New contact material boosts the efficiency of perovskite solar cells
Caborane based material offers multiple advantages by replacing the standard fullerene electron transport material, the study shows. The novel material is now commercially available
image:
The illustration shows a mCB-FMN on a PbI2-terminated FAPbI3 perovskite surface.
view moreCredit: Lea Zimmermann / HZB
A newly developed material for the electron contact improves the efficiency of single perovskite solar cells and perovskite/silicon tandem solar cells. The new material is based on a carborane molecule. It offers several advantages over the standard material C60, as shown by the study led by Steve Albrecht’s team. The new material has since been patented and is already commercially available.
Perovskite solar cells are not only exceptionally inexpensive to manufacture but also achieve very high efficiency levels. Single-junction perovskite devices already can convert over 27 per cent of sunlight into electrical energy, while perovskite-silicon tandem cells have even achieved efficiencies of over 35 per cent. Until now, a layer of so-called ‘football molecules’ (C60) has been used to transport electrons away. However, a significant proportion of the charge carriers are lost at the interface between the C60 layer and the perovskite absorber. Furthermore, C60 materials are relatively expensive and tend to delaminate over time, compromising the cell’s stability.
Novel material developed
In collaboration with a group from Kaunas University of Technology (KTU) in Lithuania and other partners, the team led by Professor Steve Albrecht at HZB has now developed a novel carborane-based material. Not only can it replace C60 electron-transport materials, it is also superior in many respects. The material can be produced from commercially available reagents. The molecules consist of a meta-carborane core with two 9-fluorenylidene malononitrile functional groups (mCB-FMN).
Multiple advantages
Compared to C60, the thin film can be deposited from the vapour phase at lower temperatures. This means that the production of the layer requires less energy and places less thermal stress on the equipment. The evaporated mCB-FMN forms a uniform layer on the perovskite absorber. Measurements of transient surface photovoltage (trSPV) and photoluminescence (PL) reveal that this layer facilitates the transport of electrons very effectively with fewer losses at the interface than with C60. Investigations using He-I ultraviolet photoemission spectroscopy (He-UPS) showed that the mCB-FMN layer and the perovskite absorber layer are well matched energetically. Density functional theory (DFT) calculations suggest that surface defects are passivated, which could be a further reason for the lower losses. Electron microscopy and in-situ ellipsometry during deposition of the overlying SnOx buffer layer demonstrate that the new ETM even improves film growth. Mechanical tests confirm that the new material also enhances interfacial adhesion and, consequently, stability within the perovskite/ETM/SnOx layer stack.
Improved efficiency
As a result, the efficiency of a single p-i-n perovskite cell increases by 1.5% (in absolute terms) when the new ETM replaces C60. In perovskite-silicon tandem cells, the efficiency increases by as much as 2.4% (in absolute terms) compared to the reference cell. This is because the lower parasitic absorption also allows more light to reach the photoactive layers.
‘We have developed a very high-performance substitute material for fullerenes in perovskite solar cells, and we have demonstrated its benefits through different measurements,’ says Lea Zimmermann, first author of the study.
Already commercially available
The new material has already attracted considerable interest in both academic and industrial circles, and it was selected for the “Best Scientific Content Award” at the 2025 TandemPV International Workshop. A European patent application has been filed (EP 25175871.0) has been filed, covering mCB-FMN, its derivatives and their use in solar cells. ‘Dyenamo has now brought this material to market with the aim of enabling its widespread use,’ explains Steve Albrecht.
Novel materials for tandem solar cells
His team had already achieved a breakthrough with self-assembling monolayers (SAMs) for the hole-conducting contact layers on the other side of the solar cell, in collaboration with international partners. They are now aiming to achieve the same for the electron transport layer: ‘We are currently working flat out on developing further novel materials in this class and we believe that this class of materials could also revolutionise tandem solar cells,’ says Albrecht.
Journal
Energy & Environmental Science
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
A novel carborane-based electron transport material for high-performance perovskite/silicon tandem solar cells
Article Publication Date
17-Jul-2026
Coordination chemistry unlocks stable wide-bandgap perovskites for high-efficiency tandem solar cells
Materials Futures
image:
2PyS Coordination Enables Stable Wide-Bandgap Perovskites
view moreCredit: Yan Jiang from Beijing Institute of Technology.
A group of researchers 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 Pb2+ 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)Se2 (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 Pb2+ 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 Pb2+ ions and modulates the local coordination environment during film formation. This interaction reduces the density of undercoordinated Pb2+ 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 PbI2 than commonly used organic solvents such as Dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO), indicating its dominant role in regulating Pb2+ 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
Journal
Materials Futures
Article Title
Coordination-regulated defect suppression enables stable wide-bandgap perovskites for efficient perovskite/CIGS tandem solar cells
Article Publication Date
Coordination chemistry unlocks stable wide-bandgap perovskites for high-efficiency tandem solar cells
Peer-Reviewed Publication
Materials Futures
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Coordination Chemistry Unlocks Stable Wide-Bandgap Perovskites for High-Efficiency Tandem Solar Cells
image:
2PyS Coordination Enables Stable Wide-Bandgap Perovskites
view more
Credit: Yan Jiang from Beijing Institute of Technology.
A group of researchers 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 Pb2+ 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)Se2 (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 Pb2+ 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 Pb2+ ions and modulates the local coordination environment during film formation. This interaction reduces the density of undercoordinated Pb2+ 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 PbI2 than commonly used organic solvents such as Dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO), indicating its dominant role in regulating Pb2+ 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
Journal
Materials Futures
DOI
10.1088/2752-5724/ae7817
Article Title
Coordination-regulated defect suppression enables stable wide-bandgap perovskites for efficient perovskite/CIGS tandem solar cells
Article Publication Date
22-Jul-2026
