CIGS solar cells emerged from decades of rigorous scientific exploration and engineering refinement. Their attributes, including a favorable bandgap, high absorption coefficient, and mechanical flexibility, positioned them as promising candidates for lightweight, versatile solar modules. Despite achieving considerable efficiency milestones, CIGS struggled in large-scale manufacturing environments. The challenges were multifaceted, encompassing difficulties in maintaining material uniformity, complex deposition techniques, and the intricate interplay between materials chemistry and device architecture. These obstacles contributed to a delay in commercial adoption, emphasizing the necessity of aligning materials research with scalable production strategies.

On the other side of the spectrum, metal halide perovskite solar cells have garnered intense interest for their rapid climb in efficiency, outpacing many established photovoltaics shortly after inception. This meteoric rise, however, has been shadowed by concerns regarding stability, manufacturability, and integration into existing industrial frameworks. Perovskites are particularly vulnerable to environmental factors such as moisture, heat, and ultraviolet light, which can trigger degradation pathways, undermining device longevity. Researchers are actively developing novel compositional engineering and encapsulation techniques to enhance durability, learning from the hard-earned experiences recorded by their thin-film predecessors.

The comparative analysis of CIGS and perovskites underscores the critical need for holistic approaches in thin-film PV development. CIGS’s journey vividly illustrates how interdependence among materials properties, device design decisions, and manufacturing methodologies can make or break the transition from laboratory innovation to commercial success. For perovskites, a similar synchronization must be established early on. Innovations in material chemistry must be paired seamlessly with scalable fabrication processes that preserve efficiency while ensuring long-term stability in real-world conditions.

One striking aspect of the CIGS experience was the complexity of its deposition processes, such as co-evaporation and sputtering, which demanded exceedingly precise control over elemental ratios and growth conditions. These meticulous requirements often limited throughput and elevated production costs, hindering widespread deployment. For perovskite solar cells to evade such pitfalls, researchers are pioneering solution processing and low-temperature fabrication methods that promise compatibility with large-area manufacturing and flexible substrates. However, the trade-off between simplicity of processing and device performance remains a delicate balance to strike.

Long-term operational stability emerged as a fundamental challenge for both technologies, albeit manifested differently. While CIGS devices exhibited commendable lifetimes under various stress tests, the path to such robustness was iterative and arduous. Perovskites, with their inherently unstable crystal lattice subjected to ionic migration and photochemical reactions, demand innovative strategies to suppress intrinsic degradation mechanisms. Multilayer passivation, compositional tuning, and interface engineering are among the advanced techniques being deployed to curtail the vulnerabilities of perovskite absorbers and charge transport layers.

In addition to material and device considerations, the scale-up of fabrication presents systemic challenges that CIGS solar cells also faced. The conversion from small-scale laboratory cells to modules capable of end-use power generation exposed issues such as uniform layer deposition over large areas, maintaining interface integrity, and ensuring reproducibility. Recognizing these challenges early on allowed CIGS developers to refine production equipment and optimize workflows, though not without substantial time and investment. This experience sends a clear message to perovskite researchers: industrial feasibility must be a co-equal focus alongside performance metrics.

Environmental and economic factors also weigh heavily on the future viability of thin-film photovoltaics. The sustainability footprint of complex manufacturing techniques, the availability and toxicity of precursor materials, and lifecycle considerations form an integral part of commercialization pathways. CIGS technologies had to navigate concerns regarding the use of rare elements like indium and gallium, as well as selenium compounds. Perovskites, while benefiting from more abundant constituents, still face scrutiny over lead content and recycling protocols, necessitating parallel research on lead-free formulations and environmentally responsible disposal methods.

The ongoing dialogue between historical thin-film technologies and emergent materials like perovskites offers fertile ground for interdisciplinary innovation. By dissecting the myriad factors that governed CIGS solar cell development, researchers can formulate strategies that anticipate and preempt challenges in perovskite research. This includes early adoption of robust testing standards, collaborative engagement between academia and industry, and system-level thinking that covers every stage from material synthesis to module deployment.

Moreover, the narrative of CIGS highlights the importance of aligning policy frameworks and market incentives with technological advancements. Despite promising laboratory results, commercial uptake requires a conducive ecosystem where incentives for investment, standardization of certification, and infrastructure for mass production converge. Perovskite photovoltaics, with their unique opportunities and vulnerabilities, will benefit immensely from such integrated approaches that blend science, engineering, and policy into coherent development roadmaps.

The lesson is clear: innovation in photovoltaic technology must transcend incremental improvements and embrace a systemic perspective that integrates performance, stability, manufacturability, and economic viability from inception. The remarkable strides of perovskites are encouraging but incomplete without addressing these intertwined facets. Drawing upon the CIGS experience, researchers and industry stakeholders are encouraged to synchronize efforts, fostering a collaborative environment where advances in one domain support progress in others.

In conclusion, the historical wisdom embedded in the evolution of CIGS solar cells provides an invaluable template for guiding perovskite photovoltaics toward sustainable, scalable, and impactful implementation. By learning from past successes and obstacles, the photovoltaic community is better equipped to forge a deliberate path, minimizing avoidable risks and accelerating the realization of flexible, efficient, and durable solar technologies. The future of perovskites, therefore, hinges not just on the breakthroughs yet to come but on a reflective understanding of lessons already learned.

As the global demand for renewable energy escalates, the imperative to develop PV technologies that are not only high-performing but also adaptable and economically viable becomes undeniable. The juxtaposition of CIGS and perovskite research trajectories serves as a beacon, illuminating the multifaceted challenges ahead and inspiring a synergistic approach that capitalizes on past insights to innovate responsibly. The convergence of material science, engineering ingenuity, and industrial pragmatism heralds a promising era for thin-film photovoltaics that could transform the energy landscape.

Ultimately, the success of perovskite solar cells will depend on the community’s ability to synthesize scientific curiosity with pragmatic strategies, fostering technologies ready to meet the complex demands of a sustainable future. Reflecting on the CIGS experience equips the field with the contextual awareness necessary to avoid repeating missteps while championing innovations that can redefine how we harvest the sun’s energy.

Subject of Research:
Lessons from copper indium gallium sulfo-selenide (CIGS) solar cells to advance perovskite photovoltaics.

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

Article References:
Dimitrievska, M., Saucedo, E., De Wolf, S. et al. Lessons from copper indium gallium sulfo-selenide solar cells for progressing perovskite photovoltaics. Nat Energy (2026). https://doi.org/10.1038/s41560-025-01936-0

Image Credits:
AI Generated

DOI:
https://doi.org/10.1038/s41560-025-01936-0

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