The solar cell industry has seen silicon maintain its position as the dominant technology for decades, mainly due to its well-established manufacturing infrastructure, proven reliability, and continuing cost reductions from economies of scale. However, silicon’s intrinsic properties impose limitations on cell thickness, weight, and flexibility, restricting their deployment in certain emerging applications such as wearable IoT devices, smart textiles, and mobile power solutions. This is where thin-film technologies come into play, offering ultra-thin, lightweight, and flexible alternatives that could complement silicon cells by covering usage niches where traditional modules fall short.

CIGS solar cells emerged as a promising thin-film technology in the late 20th century, partly driven by soaring silicon prices, which made alternative photovoltaics economically appealing. This compound semiconductor demonstrated impressive efficiency records achieved in laboratory environments—many of which were milestones at prominent research centers such as Empa. Substantial investments catalyzed company formations and large-scale product development globally. Nevertheless, the initial enthusiasm waned. Unlike silicon, CIGS manufacturing demands complex processes, including high-vacuum deposition techniques and precise compositional control, driving up production costs and complicating scale-up efforts. When silicon prices stabilized, the cost advantage diminished, and CIGS failed to penetrate the market as widely as envisioned.

Conversely, perovskite solar cells have witnessed an intense surge in research over approximately the last two decades. Named for their unique crystal structure, perovskites have revolutionized the photovoltaics landscape through their rapid efficiency gains and adaptable manufacturing techniques, such as solution processing and printing methods. These attributes potentially enable low-cost, high-throughput production. Globally, investments exceeded half a billion US dollars by 2025, signaling strong commercial interest. Empa itself has been at the spearhead of perovskite research and brought innovations to market through spin-offs like Perovskia Solar. Despite these advancements, perovskites face significant barriers—most notably, their chemical instability when exposed to moisture, oxygen, and thermal stress—limiting their operational lifetimes and real-world performance validation.

At the crux of progressing these technologies lies a fundamental insight: efficiency alone does not guarantee commercial success. While academia predominantly rewards breakthroughs in power conversion efficiency—high-impact publications and funding often follow efficiency records—the industry prioritizes factors essential for mass production and long-term viability. These include resilience against environmental degradation, manufacturing scalability, reproducibility of device performance, and sustainability considerations related to material sourcing and disposal. Mirjana Dimitrievska, the lead author of the study, emphasizes the importance of aligning research objectives with industrial demands such as extended operational lifetimes and cost-effective fabrication methods.

Another critical lesson distilled from the history of CIGS development is the value of collaboration and transparency between academia and industry. The study highlights instances where industrial partners dismissed certain research avenues based on proprietary, unpublished failure data—hindering academic groups from learning critical pitfalls and accelerating alternative approaches. Dimitrievska and colleagues advocate for sharing negative results and initiating collaborative efforts at earlier research stages to avoid redundant experimentation and expedite innovation cycles. This would not only avoid repeating costly mistakes but also tailor research outcomes more directly to industrial feasibility and market needs.

Research institutions like Empa play a pivotal role in this ecosystem by acting as conduits between fundamental research and industrial application. Unlike traditional universities, such institutes often have stronger linkages to industry and access to applied research funding programs like Innosuisse, which support targeted technology development. Leveraging these advantages can foster product-focused innovation that balances cutting-edge science with pragmatic constraints, propelling advances in both perovskite and CIGS photovoltaics toward commercial adoption.

Looking toward the future, the synergy between silicon and thin-film technologies offers an exciting pathway to dramatically enhance solar cell efficiency and functionality. Tandem cell architectures that stack a thin layer of perovskite or CIGS atop silicon exploit the complementary absorption spectra of these materials to surpass single-junction efficiency limits. Such hybrid approaches harness the maturity and reliability of silicon with the innovation and versatility of emerging films. The lightweight, flexible nature of thin-film layers expands the potential applications far beyond traditional rooftop solar installations, extending into flexible electronics, portable power sources, and autonomous sensor networks.

Although hurdles remain—particularly with the stability and long-term environmental robustness of perovskites—the rapid pace of global research aimed at overcoming these challenges fuels optimism. Parallel developments and renewed interest in CIGS technologies signal a renaissance for thin-film photovoltaics that could diversify the global solar energy portfolio. The continued influx of investments, combined with strategic partnerships bridging academic innovation and industrial pragmatism, sets the stage for these materials to realize their promise.

In summary, the trajectory of thin-film solar cell technologies underscores a vital paradigm: sustainable energy innovation demands more than breakthroughs in efficiency metrics. By integrating manufacturability, durability, and collaboration early in the development pipeline, researchers and industry can navigate complex commercial landscapes more effectively. As silicon reaches the limits of incremental improvement, the dawn of tandem and flexible solar cells shines brightly, heralding a new era where emerging semiconductors like CIGS and perovskites play transformative roles in powering a cleaner, more adaptable energy future.

Subject of Research: Not applicable

Article Title: Lessons from copper indium gallium sulfo-selenide solar cells for progressing perovskite photovoltaics

News Publication Date: 16-Jan-2026

Web References:
10.1038/s41560-025-01936-0

Image Credits: Empa

Keywords: Solar cells, thin-film photovoltaics, perovskite solar cells, CIGS, tandem solar cells, photovoltaic efficiency, renewable energy, flexible solar technology, commercialization challenges, material stability, photovoltaic manufacturing, sustainable energy

Electron-transport layers crafted with SnO₂ via CBD serve as critical mediators in efficiently extracting and transporting electrons generated in the perovskite absorber layer. Central to achieving high device performance is the formation of ETLs exhibiting uniform morphologies, minimal defect densities, and robust interfacial properties. The conventional CBD synthesis of SnO₂ typically proceeds via two competing nucleation pathways: cluster-by-cluster aggregation and ion-by-ion growth. Unfortunately, the cluster-by-cluster pathway often dominates, leading to heterogeneous deposition characterized by incomplete surface coverage and the formation of defects detrimental to charge transport and recombination dynamics.

The novel approach employs an excess ligand environment that fundamentally alters the deposition kinetics, effectively suppressing the cluster-by-cluster mechanism while preferentially facilitating the ion-by-ion growth pathway. This strategic modulation of growth dynamics enables the formation of highly uniform, conformal SnO₂ thin films, even on large substrates, within markedly reduced synthesis times. The resulting films exhibit substantially suppressed defect densities, manifesting superior optoelectronic properties necessary for high-performance solar devices.

A pivotal metric reflecting the quality of these SnO₂ films is the surface recombination velocity, which is critically lowered to 5.5 cm s⁻¹ in this work. The surface recombination velocity quantifies the propensity for photogenerated carriers to recombine at interfaces before contributing to photocurrent. Lowering this parameter illustrates the efficacy of the excess ligand strategy in passivating surface states and minimizing trap-assisted recombination, an achievement rarely realized with conventional CBD films.

Moreover, the luminescent properties of these SnO₂ films set new benchmarks in the realm of perovskite photovoltaics. Exhibiting an electroluminescence efficiency of 24.8%, these ETLs contribute not only to improved charge extraction but also function effectively as recombination suppression layers, which is vital for device stability and long-term operational performance. This high electroluminescence yield reflects a pronounced reduction of non-radiative recombination pathways, underscoring the quality of the interface engineered via this method.

The impact of these advanced SnO₂ ETLs permeates through the entire solar cell architecture, culminating in impressive photovoltaic efficiencies. The study reports a power-conversion efficiency (PCE) of 26.4% for champion perovskite solar cells, which aligns with or surpasses state-of-the-art figures. Such efficiencies herald the maturity of the excess ligand CBD method as a scalable technique capable of supporting commercial-level device fabrication.

Extending beyond individual cells, the practical scalability of this technique is demonstrated by achieving a 23% efficiency in perovskite solar modules, devices that integrate multiple cells to deliver higher voltage and practical power outputs suitable for real-world applications. Furthermore, the method’s compatibility with carbon-based perovskite cells yielding an efficiency of 23.1% showcases its versatility and adaptability to diverse device architectures, broadening the potential market impact.

Technically, the suppression of the cluster aggregation path involves the deliberate introduction of ligand molecules in excess relative to conventional protocols. These ligands coordinate with tin ions, stabilizing them and moderating nucleation kinetics. This molecular-level control steers the growth preferentially towards direct ion-by-ion deposition onto the substrate, circumventing the formation of colloidal SnO₂ clusters that compromise film integrity.

Such ligand-rich environments also provide biochemical passivation of surface defects, which act as recombination centers in the final film. By saturating these sites during growth, the excess ligand method mitigates mid-gap states and traps that traditionally plague ETLs derived from wet chemical methods. Consequently, charge carriers experience smoother transit through the ETL, enhancing open-circuit voltage and fill factor metrics in the integrated devices.

The rapidity of this deposition approach marks an additional industrial advantage. Conventional CBD techniques require extended durations to achieve coverage uniformity, a major bottleneck when moving toward manufacturing scale. By shifting the reaction pathway kinetics, the excess ligand strategy compresses processing times without sacrificing film quality or uniformity. This reduction in synthesis time translates directly to cost savings and higher throughput in manufacturing environments.

Importantly, the framework of this study also tackles oxidation-related degradation issues. In traditional solution-processed SnO₂ films, uncontrolled oxidative growth can induce variable stoichiometries and localized defects. The controlled ligand environment buffers the chemical milieu, leading to stoichiometrically consistent, phase-pure SnO₂ layers with improved chemical robustness, an essential factor for device longevity.

This research not only bridges the gap between laboratory-scale device fabrication and industrially feasible production but also enhances our fundamental understanding of nucleation dynamics in chemical bath depositions. The manipulation of ligand content as a lever to control nucleation pathways opens avenues for similarly structured approaches in other oxide semiconductors, potentially revolutionizing the fabrication of electron-transport layers beyond SnO₂.

The implications extend into the broader context of perovskite photovoltaics, where enhancing interface quality is crucial for overcoming stability and efficiency bottlenecks. Defect suppression at the ETL/perovskite interface reduces hysteresis phenomena and photodegradation pathways, two persistent challenges inhibiting broader adoption of perovskite solar technology. By addressing these through material synthesis innovation, the study brings the community closer to realizing commercially viable perovskite modules.

Looking forward, integrating the excess ligand CBD method with roll-to-roll processing and other scalable deposition techniques posits a promising route toward flexible, lightweight solar modules with low manufacturing costs. The combination of superior performance metrics and scalable fabrication processes could accelerate the deployment of perovskite-based photovoltaics in large-scale energy projects.

In conclusion, the discovery of an excess ligand strategy in the chemical bath deposition of SnO₂ represents a paradigm shift in fabricating electron-transport layers for perovskite solar cells. By tailoring nucleation pathways to prioritize ion-by-ion growth over cluster aggregation, researchers have achieved uniform, defect-minimized films with exceptional optoelectronic attributes. This advancement translates directly into record-setting device efficiencies and scalable production capabilities, fostering new possibilities in the sustainable energy industry. As the photovoltaic sector intensifies its quest for superior materials and processes, this work stands poised to inspire future innovations that bridge the divide between research breakthroughs and real-world applications.

Subject of Research: Electron-transport layers in perovskite solar cells; chemical bath deposition of tin oxide.

Article Title: Efficient and luminescent perovskite solar cells using defect-suppressed SnO₂ via excess ligand strategy.

Article References:
Seo, G., Yoo, J.J., Nam, S. et al. Efficient and luminescent perovskite solar cells using defect-suppressed SnO₂ via excess ligand strategy. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01781-1

Image Credits: AI Generated

Wide-bandgap perovskites, especially all-inorganic compositions such as cesium lead iodide bromide (CsPbI₂Br), are prized for their suitability as top-cell materials in tandem solar cells. Their larger bandgaps improve photovoltage and tandem efficiency, yet their practical implementation is vexed by issues including uncontrolled crystallization processes, abundant defect states, energetic misalignment at interfaces, and phase instability. These problems tend to originate predominantly at the critical interface where the perovskite layer contacts the underlying electron transport layer, frequently a tin oxide-based material.

Tin oxide (SnO₂) has emerged as a popular electron transport layer due to its optical transparency, high electron mobility, and thermal stability. However, when utilized in its conventional alkaline-based solution-processed form, SnO₂ often induces deleterious effects to the overlying perovskite film. The alkaline environment disrupts stoichiometry and crystallization dynamics, promoting defect formation and undesirable phase transformations. These interfacial imperfections exacerbate non-radiative recombination and voltage losses, ultimately dampening device performance and operational durability.

To overcome these hurdles, the authors crafted an innovative bottom interface modulation approach by synthesizing acidic magnesium-doped tin oxide quantum dots. This acidic nanomaterial sculpted a more benign and optimized contact surface conducive to the nucleation and growth of high-quality CsPbI₂Br thin films. Unlike traditional alkaline SnO₂, this magnesium-doped variant delicately balances the physical, chemical, structural, and energetic properties of the interface. This synergy results in profound passivation of trap states, significantly reducing carrier recombination pathways.

The magnesium doping not only adjusts the acidity of the quantum dot dispersion but concurrently fine-tunes the energy band alignment between the electron transport layer and the wide-bandgap perovskite. This precise energetic matching facilitates efficient electron extraction and minimizes energy losses at the interface. Furthermore, the controlled acidic environment promotes uniform perovskite film morphology with larger grain sizes and fewer pinholes, key factors that support enhanced charge transport and suppression of defect proliferation.

Delving deeper into the instability mechanisms previously encountered with alkaline-based tin oxide contacts, the study reveals that the basic nature of the conventional SnO₂ solution provokes deleterious chemical interactions at the interface. These reactions destabilize the CsPbI₂Br lattice and trigger phase transitions that deteriorate device longevity. By contrast, the acidic magnesium-doped SnO₂ quantum dots not only foster superior initial film quality but also fortify the structural integrity against environmental and operational stresses.

Performance metrics cement the remarkable improvements afforded by this bottom contact engineering innovation. The standalone wide-bandgap CsPbI₂Br perovskite solar cell achieves a striking power conversion efficiency of 19.2% alongside a high open-circuit voltage (V_oc) of 1.44 V, exemplifying substantial reduction in voltage losses. This milestone embodies a significant leap over prior records hampered by interfacial defects and instability.

Extending this advancement to the tandem format, the researchers seamlessly integrated the improved inorganic top cell with an optimized organic bottom cell, yielding a monolithic perovskite/organic tandem solar cell exhibiting an impressive efficiency of 25.9%, certified at 25.1%. This achievement ranks among the highest certified efficiencies reported for perovskite-based tandems and signals a promising future for these hybrid photovoltaic platforms.

Beyond sheer efficiency, the tandem device manifests enhanced long-term stability under diverse environmental conditions, spanning thermal, humid, and illumination stress tests. Such robustness is critical for transitioning laboratory innovations into real-world applications, where operational durability remains a primary concern.

The authors’ work exemplifies the transformative impact of interface chemistry and nanoscale material engineering on next-generation photovoltaic technologies. By challenging conventional electron transport layer paradigms and introducing a finely tuned acidic magnesium-doped SnO₂ quantum dot system, the research community gains a potent toolkit to tackle persistent instability and performance bottlenecks inherent to wide-bandgap perovskite devices.

This bottom contact modulation strategy not only signals a promising route to push power conversion efficiencies closer to their theoretical maxima but also invigorates tandem solar cell architectures with the stability and performance reliability necessary for commercialization. Given the ongoing quest for cost-effective, high-efficiency solar energy conversion, these findings resonate broadly across academia and industry, attracting attention from materials scientists, chemists, and photovoltaic engineers alike.

Moreover, the study provides a compelling mechanistic framework elucidating how subtle shifts in solution pH and quantum dot doping radically alter interfacial interactions, crystallization kinetics, and energetic alignments. Such insights will undoubtedly spur further exploration into tailored interface materials and nanoscale design strategies to address analogous challenges in other optoelectronic devices.

In summary, the research by Han et al. delivers an elegant and effective solution to one of the most pressing challenges in wide-bandgap perovskite solar cells. The use of acidic magnesium-doped SnO₂ quantum dots as a bottom contact modulator achieves a harmonious balance of chemical compatibility, structural optimization, and energy band alignment. This balance yields perovskite films with reduced defects, enhanced stability, and superior photovoltaic performance.

The resultant high-efficiency tandem device, combining the merits of inorganic perovskites with organic photovoltaics, underscores the versatile potential of hybrid architectures. As the solar industry strives for sustainable, efficient energy solutions, such scientific breakthroughs offer compelling pathways toward scalable, durable, and high-performing solar cells.

Looking ahead, the interface engineering paradigm illustrated here opens avenues for integrating other dopants and fine-tuning interface acidity/basicity to engineer bespoke electron transport layers tailored for diverse perovskite and tandem compositions. This flexible approach promises to accelerate the development of commercial-grade solar cells capable of meeting global energy demands with improved cost-effectiveness and reliability.

In essence, this study not only advances the state-of-the-art of perovskite and tandem photovoltaics but also enriches our fundamental understanding of interfacial chemistry in complex optoelectronic systems. The successful implementation of this bottom contact modulation strategy represents a major stride toward realizing the full potential of wide-bandgap perovskites in next-generation solar energy technologies.

Subject of Research: Interface engineering in wide-bandgap cesium lead halide perovskite solar cells and perovskite/organic tandem photovoltaics.

Article Title: Inorganic perovskite/organic tandem solar cells with 25.1% certified efficiency via bottom contact modulation.

Article References:
Han, Y., Fu, J., Ren, Z. et al. Inorganic perovskite/organic tandem solar cells with 25.1% certified efficiency via bottom contact modulation. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01742-8

Image Credits: AI Generated