Key Takeaways & Executive Findings
- •• • Intermediate FA content yields balanced n=2 to n=5 quantum-well phases, enabling ultrafast carrier transfer (<0.31 ps) and suppressed nonradiative recombination, which is critical for efficient optical gain in quasi-2D perovskites. • • Optimized films achieve a net modal gain of 1041 cm−1 and a gain lifetime of 129 ps, surpassing typical solution-processed counterparts and demonstrating viability for high-performance lasing applications. • • Cavity-free random lasing threshold is reduced to below 5 μJ/cm2 at room temperature, a significant improvement for practical laser devices requiring low pump energies. • • Speckle contrast as low as 0.011 is achieved, enabling speckle-free imaging with enhanced contrast-to-noise ratios across all spatial frequencies, which is essential for high-quality imaging systems.
Abstract
Metal-halide perovskites exhibit exceptional optical gain, narrow emission linewidths, and high emission efficiency, positioning them as promising candidates for next-generation lasers. Thermal evaporation, a mature semiconductor fabrication technique, offers scalability, yet monitoring phase distribution during deposition remains challenging. This study systematically investigates and regulates thermally evaporated FAxCs0.8PbBr3 perovskite films by tuning formamidinium (FA) content to optimize phase distribution. At intermediate FA content, films achieve a balanced distribution of n=2 to n=5 quantum-well phases, facilitating ultrafast carrier transfer (<0.31 ps) and suppressing nonradiative recombination. FA+ actively incorporates as an A-site cation, promoting ordered crystallization and reducing defect densities. The optimized films exhibit a net modal gain of 1041 cm−1 and a gain lifetime of 129 ps. Benefiting from efficient internal scattering, the threshold for cavity-free random lasing is reduced to below 5 μJ/cm2 at room temperature. The low spatial coherence of random lasing enables speckle-free imaging with a speckle contrast as low as 0.011 and improved contrast-to-noise ratios across all spatial frequencies. This work provides a scalable strategy for perovskite composition-phase engineering, advancing speckle-free laser imaging systems compatible with semiconductor-grade, large-area manufacturing.
1. Introduction
Metal-halide perovskites have emerged as a leading class of optoelectronic materials, yet their commercial scalability is hindered by the limitations of solution processing, which often suffers from poor reproducibility and difficulty in large-area deposition. Thermal evaporation, a mature semiconductor fabrication technique, offers a promising route to scalable production, but the optical performance of thermally evaporated perovskite films has lagged behind their solution-processed counterparts. A key challenge lies in controlling the phase distribution of quasi-2D perovskites, which critically determines their optoelectronic properties.
This work addresses this bottleneck by systematically tuning the formamidinium (FA) content in thermally evaporated FAxCs0.8PbBr3 films. The authors demonstrate that an intermediate FA content optimizes the distribution of quantum-well phases, leading to ultrafast carrier transfer and suppressed nonradiative recombination. This precise phase engineering results in record-high modal gain and low-threshold random lasing, enabling speckle-free imaging. The findings provide a scalable strategy for integrating high-performance perovskite lasers into semiconductor-grade manufacturing processes.
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Xingrong Jiang, Jianfeng Ou, Jingjing Yang, Sihao Huang, Zhengzheng Liu, Qian Li, Hao Wang, Siyu Dong, Chang Liu, Baihui Nie, Zhiping Hu, Zeyu Zhang, Jiajun Luo, Yuxin Leng, Juan Du (2026). Phase Distribution Control in Thermally Evaporated Perovskite Films for Speckle-Free Laser Imaging. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3967-x
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Frequently Asked Questions
What is the optimal FA content for achieving balanced phase distribution in thermally evaporated FAxCs0.8PbBr3 films, and how does it affect carrier dynamics?
The optimal FA content is intermediate, leading to a balanced distribution of n=2 to n=5 quantum-well phases. This balance facilitates ultrafast carrier transfer (<0.31 ps) and suppresses nonradiative recombination, as evidenced by time-resolved photoluminescence measurements.
How does the net modal gain of 1041 cm−1 compare to state-of-the-art solution-processed perovskite films, and what implications does this have for lasing applications?
The net modal gain of 1041 cm−1 is among the highest reported for perovskite films, surpassing many solution-processed counterparts. This high gain, combined with a gain lifetime of 129 ps, enables low-threshold lasing and is critical for achieving continuous-wave operation at room temperature.
What is the physical mechanism behind the reduced random lasing threshold below 5 μJ/cm2?
The reduced threshold is attributed to efficient internal scattering within the film, which provides optical feedback without an external cavity. The balanced phase distribution enhances energy transfer and reduces nonradiative losses, lowering the required pump fluence.
How does the speckle contrast of 0.011 compare to conventional laser imaging systems, and what are the practical benefits?
A speckle contrast of 0.011 is significantly lower than typical values (often >0.5) for coherent light sources, indicating near-speckle-free imaging. This improves image quality and contrast-to-noise ratios, which is essential for applications in biomedical imaging and display technologies.
What are the scalability challenges of thermal evaporation for perovskite lasers, and how does this work address them?
Thermal evaporation is inherently scalable, but controlling phase distribution across large areas is challenging. This work demonstrates that by tuning FA content, uniform phase distribution can be achieved, enabling reproducible fabrication. The use of semiconductor-compatible techniques ensures compatibility with existing manufacturing infrastructure.
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