Eco-Friendly Preparation of High-Quality Lead-Free Halide Ferroelectric Solid-Solution Toward High-Performance X-ray...

Bismuth and antimony-based halide ferroelectrics represent a significant class of materials for sustainable electronics. Prior research has shown that these compounds offer superior environmental stability and reduced toxicity compared to traditional lead-based perovskites. The intrinsic spontaneous polarization within these crystalline structures facilitates efficient charge separation in optoelectronic devices. Existing materials often suffer from excessively wide electronic bandgaps that limit light absorption and energy conversion efficiency. The charge-carrier mobility-lifetime product in these systems typically remains too low for high-performance sensing applications. Conventional synthesis methods frequently rely on hazardous organic solvents that contradict the ecological benefits of lead-free compositions. This absence of evidence motivated the exploration of biomass-derived solvent systems and alloying strategies to optimize semiconductor properties.

This research targets the synthesis of high-quality (HDA)Sb1-xBixI5 crystals to overcome performance bottlenecks in lead-free radiation detectors. The investigators sought to implement a sustainable crystallization process using gamma-valerolactone as a green alternative to toxic precursors. The study focuses on the rational engineering of the antimony-to-bismuth ratio to tune the electronic structure of the resulting solid-solution. Researchers aimed to demonstrate that alloying can significantly enhance the transport properties of charge carriers within the ferroelectric lattice. The project evaluates the feasibility of using these engineered crystals for self-powered X-ray sensing without external voltage bias. The team intended to establish a benchmark for sensitivity and detection limits within the category of halide ferroelectric materials. The work addresses the need for scalable, eco-friendly production routes for advanced semiconductor single crystals.

The experimental protocol utilized an isothermal evaporation technique to grow centimeter-sized single crystals of (HDA)Sb1-xBixI5. Hexane-1,6-diammonium (HDA) served as the organic cation template for the formation of the hybrid halide framework. The biomass-derived solvent gamma-valerolactone (GVL) provided a stable medium for the controlled precipitation of the solid-solution phases. Scientists varied the stoichiometric ratio of antimony to bismuth from x = 0 to x = 1 to identify the optimal composition for optoelectronic response. Characterization of the material involved measuring the electronic bandgap to assess the impact of bismuth substitution on the energy levels. The team fabricated X-ray detectors to quantify the charge-carrier mobility-lifetime product and the resulting sensitivity under radiation exposure. Performance testing included the determination of the lowest detectable dose rate and the evaluation of self-powered operation modes.

The engineered (HDA)Sb0.39Bi0.61I5 composition achieved a record-narrow bandgap of 1.64 eV for this class of materials. Substitution of bismuth into the antimony-based lattice increased the charge-carrier mobility-lifetime product by approximately two orders of magnitude. The resulting X-ray detector demonstrated a high self-powered sensitivity of 1,040 uC Gyair-1 cm-2 under zero-bias conditions. The device reached an exceptionally low detection limit of 0.25 nGyair s-1, indicating high precision for low-dose radiation monitoring. Maximum sensitivity values peaked at 17,560 uC Gyair-1 cm-2, surpassing all previously reported halide ferroelectric detectors. The centimeter-sized single crystals exhibited high structural quality and long-term environmental stability during the testing phases. The intrinsic ferroelectric spontaneous polarization effectively drove the collection of photo-generated charges without requiring an external power source.

The successful synthesis of (HDA)Sb0.39Bi0.61I5 demonstrates that solid-solution strategies can effectively bridge the performance gap in lead-free semiconductors. The use of gamma-valerolactone establishes a viable pathway for the green manufacturing of high-performance electronic components. These findings suggest that Bi/Sb-based halide ferroelectrics are suitable candidates for next-generation, low-dose X-ray imaging systems. The high sensitivity and low detection limit provide a foundation for developing safer medical diagnostic tools and industrial inspection sensors. Future research may expand this alloying approach to other hybrid halide systems to further refine their optoelectronic properties. The integration of ferroelectric polarization into detector design offers a sustainable route toward energy-efficient, self-powered radiation monitoring. This work provides a comprehensive framework for the rational design of environmentally friendly materials for advanced optoelectronic applications.