Perovskite solar cells have long dazzled laboratory audiences with efficiencies that keep climbing year after year, yet the technology has stubbornly struggled to translate those record numbers into large-area modules that can be manufactured reliably at scale. Now, a research team led by scientists at Nankai University in Tianjin, China, reports a solution to one of the most stubborn bottlenecks in the field: how to deposit a uniform, reactive nickel oxide hole-selective layer over large surfaces without sacrificing the electronic quality that makes small-area cells so spectacular. Writing in Nature Photonics, the team describes a coordination-regulated chemical bath deposition strategy that produces dense, conformal nickel oxide films, and uses them to demonstrate a certified power conversion efficiency of 27.35 percent in small-area inverted cells, along with module efficiencies of 23.42 percent on a 17.7-square-centimeter mini-module and 21.97 percent on an 81.5-square-centimeter module.
The importance of nickel oxide in inverted, or p-i-n, perovskite solar cells is difficult to overstate. In this architecture, the light-absorbing perovskite layer sits atop a hole-transporting layer, and every photon-generated hole must pass cleanly through that buried interface before it can be collected. Nickel oxide is prized for its chemical stability, wide bandgap, deep valence band and low cost, but depositing it uniformly over large areas has always involved a painful trade-off. Solution-based chemical bath deposition can cover large, even textured substrates conformally, but the rapid, disorderly hydrolysis of nickel salts tends to produce films riddled with pinholes and aggregates. Vacuum techniques such as sputtering or atomic layer deposition offer denser films but are slower, more expensive and harder to marry with high-throughput manufacturing.
The Nankai-led team attacked the problem at the level of crystallization kinetics rather than after the fact. Their insight was to introduce potassium tartrate, a ligand that binds nickel ions into exceptionally stable coordination complexes in the deposition bath. By sequestering a fraction of the free nickel ions, the ligand suppresses the chaotic, uncontrolled aggregation that normally plagues chemical bath growth and halves the hydrolysis rate constant, slowing it to 0.124 liters per mole per minute. That seemingly modest number is the heart of the result: slower, more orderly crystallization gives the film time to nucleate evenly across the substrate and to grow into a dense, continuous layer rather than a patchwork of islands and voids.
The kinetic control pays off in a striking way at the nanoscale. The resulting films are composed of remarkably refined crystallites measuring just 4.8 nanometers. For most materials, smaller grains would sound like a disadvantage, but here the fine nanostructure is precisely the point. Shrinking the crystallites maximizes the density of grain boundaries reaching the surface, and each boundary terminates in hydroxyl groups. These hydroxyl terminations serve as robust chemical anchoring sites for self-assembled monolayers, the carbazole-based phosphonic acid molecules that have become the workhorses of modern perovskite photovoltaics. A denser carpet of anchoring sites allows the monolayer to form a chemically cohesive, defect-suppressed buried interface, where charge extraction is fast and non-radiative recombination is minimized.
The team backed this picture with extensive interfacial characterization and charge-carrier dynamics measurements on nickel oxide monolayer stacks, supported by density functional theory calculations and molecular dynamics simulations that probed the coordination chemistry and the energetics of monolayer attachment. The calculations and experiments together paint a consistent story: the potassium tartrate-regulated surface is not merely smoother, it is chemically better matched to the self-assembled monolayer, so the molecules graft uniformly instead of clustering on reactive patches. Fewer clustered molecules means fewer shunting pathways and fewer deep traps, which translates directly into higher open-circuit voltage and fill factor.
The device numbers speak for themselves. Champion inverted cells built on the treated nickel oxide reached a power conversion efficiency of 27.40 percent, and an independent certified measurement returned a reverse-scan efficiency of 27.35 percent, placing these single-junction cells among the very best inverted devices ever reported. More importantly for commercialization, the advantage survived scale-up. A 17.7-square-centimeter mini-module achieved 23.42 percent efficiency, and a substantially larger 81.5-square-centimeter module still delivered 21.97 percent. In the perovskite field, where efficiency typically collapses as area grows because coating non-uniformities and interconnect losses compound, retaining better than 22 percent on a module the size of a postcard is a genuine milestone.
Efficiency alone, however, has never been the sole barrier to market entry. Stability under continuous illumination and heat has haunted perovskite devices since their inception, and the buried interface is one of the most common sites of degradation, where ion migration and interfacial reactions quietly erode performance. Here too the coordination-regulated films excelled. Small-area devices retained 90 percent of their initial efficiency after 2,656 hours of operation, and the 17.7-square-centimeter mini-modules held more than 90 percent of their initial performance after 1,200 hours under the demanding ISOS-L-1I protocol, an internationally recognized stress test combining continuous illumination with elevated temperature and electrical bias. Such endurance figures suggest that the defect-suppressed buried interface is not just a transient efficiency boost but a structural improvement in device physics.
What makes the result particularly compelling from a manufacturing standpoint is that the underlying technique is inherently scalable. Chemical bath deposition is a low-temperature, low-cost, solution-based process that requires no vacuum equipment and can, in principle, coat substrates of arbitrary size and shape, including textured surfaces that evaporative methods struggle to cover. By solving the coverage-versus-reactivity trade-off inside the bath chemistry itself, the researchers have essentially upgraded the method from a laboratory curiosity to a credible industrial candidate. The approach is compatible with subsequent self-assembled monolayer deposition and standard perovskite coating steps, meaning it slots into existing p-i-n fabrication flows without requiring an architectural rethink.
The work also carries a broader lesson for the field. Much of the recent progress in perovskite photovoltaics has come from interfacial engineering, and the Nankai study demonstrates that the substrate beneath a self-assembled monolayer is not a passive bystander but an active determinant of how well that monolayer performs. Controlling the crystallization kinetics of the inorganic layer, right down to the density of surface hydroxyl groups, is a form of interface design that operates one level deeper than most molecular engineering campaigns. It hints that similar coordination-regulated strategies could improve other metal oxide transport layers, from tin oxide electron contacts to zinc-based alternatives, across both single-junction and tandem devices.
Challenges remain before perovskite modules based on this chemistry can leave the laboratory for the factory floor. Scaling from 81.5 square centimeters to full-sized panels will require maintaining the same kinetic control across even larger baths and faster throughput, and long-term field testing beyond accelerated laboratory protocols will be essential. Lead content, encapsulation and recycling logistics also loom over the entire perovskite enterprise. But by demonstrating certified 27.35 percent cell efficiency, 23.42 percent module efficiency and more than a thousand hours of stable module operation from a single, industrially friendly deposition process, the team has decisively narrowed the gap between what perovskites can do in principle and what they can do in production. The sun delivers more energy to Earth in an hour than humanity uses in a year; chemistry like this brings the devices needed to harvest it one large step closer to being cheap, durable and genuinely scalable.
Subject of Research: Coordination-regulated chemical bath deposition of conformal nickel oxide hole-selective layers for efficient and stable perovskite solar modules
Article Title: Scalable and conformal nickel oxide for efficient perovskite solar modules
Article References: Yang, H., Wang, Y., Li, H., Wu, Y., Li, S., Han, X., Wang, D., Ding, Z., Han, Y., Zheng, Q., Chen, L., Du, Z., Alshahrani, T., Chen, C., Wang, X.-Y., Jiang, Y., & Yuan, M. (2026). Scalable and conformal nickel oxide for efficient perovskite solar modules. Nature Photonics. https://doi.org/10.1038/s41566-026-02012-z
Image Credits: AI Generated
DOI: 10.1038/s41566-026-02012-z
Keywords: perovskite solar cells, nickel oxide, chemical bath deposition, self-assembled monolayers, hole transport layer, power conversion efficiency, solar modules, crystallization kinetics, buried interface, photovoltaic stability, potassium tartrate coordination, ISOS-L-1I protocol
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Denise Maddox. (September 20, 2026). Nickel Oxide Breakthrough Pushes Perovskite Solar Modules Toward Commercial Reality. Scienmag. https://scienmag.com/nickel-oxide-breakthrough-pushes-perovskite-solar-modules-toward-commercial-reality/
Denise Maddox. “Nickel Oxide Breakthrough Pushes Perovskite Solar Modules Toward Commercial Reality.” Scienmag, 20 September 2026, https://scienmag.com/nickel-oxide-breakthrough-pushes-perovskite-solar-modules-toward-commercial-reality/. Accessed 20 September 2026.
Denise Maddox. “Nickel Oxide Breakthrough Pushes Perovskite Solar Modules Toward Commercial Reality.” Scienmag. September 20, 2026. https://scienmag.com/nickel-oxide-breakthrough-pushes-perovskite-solar-modules-toward-commercial-reality/
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Tags: advances in perovskiteburied interfacecertified power conversion efficiency in solar moduleschemical bath depositionchemical bath deposition for nickel oxidecrystallization kineticshole transport layerinverted (p-i-n) perovskite solar cell architectureISOS-L-1I protocollarge-area perovskite module manufacturingnickel oxidenickel oxide hole-selective layerperovskite solar cell commercialization challengesperovskite solar cell efficiencyPerovskite Solar Cellsphotovoltaic stabilitypotassium tartrate coordinationpower conversion efficiencyscalable perovskite module productionself-assembled monolayerssolar modulesstability and electronic quality of nickel oxide filmsthin-film deposition techniques for solar applicationstransparent conductive films in solar cells
