Perovskite solar cells have advanced rapidly in efficiency, but sunlight itself remains a source of damage. High-energy ultraviolet irradiation can oxidize halide ions, accelerate iodide migration, trigger component loss, and create deep defects that degrade device performance. In a new study published in
Research, researchers from Northwestern Polytechnical University and collaborating institutions report a molecular strategy that addresses this problem from within the perovskite layer rather than simply blocking UV light from outside.
The researchers introduced 2,3-bis(2,4,5-trimethyl-3-thienyl) maleimide, known as BTTM, into metal halide perovskites. BTTM is a photoisomeric molecule that can reversibly switch between structural states under ultraviolet and visible light. This light-responsive behavior allows it to act as more than a passive additive. Through chemical interactions with the perovskite lattice, it helps anchor mobile ions and stabilize the material during UV exposure.
The key mechanism is ion anchoring. The carbonyl groups in BTTM interact with lead in the perovskite lattice, while N–H groups form hydrogen-bonding interactions with iodide. Together, these interactions stabilize the Pb–I octahedral framework, passivate defects, and suppress iodide migration. This is important because UV irradiation can drive iodide oxidation and iodine formation, which then accelerates vacancy formation, component loss, and structural degradation.
BTTM also improves film quality. With an optimized additive concentration, the perovskite films showed larger grains, more oriented crystal growth, reduced residual PbI₂, smoother morphology, lower residual tensile stress, stronger photoluminescence, and longer carrier lifetime. The carrier lifetime increased from 126.41 to 340.82 nanoseconds, indicating reduced nonradiative recombination. These improvements help explain the increase in open-circuit voltage and overall device performance.
Under UV aging, the difference became more pronounced. Control films showed signs of iodine release, photoluminescence loss, PbI₂ formation, crystal degradation, and surface-potential changes. BTTM-modified films retained stronger optical emission, more stable crystal features, and better film uniformity. Device measurements also showed reduced hysteresis and lower dark current, consistent with suppressed ion migration and reduced charge recombination.
The performance gains were substantial. The optimized BTTM perovskite solar cell reached a power conversion efficiency of 24.71%, compared with 22.07% for the control device. The stabilized power output reached 24.12%, and the strategy also improved performance in wide-bandgap perovskite devices. In nitrogen storage tests using unencapsulated devices, BTTM-based cells retained 96.9% of their initial efficiency after 1,000 hours, while control devices retained only 54.3%. Under cumulative UV irradiation of 5 kWh/m², BTTM devices retained about 90% of their initial efficiency, compared with about 60% for unmodified devices.
The study does not mean that all long-term stability challenges in perovskite photovoltaics have been solved. Outdoor operation involves heat, moisture, oxygen, mechanical stress, and full-spectrum sunlight, and the present strategy still needs further validation in encapsulated modules and real-world conditions. Even so, the work provides a simple and mechanistically informed additive approach for improving UV resistance. By combining defect passivation, ion anchoring, and light-responsive molecular behavior, BTTM offers a useful design direction for more durable perovskite solar cells in high-UV environments.
The complete study is accessible via DOI: 10.34133/research.1196