The new illumination-assisted annealing process represents a paradigm shift by enabling photo-induced crystallization of Se films at ambient temperatures, effectively suppressing the detrimental dewetting phenomenon that previously limited film quality. By initially irradiating the selenium film under carefully controlled light exposure, the researchers facilitate the growth of substantially larger crystalline grains, achieving an average grain size of approximately 2.7 μm—over five times larger than conventional films. This enhancement in grain structure translates directly into fewer trap states where charge carriers could recombine non-radiatively, a chief mechanism that undercuts cell efficiency.

Following this photo-induced crystallization, the films undergo a subsequent thermal annealing step to consolidate their enhanced microstructural and electronic properties. The collaborative effect of these sequential processes results in selenium films with remarkably reduced trap-state density, measured to be on the order of 6.9 × 10¹⁴ cm⁻³, and notably extended carrier lifetimes reaching 22.9 nanoseconds. These metrics signify a substantial reduction in recombination centers and improved charge transport, both critical factors in lifting the limiting efficiency barriers that have stalled selenium photovoltaics for decades.

Harnessing these advanced films, the research team has demonstrated certified power conversion efficiencies in selenium solar cells exceeding 10%, with a record-setting open-circuit voltage of 1.03 V. This represents a historic milestone for Se photovoltaics, positioning them competitively not only as candidates for tandem solar cells but also in emerging applications under indoor light environments where wide bandgap materials excel. The open-circuit voltage figure is particularly noteworthy as it surpasses 1 volt, an indicator of photovoltaic quality previously unattainable for selenium-based devices.

Additionally, the durability of the fabricated selenium solar cells is equally impressive. Under rigorous operational conditions—sustained maximum power point tracking for 1,000 hours in ambient air without any encapsulation—the devices showed negligible performance degradation. This robustness highlights selenium’s intrinsic material stability advantage, promising long-term reliability and cost-effective deployment in real-world environments where encapsulation can add complexity and expense.

The illumination-assisted crystallization technique addresses one of the long-standing material synthesis challenges in selenium photovoltaics. Conventional thermal annealing methods often promote rapid dewetting of selenium films, resulting in discontinuous, polycrystalline layers with defective interfaces and small grain sizes. By contrast, light irradiation triggers localized heating and photo-chemical effects while maintaining a controlled ambient temperature, allowing selenium atoms to rearrange into larger, well-oriented crystalline domains. This nuanced control over the microstructure is what underlies the substantial improvements in electronic properties and device performance.

This breakthrough holds particularly exciting implications for tandem solar cells, where wide bandgap absorbers are employed to capture the high-energy portion of the solar spectrum while lower bandgap materials capture the remainder, maximizing the overall efficiency beyond single-junction limits. Selenium’s bandgap near 1.9 eV matches the ideal top-cell absorber bandgap that can be paired with silicon or other narrow-gap materials in tandem architectures. With this renewed processing approach, selenium’s historical photovoltaic legacy is revitalized with cutting-edge performance metrics suitable for modern sustainable energy solutions.

The researchers also highlight selenium’s potential in indoor photovoltaic applications, where illumination conditions differ significantly from sunlight. The wide bandgap and high open-circuit voltage enable selenium cells to operate efficiently under artificial light sources, expanding their utility in powering low-consumption electronics, Internet of Things (IoT) devices, and other ambient-light energy harvesting scenarios. The film stability and low trap density evident under these ambient conditions underscore selenium’s versatility as a solar material adaptable to diverse technological needs.

Scientifically, this work reveals new fundamental insights into crystallization dynamics under photo-assisted annealing conditions. The interplay between photon-induced atomic mobility and minimal thermal input fosters a unique material evolution pathway unprecedented in conventional semiconductor manufacturing. This discovery paves the way for further exploration of light-assisted processing in other semiconductor systems, which may yield similarly transformative material and device advancements.

Beyond efficiency gains, the simplicity and scalability of the illumination-assisted annealing technique also bear significant technological promise. The ambient temperature crystallization step reduces energy input requirements compared to high-temperature processes, making it more environmentally friendly and cost-effective. These attributes satisfy critical criteria for industrial viability, potentially facilitating the widespread commercial adoption of selenium-based photovoltaics, which have historically faced integration challenges despite selenium’s advantageous optoelectronic properties.

In summary, this research heralds a new era for selenium photovoltaics by merging time-honored material qualities with innovative light-driven processing techniques. By surpassing the 10% efficiency threshold and delivering a high open-circuit voltage alongside enduring device stability, selenium is repositioned from an early photovoltaic relic to a state-of-the-art contender. This advancement promises to enrich the portfolio of wide bandgap materials accessible for next-generation solar energy harvesting, offering pathways to both enhanced performance tandem configurations and resilient indoor power sources.

As the global race to harness renewable energy intensifies, breakthroughs like this underscore the value of revisiting and revitalizing classic materials with modern scientific ingenuity. Selenium’s transformation through illumination-assisted annealing demonstrates that old photovoltaic champions still have untapped potential to shape the future landscape of sustainable energy technology.

The implications for the photovoltaic industry are profound, as improving cell efficiency while reducing processing temperatures and costs aligns with market demands for competitive, scalable solutions. Moreover, the long-term stability shown by these selenium solar cells under ambient conditions bodes well for their deployment in diverse environmental settings, from urban rooftops to remote indoor applications.

Future research directions spurred by these findings may include detailed exploration of the photo-induced crystallization mechanism at atomic scales, optimization of annealing parameters for maximum grain size control, and integration of selenium films into tandem devices with complementary absorbers. Researchers may also investigate encapsulation strategies tailored to selenium’s unique chemistry to extend operational lifetimes even further.

This novel annealing strategy revitalizes selenium’s photovoltaic prospects by harnessing the synergistic effects of light and heat, setting a new benchmark in the field. The seamless combination of fundamental material science with innovative process engineering exemplifies how interdisciplinary approaches continue to drive solar cell technologies toward ever higher efficiencies, sustainability, and commercial viability.

With certified efficiencies exceeding 10% and a robust open-circuit voltage above 1 V, selenium solar cells leap into practical relevance for the first time in decades. As the sunlight-harvesting power of this ancient semiconductor is rekindled via illumination-assisted annealing, the door opens for new photovoltaic architectures and applications that could accelerate the global transition to clean energy.

Subject of Research: Selenium solar cells and photo-assisted annealing techniques for efficiency and stability enhancement.

Article Title: Illumination-assisted annealing enables selenium solar cells with open-circuit voltage over 1 V and efficiency exceeding 10%.

Article References: Wen, X., Li, Z., Lu, W. et al. Illumination-assisted annealing enables selenium solar cells with open-circuit voltage over 1 V and efficiency exceeding 10%. Nat Energy (2026). https://doi.org/10.1038/s41560-025-01939-x

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-025-01939-x

Keywords: Selenium photovoltaics, illumination-assisted annealing, photo-induced crystallization, wide bandgap solar cells, tandem solar cells, indoor photovoltaics, power conversion efficiency, open-circuit voltage, carrier lifetime, trap state density, solar cell stability

In an important breakthrough, researchers have unveiled a novel dipolar passivation strategy that not only mitigates interfacial trap states but also precisely tailors the energy level alignment at the HTL/perovskite junction. This dual-function approach radically transforms the interface by simultaneously enhancing charge extraction and reducing unwanted recombination. By doing so, it opens new avenues for improving the efficiency and stability of lead-tin (Pb-Sn) based narrow-bandgap perovskite solar cells, which are integral for high-efficiency all-perovskite tandem devices.

The challenge of minimizing non-radiative recombination losses at the HTL/perovskite interface has long been magnified in lead-tin mixed perovskites. Conventional passivation approaches predominantly rely on long-chain amine molecules that introduce insulating layers, impeding charge transport. While these methods reduce trap states, they unintentionally compromise both the fill factor (FF) and the short-circuit current density (J_sc), fundamentally limiting the output power and efficiency of the cell. The delicate balance between effective passivation and efficient charge extraction has remained elusive—until now.

The new dipolar passivation method leverages molecular dipoles to engineer the electrostatic landscape at the interface. By depositing a thin, dipolar layer, the researchers induced a favorable energy level alignment that facilitates ohmic contact between the perovskite and the HTL. This configuration markedly improves hole injection efficiency while simultaneously repelling electrons, thereby suppressing recombination at the interface. Such precise control over interfacial energy levels exemplifies a sophisticated yet pragmatic strategy to overcome long-standing material limitations.

One of the remarkable consequences of this passivation strategy is the dramatic extension of the carrier diffusion length within the Pb-Sn perovskite layer, reaching an impressive 6.2 micrometers. This enhancement is critical because longer diffusion lengths enable photo-generated carriers to traverse the perovskite absorber without recombining prematurely, thereby maximizing current extraction and device efficiency. By ensuring that more charge carriers contribute to the electrical output, the strategy effectively elevates device performance metrics on multiple fronts.

Performance-wise, the impact of the dipolar passivation approach has been significant. Pb-Sn perovskite single-junction devices treated with this strategy achieved a power-conversion efficiency of 24.9%, with an open-circuit voltage (V_oc) of 0.911 V—a noteworthy improvement considering the traditionally challenging nature of Pb-Sn perovskites. Additionally, these devices exhibited a high short-circuit current density (33.1 mA/cm^2) and an excellent fill factor of 82.6%, parameters that underscore the superior charge collection dynamics enabled by the passivated interface.

Beyond single-junction devices, the dipolar passivation technique holds profound implications for all-perovskite tandem solar cells. The researchers demonstrated that passivation effectively mitigates contact losses frequently induced by the interconnecting layers that bridge the wide-bandgap and narrow-bandgap subcells. These interfacial modifications translate into tandem devices that exhibit remarkable power-conversion efficiencies, reaching 30.6% under standard test conditions, with stabilized efficiencies certified at 30.1%.

This efficiency milestone positions all-perovskite tandem solar cells as highly competitive candidates for next-generation photovoltaics, surpassing many incumbent technologies in both performance and material sustainability. The findings not only offer a solution to interfacial recombination but also showcase how molecular engineering at buried interfaces can unlock substantial gains in device performance without compromising stability or manufacturability.

The interdisciplinary nature of this research—merging molecular chemistry, materials science, and device engineering—highlights the importance of interface science in renewable energy innovation. It opens a new chapter in perovskite solar cell research, where precise interfacial control is as critical as the bulk optoelectronic properties of the absorber materials themselves. These advances may accelerate the commercialization timeline of all-perovskite tandem photovoltaics, potentially reducing costs and boosting adoption worldwide.

Furthermore, considering the scalability of the dipolar passivation process, its integration into existing perovskite device fabrication protocols appears feasible. This adaptability is crucial for transitioning laboratory-scale breakthroughs into industrial-scale manufacturing, thereby facilitating the deployment of high-efficiency tandem modules in real-world solar installations.

The reported outcomes stem from meticulous experimentation combined with sophisticated characterization techniques to unravel and optimize the molecular dipole effects at the buried interface. These efforts underscore the importance of fundamental understanding in interface phenomena, emphasizing that future enhancements will likely continue to arise from smart chemical and physical passivation schemes.

As the photovoltaic community pushes towards the elusive 35% efficiency target for tandem solar cells, the insights from this dipolar passivation research provide a clear pathway. By addressing one of the most stubborn losses in narrow-bandgap subcells, this approach paves the way for perovskite tandems to achieve efficiencies previously thought to be out of reach, heralding a new era of solar energy harvesting that is both efficient and scalable.

In conclusion, the innovative dipolar passivation method introduced offers a transformative strategy for tackling interface-related recombination losses in Pb-Sn perovskite solar cells. Its profound impact on charge carrier dynamics, energy level alignment, and overall device performance represents a significant leap forward in the perovskite photovoltaic field. This breakthrough not only advances the fundamental understanding of buried interface physics but also brings the vision of high-efficiency, all-perovskite tandem solar technology closer to reality.

Subject of Research: Development of dipolar passivation strategies to reduce non-radiative recombination and improve efficiency in lead-tin narrow-bandgap perovskite solar cells and all-perovskite tandem solar cells.

Article Title: All-perovskite tandem solar cells with dipolar passivation.

Article References:
Lin, R., Gao, H., Lou, J. et al. All-perovskite tandem solar cells with dipolar passivation. Nature (2025). https://doi.org/10.1038/s41586-025-09773-7

Image Credits: AI Generated