(Nanowerk Spotlight) Metal halide perovskites have attracted substantial research interest since 2009 when their potential for solar cell applications was first demonstrated. These semiconductor materials combine effective light absorption with good electrical conductivity while being simple to manufacture.
However, metal halide perovskites degrade rapidly under normal environmental conditions – a significant challenge that limits their practical applications. Scientists have tried various approaches to improve stability, including chemical modifications and protective coatings, but creating durable devices remains difficult. Most metal halide perovskite devices deteriorate within days or weeks under normal conditions, and within minutes when exposed to moisture, heat, or radiation.
Traditional methods for creating perovskite devices dissolve the materials in toxic solvents like dimethylformamide, spread them on surfaces, and heat them to form thin crystalline films. This process creates functional electronic materials but leaves them vulnerable to environmental damage. When exposed to moisture, the crystal structure degrades. Heat accelerates this degradation, and radiation exposure creates defects that reduce performance.
Reporting their findings in Advanced Energy Materials (“Enabling Optoelectronics in Harsh Environments: Laser-Printed Perovskite Films with Exceptional Stability Under Extreme Radiation, Thermal Stress, and Humidity”), researchers have now demonstrated a fundamentally different manufacturing approach. Instead of using solvents, they created a dry powder by combining methylammonium lead iodide (the perovskite semiconductor) with carnauba wax and microscopic silica particles. Using a modified laser printer, they deposit this powder in precise patterns. The laser’s heat briefly melts the mixture, allowing it to reform into a layered structure.
a) Schematic of the ball milling process for the synthesis of perovskite powders and toner. b) The photograph of the perovskite toner. c) Working principle of laser printing. (Image: Reprinted with permission by Wiley-VCH Verlag)
Detailed microscope analysis revealed why this printing method produces such stable materials. When the laser melts the powder, the wax and silica naturally separate from the perovskite due to their different chemical properties – like oil separating from water. As the material cools, the perovskite forms crystals surrounded by a protective shell of wax and silica. This self-organized structure forms automatically during printing, requiring no additional manufacturing steps.
The researchers subjected their printed materials to conditions that typically destroy perovskites within minutes. The films maintained 90% of their electrical conductivity after exposure to X-ray radiation doses of 200 Gy – equivalent to several years of exposure in low Earth orbit and far beyond what conventional electronics can withstand. Under extreme humidity (90% relative humidity, compared to typical indoor levels of 30-50%), the printed materials showed only minor degradation after five hours, while conventional perovskite films failed completely within minutes. Even at temperatures of 80 °C, hot enough to cause rapid degradation in normal perovskite devices, the printed versions maintained stable performance for over five hours.
The current trade-off for this exceptional stability is reduced electrical performance. The printed materials show about one-tenth the electrical conductivity of conventional perovskite films because the protective wax and silica components act as electrical insulators. However, this lower conductivity still exceeds the minimum requirements for applications like radiation detectors in medical equipment or solar cells for satellites, where reliable long-term operation matters more than maximum efficiency.
The printing process offers several additional advantages over traditional manufacturing methods. It works in normal air at room temperature, unlike conventional techniques that require controlled atmospheres. The printer can deposit materials in precise patterns as small as 30 micrometers, essential for creating complex electronic devices. Most importantly, it eliminates the need for toxic solvents that make traditional perovskite manufacturing hazardous.
This advance provides a practical solution to the stability problems that have limited perovskite applications. By creating inherently stable materials through a straightforward printing process, the research establishes a foundation for developing perovskite devices that can operate reliably in real-world conditions. The method’s compatibility with standard manufacturing equipment and elimination of toxic solvents could accelerate the commercial adoption of perovskite electronics in applications where environmental durability is critical.
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