In the relentless pursuit of advancing solar energy technology, thin-film tandem solar cells have emerged as one of the most promising avenues for achieving high-efficiency, lightweight, and cost-effective photovoltaic devices. Among the various material combinations explored, the integration of wide-bandgap perovskites with Cu(In,Ga)Se₂ (CIGS) absorbers is rapidly gaining attention due to their complementary absorption spectra and potential for enhanced power conversion efficiencies (PCE). However, despite significant progress, these tandem architectures have yet to reach the performance and stability levels demonstrated by their single-junction counterparts. A core challenge lies in mitigating recombination losses and managing photothermal-induced degradation within the wide-bandgap perovskite layers. Addressing these hurdles is paramount to unlocking the full potential of perovskite/CIGS tandem solar cells.
Recent research spearheaded by Pei, Lin, Zhang, and colleagues has brought to light a fundamental bottleneck in the reliability of defect passivation strategies applied to wide-bandgap perovskites. Passivation—crucial for suppressing non-radiative recombination and enhancing photovoltaic efficiency—often falters under operational stresses combining illumination and elevated temperatures. The root cause identified in this comprehensive study is the thermal desorption of conventional passivating agents from the perovskite surface, which leads to the resurgence of detrimental defects and accelerated device degradation. This revelation challenges the current paradigm and underscores the necessity of rethinking molecular designs of passivators to withstand real-world stresses in solar device operation.
To confront this challenge, the researchers developed a novel, robust passivator with meticulously engineered functional groups. These groups provide anchoring interactions strong enough to remain affixed to the perovskite surface irrespective of its termination chemistry, a critical feature given the diverse surface compositions encountered during device fabrication. This strategic molecular design effectively prevents passivator desorption, even under combined thermal and illumination stresses that typically induce deterioration in other systems. The result is a dramatic improvement in the durability and efficiency of wide-bandgap perovskite solar cells, marking a significant step forward in tandem solar technology.
The implications of this robust passivation extend beyond mere stability. The researchers observed substantial suppression of phase segregation within the perovskite layer—a common phenomenon where halide ions redistribute unevenly under illumination and heat, forming iodide-rich and bromide-rich domains that degrade device performance. By stabilizing the composition and structure of the perovskite, the newly designed passivator not only prolongs the operational lifetime but also maintains optimal energy band alignment and charge transport properties essential for high-efficiency energy conversion.
Experimentally, wide-bandgap perovskite solar cells treated with the new passivation technique achieved a champion power conversion efficiency of 23.5%. More impressively, these devices exhibited negligible efficiency loss after enduring 1,000 hours of continuous 1-sun illumination at around 50 °C—conditions that closely mimic real-world operational environments. This remarkable stability benchmark addresses one of the principal impediments in transitioning perovskite solar technology from laboratory-scale prototypes to commercial modules capable of durable performance.
Building upon these advancements, the team incorporated such optimized perovskite cells into monolithic tandem architectures with Cu(In,Ga)Se₂ bottom cells. Tandem cells harness the synergistic capture of a broader solar spectrum, effectively surpassing the Shockley-Queisser limit for single junction cells. With the integrated approach, the tandem devices realized an outstanding steady-state power conversion efficiency of 27.93%, which was certified at 27.35%, positioning them among the highest-efficiency tandem cells incorporating CIGS reported to date.
Beyond their efficiency milestones, these tandem devices demonstrated impressive operational stability, maintaining consistent performance over 420 hours at approximately 38 °C in ambient air without encapsulation. This operational longevity under realistic environmental conditions hints at the tangible potential for commercial deployment, as stability has historically been the Achilles’ heel of perovskite-based photovoltaics. Such durability coupled with high efficiency could ultimately accelerate the market adoption of perovskite/CIGS tandem technology for applications demanding lightweight and flexible photovoltaics.
The success of this study is not only a technical feat but also provides critical insight into the fundamental chemistry governing perovskite stability. By elucidating the mechanisms behind passivator desorption and its impact on defect dynamics and phase stability, the work offers a new roadmap for molecular engineering in perovskite research. This approach paves the way for future developments wherein passivator molecules can be systematically optimized based on the underlying surface chemistry and operational stress profiles.
An interesting facet of this research is its practical relevance. Many passivation strategies that have shown promise under idealized conditions fail to translate into durable performance when tested under simultaneous illumination and thermal stress. The new material directly addresses this gap, validating the importance of testing under realistic accelerated aging conditions. It suggests that future standards for perovskite passivation must incorporate such rigorous stress tests to ensure genuine improvements in device stability.
Furthermore, the integration of wide-bandgap perovskites with Cu(In,Ga)Se₂ thin films leverages two well-established photovoltaic technologies, combining the flexibility and tunability of perovskites with the proven stability and manufacturability of CIGS. This tandem configuration exploits complementary absorption edges, thereby maximizing the utilization of incident solar energy. The demonstrated efficiencies bring this hybrid tandem design close to the commercial viability threshold, bridging the longstanding gap between academia and industry for tandem solar applications.
There remain challenges and avenues for further research. Although the newly developed passivator significantly enhances stability, long-term outdoor testing and scaling up device sizes will be essential to fully validate commercial prospects. Additionally, the cost-effectiveness and synthesis scalability of such specialized passivators will need assessment to determine the feasibility of mass production. Nonetheless, this breakthrough sets a new precedent in material design principles that will likely inspire parallel innovations across the photovoltaic community.
In conclusion, the study presented by Pei and colleagues represents a pivotal advancement in tandem solar cell technology. By ingeniously circumventing the limitations of passivation under operational stresses, it not only improves the power output and lifespan of wide-bandgap perovskite cells but also enables record efficiencies in perovskite/CIGS tandems. This breakthrough substantiates the claim that carefully engineered molecular interactions at the perovskite interface are the keys to unlocking robust, high-performance tandem solar cells capable of revolutionizing the renewable energy landscape.
As the world urgently seeks sustainable and scalable energy solutions, such technological innovations provide hope and direction. The convergence of molecular-level chemistry, materials engineering, and device physics embodied in this work exemplifies the multidisciplinary effort necessary to propel solar energy into a new era. The successful certification of a 27.35% efficient perovskite/Cu(In,Ga)Se₂ tandem cell heralds a future where solar energy is not only more efficient but also more resilient and accessible globally.
Looking ahead, the principles elucidated here could well translate into improvements across various perovskite-based optoelectronic devices, including light-emitting diodes and photodetectors, broadening the impact of this research. More immediately, the demonstrated combination of stability and efficiency underscores the readiness of tandem perovskite/CIGS cells for near-term industrial consideration and scale-up, further energizing the race towards sustainable energy transition.
This research invites the scientific community to rethink stability paradigms and to prioritize molecular design that harmonizes with operational realities. It serves as a compelling reminder that breakthroughs often stem from detailed attention to interfacial chemistry, which governs the delicate balance between performance and durability. As a result, the future of photovoltaic innovation shines brighter than ever, reaffirming the central role of perovskite tandem technologies in the global renewable energy portfolio.
Subject of Research: Development of a robust defect passivation strategy for wide-bandgap perovskite solar cells integrated with Cu(In,Ga)Se₂ in monolithic tandem architectures.
Article Title: Inhibiting defect passivation failure in perovskite for perovskite/Cu(In,Ga)Se₂ monolithic tandem solar cells with certified efficiency 27.35%.
Article References:
Pei, F., Lin, S., Zhang, Z. et al. Inhibiting defect passivation failure in perovskite for perovskite/Cu(In,Ga)Se₂ monolithic tandem solar cells with certified efficiency 27.35%. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01761-5
Image Credits: AI Generated
