In the rapidly evolving landscape of renewable energy technologies, perovskite solar cells have emerged as one of the most promising candidates for next-generation photovoltaic devices. Their potential for high efficiency coupled with low-cost fabrication methods has spurred intense global research efforts. Yet, despite impressive improvements in power conversion efficiencies, widespread commercial adoption of perovskite solar cells has been hindered by challenges related to their operational and thermal stability. A new study spearheaded by Kim et al. introduces a groundbreaking approach to addressing these issues by replacing a commonly used liquid additive with a non-volatile solid-state alternative, thereby pushing the stability and performance metrics of n–i–p perovskite solar cells to unprecedented heights.
Traditionally, liquid-state 4-tert-butylpyridine (4TBP) has been an essential component in the formulation of perovskite solar cells operating under the n–i–p (n-type/intrinsic/p-type) architecture. Its capacity to dissolve lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopants and stabilize lithium ions within the hole transport layer (HTL) enhances charge transport and boosts overall efficiency. However, researchers have long recognized the limitations posed by 4TBP. Its high volatility and corrosive attributes promote degradation pathways in the perovskite absorber layer, accelerating the formation of pinholes and byproducts under thermal stress. Such structural weaknesses compromise the long-term operational stability, severely restricting device lifetimes crucial for real-world applications.
The challenge has been to find an alternative that preserves or enhances the beneficial properties of 4TBP—namely, lithium ion stabilization and dopant dissolution—without the detrimental effects induced by volatility and corrosivity. The solution offered by Kim and colleagues is the introduction of 4-(N-carbazolyl)pyridine (4CP), a solid-state additive that exhibits significantly different physicochemical characteristics while maintaining a chemical affinity for lithium ions. Compared to 4TBP, 4CP is non-volatile and structurally stable under harsh thermal environments, enabling it to sustain the integrity of perovskite solar cells during prolonged operational periods.
The study’s comprehensive analyses illustrate that 4CP not only facilitates the formation of LiTFSI complexes but also mitigates the occurrence of byproducts and pinholes that traditionally plague HTLs in devices with liquid additives. Employing 4CP results in a homogenized, defect-minimized hole transport network, which directly translates into enhanced charge extraction and minimized recombination losses. Such improvements at the microscopic layer level are pivotal to the macro performance shifts observed in fabricated devices.
Performance metrics presented in the study showcase the transformative impact of this single substitution. Perovskite solar cells incorporating 4CP have attained a remarkable power conversion efficiency (PCE) of 26.2%, with independent certification confirming a consistent 25.8%. These values represent some of the highest efficiencies recorded for stable n–i–p perovskite devices to date. Achieving such efficiencies while enhancing stability addresses a central trade-off that has stymied progress in perovskite photovoltaics: balancing efficiency with durability.
Beyond peak performance, the operational longevity of perovskite devices containing the new 4CP additive stands out. The devices maintain over 80% of their initial efficiency for more than 3,000 hours under maximum power point tracking (MPPT). This measurement, where the solar cell is continuously operated at its optimal load to mimic real-world energy harvest conditions, is a stringent test of stability rarely sustained over such prolonged timescales in perovskite research. Such robustness signals a substantial leap forward in bridging laboratory efficiencies and commercial viability.
Thermal stability under extreme cycling conditions is another critical performance indicator for photovoltaic materials. The unencapsulated cells doped with 4CP endured 200 thermal shock cycles, alternating between −80°C and 80°C, while preserving 90% of their initial efficiency. This resilience highlights 4CP’s efficacy in maintaining the physical and chemical integrity of the perovskite absorber and HTL despite drastic temperature fluctuations—a scenario frequently encountered in outdoor applications.
Further stress tests under continuous exposure at elevated temperatures (65°C and 85°C) reinforced the superiority of the 4CP-based devices, with prolonged performance retention underscoring their capacity to withstand thermal degradation processes that commonly lead to rapid performance deterioration in traditional 4TBP systems. The combination of high efficiency, thermal robustness, and operational longevity embodied in these devices places them at the forefront of perovskite solar technology development.
Mechanistically, 4CP’s stability attributes appear linked to its lower volatility and chemical affinity to lithium ions, which facilitates complex stabilization and inhibits degradation pathways that occur with volatile additives. Unlike 4TBP, which can evaporate and expose the perovskite layer to corrosive intermediates or moisture ingress, the solid-state additive remains anchored within the hole transport matrix. This behavior effectively suppresses the generation of pinholes, which act as pathways for environmental contaminants and cause localized defects detrimental to charge transport.
Moreover, the enhanced chemical environment around lithium ions fostered by 4CP likely suppresses ion migration—a key contributor to device hysteresis and long-term performance decline. Lithium ion stability is central to maintaining the electrical and structural integrity of the hole transport layer, making 4CP’s contribution as an additive a critical factor in the device stability equation. This insight opens new avenues for rational design of dopant-host interactions in perovskite solar cells, prioritizing solid-state, low-volatility materials that do not compromise interfacial charge dynamics.
The implications of this advancement transcend beyond incremental efficiency improvements. Stability concerns have long been cited as a fundamental bottleneck in the commercialization pathway of perovskite solar cells. By solving one of the primary degradation engines linked to additive volatility and corrosivity, Kim et al. provide a scalable, practical solution that can be integrated into existing n–i–p device architectures with minimal processing changes. This seamlessly aligns with manufacturing demands that emphasize reproducibility, longevity, and cost-effectiveness.
Furthermore, the study’s methodological approach—leveraging comprehensive material characterization, rigorous thermal cycling tests, and operational stress assessments—sets a new benchmark for evaluating next-generation additives and interfacial engineering strategies. It highlights the synergistic effect of combining dopant stabilization chemistry with morphology control in the hole transport layer, which could inspire parallel research in other critical perovskite interfaces such as electron transport layers and passivation treatments.
As the perovskite field races toward commercial deployment, the findings presented by Kim and colleagues demonstrate that addressing subtle chemical interactions at the molecular additive level can yield transformative outputs for device stability and performance. Given that outdoor photovoltaic modules face a complex array of thermal, mechanical, and chemical stresses, robust additives like 4CP offer a path to designing perovskite solar cells resilient enough to meet these multifaceted challenges.
Looking ahead, the integration of non-volatile solid-state additives may also unlock further improvements by enabling the incorporation of more aggressive doping levels or combining with novel HTL materials tailored for enhanced conductivity and environmental resilience. This study paves the way for a paradigm shift in how device interfaces are engineered to simultaneously optimize efficiency and durability in perovskite photovoltaics.
Ultimately, the breakthrough represented by 4-(N-carbazolyl)pyridine additive adoption is a milestone toward realizing perovskite solar cells that not only compete with silicon technologies in efficiency but also withstand the rigors of daily outdoor environments. It validates the underlying scientific principle that a meticulous choice of dopant-host chemistry—often viewed as auxiliary—can be the key to unlocking the true industrial potential of emerging photovoltaic materials.
Kim et al.’s work stands as a testament to the critical role of materials innovation at the nanoscale in shaping the future energy landscape. By bridging chemistry, material science, and device engineering, their findings could propel perovskite solar cells closer to widespread commercial success, contributing meaningfully to the global transition toward sustainable and affordable energy.
Subject of Research: Stability and performance enhancement of n–i–p perovskite solar cells through advanced hole transport layer additives.
Article Title: Non-volatile solid-state 4-(N-carbazolyl)pyridine additive for perovskite solar cells with improved thermal and operational stability.
Article References:
Kim, K., Yang, S., Kim, C. et al. Non-volatile solid-state 4-(N-carbazolyl)pyridine additive for perovskite solar cells with improved thermal and operational stability. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01864-z
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