies.

Molecular inks are precursor solutions containing metal complexes and chalcogen sources that, upon deposition and thermal processing, form the kesterite thin film. This approach enables finer control over elemental distribution and uniformity at the nanoscale, which is indispensable for producing defect-minimized absorber layers. By tailoring the chemical state of these inks—through the choice of ligands, solvent environment, and precursor ratios—researchers can influence nucleation dynamics and crystallization pathways. This precise control mitigates the formation of detrimental point and extended defects, which historically limited photovoltaic performance by acting as recombination centers.

One of the notable breakthroughs reported in recent research is the crossing of the 15% efficiency threshold using molecular ink-based synthesis. This milestone signifies a critical step towards making kesterite solar cells viable competitors to established thin-film technologies like CdTe and CIGS. Achieving this level of performance required not only optimization of the ink chemistry but also a deep understanding of the post-deposition annealing and crystallization kinetics. Controlling these parameters allowed for the deliberate engineering of grain boundaries and the reduction of secondary phases, which often impair charge transport and extraction.

A central focus of the latest studies centers on defect chemistry in CZTSSe films. Unlike single-element semiconductors, multinary compounds are prone to complex defect configurations due to their multiple constituent atoms. The interplay between copper, zinc, tin, sulfur, and selenium can generate intrinsic defects that act as electron or hole traps. The molecular ink strategy aids in managing this complexity by ensuring homogeneous precursor mixing and facilitating optimal stoichiometry control. Such advancements directly translate to improved open-circuit voltage (Voc) and fill factor (FF) metrics in finished solar cells.

The synthesis temperature and atmosphere also play decisive roles in the quality of the kesterite absorber layers. High-temperature annealing under controlled environments promotes grain growth and defect passivation but can also risk the evaporation or segregation of volatile components. Fine-tuning these conditions in combination with molecular ink chemistry has allowed researchers to circumvent these drawbacks, preserving the desirable phase purity and enhancing device stability. Understanding these thermodynamic and kinetic processes at a granular level is vital for replicating laboratory successes at industry-relevant scales.

Furthermore, the use of molecular inks paves the way for low-cost, scalable fabrication techniques compatible with large-area substrates and roll-to-roll manufacturing. This aspect is critical for the commercial viability of kesterite photovoltaics, as it promises the reduction of material wastage and energy input during synthesis. Compared to vacuum-based deposition techniques common in other thin-film photovoltaics, ink-based methods present an attractive alternative that aligns with sustainable manufacturing goals.

The evolution of CZTSSe solar cells is also marked by the integration of sophisticated characterization tools that elucidate the material’s microstructure and electronic properties. Techniques such as time-resolved photoluminescence, scanning transmission electron microscopy, and X-ray diffraction mapping provide insights into defect distribution, phase segregation, and carrier dynamics. These analyses have been instrumental in refining molecular ink formulations and processing protocols, leading to solar cells with enhanced electron lifetimes and mobility.

Future directions in kesterite research, inspired by the molecular ink paradigm, include the exploration of novel ligands and solvent systems that further improve precursor solubility and stability. Some efforts are focused on incorporating additives that passivate defects or promote preferential crystallographic orientations to improve charge transport. Additionally, the development of multi-step annealing and selenization processes tailored to the ink chemistry offers pathways to engineer absorber layers with superior optoelectronic quality.

Moreover, understanding the fundamental thermodynamic principles governing the formation of secondary phases remains a critical research area. Unwanted phases such as ZnSe, Cu₂SnSe₃, or SnS can both consume active materials and create electronic barriers at interfaces. Molecular ink strategies enable dynamic compositional adjustments during synthesis, potentially minimizing these phases and optimizing absorber homogeneity. This fine balance between precursor chemistry and final film properties is key to pushing efficiencies beyond the current limits.

Beyond photovoltaic applications, the insights gained from the study of molecular ink chemistry and formation pathways in multinary semiconductors have broader implications. Similar methodologies could be applied to other emerging materials systems for optoelectronics, thermoelectrics, or photocatalysis. The foundational understanding of how precursor chemistry influences crystallization and defect landscapes could accelerate the discovery and optimization of materials with complex elemental compositions.

In conclusion, the breakthrough achievements in kesterite solar cells owe much to the meticulous control over precursor chemistry afforded by molecular inks. This synthesis pathway offers a robust platform for addressing the longstanding challenges in CZTSSe photovoltaic technology, including defect mitigation, phase purity, and large-scale manufacturability. As research continues to harness these advantages, the prospect of affordable, efficient, and environmentally benign solar energy conversion via kesterite cells appears increasingly within reach.

The path forward involves not only continued refinement of molecular ink formulations but also innovative device architectures and interface engineering to maximize power conversion efficiencies. Coupling these advances with computational modeling and machine learning could further accelerate the optimization process, tailoring synthesis parameters for custom applications. The confluence of chemistry, materials science, and engineering in this interdisciplinary effort is emblematic of the future of sustainable energy research.

Ultimately, the story of kesterite solar cells exemplifies how fundamental chemistry and careful materials design converge to solve complex technological challenges. As these solar cells edge closer to commercial viability, their success will represent a triumph of both scientific ingenuity and practical innovation, enabling a cleaner energy future powered by Earth-abundant materials.

Subject of Research: Synthesis and formation pathways of high-efficiency kesterite solar cells through molecular ink chemistry.

Article Title: Formation pathway of high-efficiency kesterite solar cells fabricated through molecular ink chemistry.

Article References:
Jimenez-Arguijo, A., Gong, Y., Caño, I. et al. Formation pathway of high-efficiency kesterite solar cells fabricated through molecular ink chemistry. Nat Energy (2026). https://doi.org/10.1038/s41560-025-01900-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-025-01900-y

A groundbreaking study now sheds new light on overcoming these challenges by introducing a novel surface-phase-transformation strategy employing a minimal incorporation of N-methyl pyrrolidone (NMP) into a piperazinium diiodide (PDI)-dissolved isopropanol solution. This innovative approach redefines the perovskite surface treatment protocol during the post-deposition stage, catalyzing a unique crystallization pathway. Unlike the conventional transition via a δ-intermediate phase to the α-phase perovskite, the addition of NMP directs the surface transformation through a solvated intermediate phase, which fundamentally alters the nucleation and growth dynamics at the atomic scale.

The emergence of this distinct crystallization mechanism not only elevates the crystallinity of the perovskite surface but also dramatically reduces interfacial contact losses. Crystallographic integrity is paramount to the optoelectronic behavior of PSCs; thus, the suppression of defects and grain boundary disorders at the interface directly mitigates pathways for non-radiative recombination. Enhanced surface crystallinity also contributes to an optimized energy band landscape, facilitating more efficient charge carrier extraction and transport.

Moreover, NMP’s presence enhances the molecular interaction between PDI and the perovskite layer. This reinforced chemical affinity at the interface seamlessly tunes the interfacial band alignment, thereby reducing energetic barriers that traditionally impede photogenerated charge carrier flow. The concerted effect of improved crystallinity and interface energetics manifests in a significant elevation of device performance metrics.

Empirical validation of this refined processing technique underscores its technological promise. The research reports certified power conversion efficiencies (PCEs) reaching an impressive 26.87% stabilized efficiency for single-junction PSCs. Beyond the lab-scale devices, the strategy has been successfully scaled to fabricate mini-modules achieving PCEs of 23.00%, alongside all-perovskite tandem devices that demonstrate record-setting efficiencies of 29.08%. These figures mark a new milestone in perovskite photovoltaic research, pushing the boundaries of what inverted PSC architectures can achieve.

Durability, often the Achilles’ heel of PSCs, is also critically addressed through this surface-phase-transformation strategy. Under continuous illumination at a standard 1-sun intensity and an elevated temperature of 65°C in ambient air, devices retained 96% of their initial efficiency over 2,500 hours. Such stability metrics signify a substantial leap forward in device longevity, aligning PSCs more closely with the practical requirements for commercial deployment and real-world operating conditions.

The mechanistic insights gleaned from this study underscore the intricate role of solvent-mediated intermediate phases in dictating perovskite lattice organization and surface morphology. By steering the crystal growth pathway away from the conventional δ-intermediate phase, the NMP involvement circumvents defect formation tendencies that act as non-radiative recombination centers. The solvated intermediates provide a dynamic, transient scaffold that promotes uniform crystallite expansion and reduces strain-induced defects—critical factors that traditionally undermine PSC efficiency and longevity.

Intriguingly, the enhanced PDI-perovskite interaction through NMP-facilitated molecular coordination exemplifies how subtle chemical modifications at interfaces can yield outsized effects. By improving electronic coupling and reducing trap densities, the interface acts not merely as a passive boundary but as an active participant in photovoltaic function. This paradigm reflects an evolving understanding that interface engineering holds the key to unlocking perovskite solar cell potential beyond material composition alone.

The scalability of this approach to mini-modules and tandem architectures illustrates its versatility and practical relevance. Tandem configurations, which stack multiple absorber layers to capture a broader solar spectrum, particularly benefit from intermediate band alignment optimization to minimize voltage losses and maximize current matching. The researchers’ ability to elevate tandem efficiency beyond 29% demonstrates the critical importance of controlled surface phase transformation in enabling complex device architectures.

From a materials science perspective, this work highlights the synergy between solvent chemistry, crystallography, and electronic structure engineering. The choice of NMP as a polar aprotic solvent fine-tunes the solvation environment during post-treatment, enabling tailored nucleation kinetics and defect passivation processes. This points to broader implications for solvent engineering as a versatile tool for controlling perovskite film quality and interfacial properties in diverse photovoltaic systems.

Looking forward, the implications for this surface-phase-transformation strategy extend beyond the immediate efficiency and stability benefits. The method could act as a benchmark for future perovskite interface modifications, inspiring the exploration of other chemically similar solvents and surface passivation agents. Such innovations might further push the efficiency envelope and enhance environmental robustness, propelling PSCs toward widespread commercial adoption.

Beyond technical achievements, the research contributes to the understanding of how dynamic intermediate phases influence photovoltaic performance, urging reexamination of established processing assumptions. It opens a new frontier in device engineering where transient chemical states are purposefully harnessed to steer crystallization and interface morphology, rather than solely being seen as processing artifacts. This reflects a maturation in perovskite research, emphasizing precision and predictability in fabrication protocols.

The environmental stability observed under operational conditions is particularly striking given the notorious sensitivity of perovskite materials to humidity, heat, and illumination. The improved contact and energy alignment reduce degradation pathways, suggesting that such chemical treatments may also protect perovskite layers from moisture ingress and ion migration. This could underpin the development of more resilient photovoltaic modules capable of withstanding the rigors of outdoor deployment.

In sum, the incorporation of NMP into the PDI-based post-treatment marks a pivotal advancement in perovskite solar cell manufacturing. It reveals how molecular-level modifications enacted through solvent chemistry can redefine crystal growth pathways and interface properties, culminating in unprecedented device performance and stability results. This study serves as a compelling blueprint for the next generation of photovoltaic research and technology development.

Such transformative improvements in PSCs promise to accelerate the penetration of solar photovoltaic technologies into the global energy landscape. The potential for highly efficient, durable, and cost-effective perovskite solar cells invigorates the vision of sustainable energy solutions capable of reducing carbon emissions and mitigating climate change. As research continues to refine these techniques, the prospect of scalable perovskite photovoltaics powering homes and industries worldwide draws ever closer to reality.

In conclusion, the solvated-intermediate-driven surface transformation strategy unveiled here offers a compelling synthesis of chemical ingenuity and materials science. By reimagining how perovskite surfaces evolve during post-treatment, the researchers dramatically elevate efficiency and operational stability, bringing perovskite solar technology closer to commercial viability. This milestone achievement encapsulates the vibrant trajectory of innovation defining the future of renewable energy technologies.

Subject of Research: Advanced surface engineering and interface optimization in lead halide perovskite solar cells

Article Title: Solvated-intermediate-driven surface transformation of lead halide perovskites

Article References:
Liu, S., Miao, T., Wang, J. et al. Solvated-intermediate-driven surface transformation of lead halide perovskites. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01912-8

DOI: https://doi.org/10.1038/s41560-025-01912-8