How Chalcohalides Are Powering a Brighter Future
High Efficiency
Eco-Friendly
Enhanced Stability
Versatile Applications
For over a decade, lead-halide perovskites have been the rockstars of the solar energy world, promising remarkable efficiency at low cost. But behind the glittering performance, a tarnish remains: concerns about lead toxicity and long-term instability have cast a shadow on their future 1 4 . Scientists have been urgently searching for a new class of materials that can match the solar-capturing prowess of perovskites without their drawbacks. Enter chalcohalides, an emerging family of semiconductors that are quietly forging a path toward a more stable, efficient, and earth-abundant energy future 4 5 .
The name "chalcohalide" itself reveals its hybrid nature, combining chalcogen anions (like sulfur or selenium) with halogen anions (like bromine or iodine) 4 .
Imagine taking the best ingredients from two famous families of materials—the superior electronic properties of halide perovskites and the renowned robustness of metal chalcogenides—and blending them into one super-material. This "split-anion" approach creates a more covalent chemical bonding environment, which translates to the enhanced chemical and thermal stability that has eluded pure halide perovskites 1 4 . Furthermore, by using metals like antimony (Sb) and bismuth (Bi), which have a similar electronic configuration to lead, scientists can tap into the same defect-tolerant properties that make perovskites so efficient, while moving beyond toxicity concerns 1 4 .
What makes chalcohalides so exciting for scientists and engineers is their multifunctionality. They are not one-trick ponies suited only for solar panels. Their tunable properties make them promising candidates for a wide range of technologies, from photodetectors and light-emitting diodes (LEDs) to photocatalysis for fuel production and even thermoelectric devices that convert waste heat into electricity 2 4 .
The secret to this versatility lies in the "ns2 lone pair" of electrons found in p-block metals like Sb and Bi 4 . This unique electronic feature contributes to highly dispersive band edges—essentially, "highways" for electrons to travel through the material with ease. This results in high carrier mobility, a critical property for efficient electronic devices 1 4 . Moreover, the ability to mix and match different chalcogens and halogens allows researchers to fine-tune the material's bandgap—the minimum energy needed to kick an electron into a conductive state—to perfectly suit a specific application, whether it's capturing a particular color of light or operating efficiently under harsh conditions 1 8 .
High efficiency photovoltaic conversion with enhanced stability compared to traditional perovskites.
Tunable bandgap enables precise color emission for next-generation displays and lighting.
Efficient conversion of sunlight into chemical energy for fuel production and environmental remediation.
Conversion of waste heat into electricity, improving energy efficiency across industries.
The development of chalcohalides relies on a precise combination of elements, each playing a critical role in the final material's properties. The table below details some of the essential components.
| Material Category | Specific Examples | Function in Research |
|---|---|---|
| Metal Cations | Antimony (Sb), Bismuth (Bi) | Form the crystal structure's backbone; their "ns2" lone-pair electrons enable defect tolerance and strong light absorption 4 . |
| Chalcogen Anions | Sulfur (S), Selenium (Se) | Provide covalent character to chemical bonds, enhancing thermal and chemical stability 1 4 . |
| Halogen Anions | Iodine (I), Bromine (Br) | Contribute to the unique crystal structure and help tune electronic properties like the bandgap 1 . |
| Halide Sources | SbI₃, BiBr₃, etc. | Highly purified compounds used as precursors to introduce halogen elements into the material during synthesis 1 . |
To understand how these materials are born, let's look at a landmark experiment from a 2025 study that successfully synthesized the entire family of eight (Sb,Bi)(S,Se)(Br,I) chalcohalides in a parallel exploration 1 . This systematic approach allowed scientists to draw clear comparisons and establish fundamental structure-property relationships.
The process began with the thermal co-evaporation of elemental sources (e.g., Sb and Se) onto a substrate heated to 280°C. This immediate reaction formed a binary chalcogenide precursor, like Sb₂Se₃.
This precursor was then placed in a sealed Petri dish with a specific halide source (e.g., SbI₃) and subjected to reactive annealing in a steel tubular furnace. This high-pressure, high-temperature step was the crucial moment where the halogen was incorporated, transforming the binary precursor into the final ternary chalcohalide crystal, such as SbSeI 1 .
The conditions for this second step—temperature, pressure, and duration—were meticulously optimized for each unique composition, demonstrating the precision required in materials science 1 .
| Compound | Temperature (°C) | Pressure (bar) | Time (minutes) |
|---|---|---|---|
| SbSI | 300 | 2.0 | 15 |
| SbSBr | 325 | 2.5 | 15 |
| BiSI | 425 | 2.5 | 15 |
| BiSBr | 400 | 2.5 | 15 |
| SbSeI | 450 | 3.0 | 15 |
| SbSeBr | 450 | 4.0 | 15 |
| BiSeI | 500 | 4.0 | 15 |
| BiSeBr | 450 | 4.0 | 15 |
The results were striking. The team discovered that this method produced chalcohalides with a unique quasi-one-dimensional, ribbon-like structure 1 8 . This anisotropic morphology is a hallmark of this family and leads to direction-dependent properties that could be harnessed in novel devices.
Most importantly, by simply switching the metal, chalcogen, or halogen, they could finely tune the material's optical bandgap across a wide range from 1.38 eV to 2.08 eV 1 . This covers key portions of the solar spectrum, making different compounds ideal for various applications. For instance, a bandgap around 1.4 eV is considered ideal for single-junction solar cells. Advanced photoluminescence measurements showed sharp, single-component emission peaks, indicating high material quality, and revealed how carrier dynamics and electron-phonon interactions govern their ultimate performance 1 .
| Material | Experimental Bandgap (eV) | Potential Application |
|---|---|---|
| SbSI | ~1.7 - 2.0 | Photovoltaics, Ferroelectric Devices |
| BiSeI | ~1.3 - 1.7 | Photovoltaics, Radiation Detection |
| BiSI | ~1.5 - 1.8 | Photovoltaics, Photocatalysis |
| SbSeBr | ~1.7 - 2.1 | Photodetectors |
The implications of this research extend far beyond a single experiment. The ability to systematically engineer chalcohalides opens up a new materials platform for a sustainable energy future. Functional devices, including photocatalytic systems for fuel production and prototype solar cells, have already demonstrated the practical viability of these materials 5 8 .
Developing methods for large-scale synthesis while maintaining material quality and performance.
Further improving power conversion efficiency to compete with established photovoltaic technologies.
The journey is far from over. Challenges in scaling up production, optimizing device interfaces, and further improving efficiency remain the focus of intense global research 5 . However, the foundation has been firmly laid. Chalcohalides represent a powerful blueprint for the inverse design of next-generation optoelectronic materials—materials that are not only high-performing but also stable, earth-abundant, and safe. As research continues to unlock their secrets, we may soon find our world powered by the versatile and promising shine of chalcohalides.