A group of research ers from Beijing Institute of Technology, National Institute of Clean-and-Low-Carbon Energy , Beijing Engineering Research Center of Nano-structured Thin Film Solar Cells and Beijing University of Chemical Technology , has developed a coordination-regulated strategy to stabilize wide-bandgap perovskites for efficient perovskite/CIGS tandem solar cells. By introducing bis(2-pyridylmethyl) sulfide (2PyS) to regulate the local Pb 2+ coordination environment, the researchers suppressed defect formation, reduced halide ion migration, and mitigated photoinduced phase segregation. The optimized wide-bandgap perovskite solar cells achieved an efficiency of 22.21% and retained more than 91% of their initial performance after 2000 hours of continuous operation. When integrated with a CIGS bottom cell, the resulting four-terminal perovskite/CIGS tandem solar cell delivered an overall efficiency of 29.71%. This study provides a promising molecular design route toward stable and efficient tandem photovoltaics.
Wide-bandgap perovskites are essential light absorbers for tandem solar cells, where they can be paired with narrow-bandgap materials such as crystalline silicon or Cu(In,Ga)Se 2 (CIGS) to overcome the efficiency limit of single-junction photovoltaics. Their tunable bandgaps and excellent optoelectronic properties make them attractive candidates for next-generation solar technologies. However, wide-bandgap perovskites commonly rely on mixed-halide compositions, which are vulnerable to halide ion migration under illumination and thermal stress. This migration can lead to the formation of iodine-rich and bromine-rich domains, causing spatial bandgap inhomogeneity, enhanced non-radiative recombination, and rapid performance degradation. Therefore, stabilizing wide-bandgap perovskites under real operating conditions remains a major challenge for high-performance tandem solar cells.
A key origin of this instability is the presence of undercoordinated Pb 2+ defects and associated halide vacancies. These defects not only act as recombination centers but also disturb the local lattice environment and provide pathways for halide ion migration. Conventional post-treatment passivation strategies can reduce some defects after crystallization, but they often offer limited control over defect formation during the film growth process. As a result, photoinduced halide segregation remains difficult to suppress during long-term device operation.
The Solution: The group researchers reported a coordination-regulated defect suppression strategy by introducing bis(2-pyridylmethyl) sulfide (2PyS) into wide-bandgap perovskite films. The 2PyS molecule strongly coordinates with Pb 2+ ions and modulates the local coordination environment during film formation. This interaction reduces the density of undercoordinated Pb 2+ defects and suppresses the formation of halide vacancies, so limiting defect-assisted ion migration and mitigating photoinduced halide segregation.
Theoretical calculations showed that 2PyS has stronger binding with PbI 2 than commonly used organic solvents such as Dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO), indicating its dominant role in regulating Pb 2+ coordination during crystallization. Moreover, in situ photoluminescence measurements further revealed that 2PyS modulates crystallization kinetics, suppresses rapid nucleation, and promotes more homogeneous film growth. As a result, the modified perovskite films exhibit improved optoelectronic properties, reduced non-radiative recombination, enhanced structural integrity, and stronger phase stability under coupled illumination and thermal stress.
The optimized wide-bandgap perovskite solar cells achieved a power conversion efficiency of 22.21% with an open-circuit voltage of 1.20 V. The devices also exhibited significantly improved operational stability, retaining more than 91% of their initial efficiency after 2000 hours of continuous operation. Furthermore, the semi-transparent wide-bandgap perovskite top cell was integrated with a CIGS bottom cell to construct a four-terminal tandem solar cell, achieving an overall efficiency of 29.71%. These results demonstrate the great potential of coordination chemistry for stabilizing wide-bandgap perovskites and enabling efficient tandem photovoltaic devices.
The Future: Future research will focus on designing more coordination-active molecules with tailored binding configurations, appropriate steric structures, and multifunctional passivation capabilities. Such molecular engineering may enable more precise control over crystallization kinetics, defect formation, and ion migration in wide-bandgap perovskites. Advanced operando characterization techniques will also be important for revealing the dynamic evolution of defects, halide redistribution, and phase segregation under realistic operating conditions. Extending this coordination-regulated strategy to higher-bandgap perovskites, all-perovskite tandems, perovskite/silicon tandems, and large-area perovskite/CIGS modules represents a promising direction toward commercialization.
The Impact: This work highlights the critical role of coordination chemistry in controlling defect formation and phase stability in wide-bandgap perovskites. By targeting defect formation at its origin, the strategy provides an effective pathway to suppress halide ion migration and photoinduced phase segregation, two long-standing obstacles in wide-bandgap perovskite photovoltaics. The demonstrated 29.71% four-terminal perovskite/CIGS tandem solar cell shows the practical potential of this approach for high-efficiency, stable tandem solar energy conversion.
The research has been recently published in the online edition of Materials Futures, an international journal in the field of interdisciplinary materials science research.
Reference: Chenxi Wu, Shuping Lin, Zhongyang Zhang, Yao Sun, Teng Cheng, Quanhong Han, Mengqi Guo, Jiahong Tang, Minghua Li, Dongxu Lin, Dalong Zhong, Ying Zhao, Yan Jiang. Coordination-regulated defect suppression enables stable wide-bandgap perovskites for efficient perovskite/CIGS tandem solar cells[J]. Materials Futures , 2026, 5(3): 035106. DOI: 10.1088/2752-5724/ae7817
Materials Futures
Coordination-regulated defect suppression enables stable wide-bandgap perovskites for efficient perovskite/CIGS tandem solar cells
2-Jul-2026