In the world of modern technology, light-emitting diodes (LEDs) have become a prevalent source of illumination for various devices, from indoor lighting to computer screens and smartphones. While they offer energy efficiency, their manufacturing process remains complex and costly.
To address this limitation, Stanford researchers set out to explore perovskite LEDs, or PeLEDs, a more cost-effective and easier-to-produce alternative. Through their experiments, they managed to enhance the brightness and efficiency of PeLEDs significantly. However, an unexpected setback occurred – the lights began to fizzle out within minutes. This outcome highlighted the intricate trade-offs that must be thoroughly understood when working with these materials.
Dan Congreve, an assistant professor of electrical engineering and the senior author of the research paper published in Device on August 1, emphasized the significance of their progress in comprehending the degradation issue. The crucial question now is whether they can find a way to mitigate the degradation while retaining the improved efficiency. Congreve is hopeful that overcoming this hurdle will pave the way for a viable commercial solution, ultimately revolutionizing the LED industry.
The promises and pitfalls of perovskites
LEDs convert electrical energy into light by passing an electric current through a semiconductor, which emits light when an electric field is applied. However, creating these semiconductors is complicated and expensive compared to less energy-efficient lights like incandescent bulbs and fluorescents.
Traditional LEDs are grown on expensive surfaces like sapphire substrates, costing hundreds of dollars. Perovskite LEDs, or PeLEDs, use a semiconductor called metal halide perovskites, making their production more cost-effective. Engineers can grow perovskite crystals on glass substrates or dissolve them in a solution and apply them like paint on glass, simplifying the manufacturing process.
PeLEDs offer advantages such as energy-efficient indoor lighting and enhanced color purity for smartphone and TV displays. However, they face challenges, as they degrade quickly and may not match the energy efficiency of regular LEDs due to defects in the perovskite's atomic structure, hindering light emission and overall device efficiency.
Shine brighter, fade faster
To tackle the challenges faced by PeLEDs, Fernández built on a technique introduced by Congreve and Gangishetty. They addressed the energy-wasting gaps in perovskites caused by missing lead atoms by substituting 30% of the lead with manganese atoms, resulting in significant improvements. The brightness of PeLEDs more than doubled, efficiency nearly tripled, and their lifespan extended from under a minute to 37 minutes.
To mitigate health risks associated with lead, Fernández further experimented by adding a phosphine oxide called TFPPO into the perovskite. This addition led to even more remarkable results, making the lights up to five times more energy-efficient than using only manganese. However, there was a trade-off; the lights faded to half their peak brightness in just two and a half minutes, while the untreated perovskites maintained their brightness for the full 37 minutes.
While these advancements show promise, further research is needed to strike the right balance between efficiency, brightness, and lifespan for PeLEDs to become a commercially viable and safe lighting solution.
Understanding the trade-off
Fernández believes that the increased obstacles related to charge transport within PeLEDs treated with TFPPO lead to a decrease in efficiency over time compared to untreated PeLEDs. The team also found that while TFPPO initially fills gaps in the perovskite's atomic structure, these gaps reopen quickly, affecting both energy efficiency and durability.
To overcome these challenges, Fernández plans to experiment with different phosphine oxide additives to understand their effects better and find ways to improve stability while maintaining high efficiency.
Meanwhile, Congreve's lab is working on addressing other limitations of PeLEDs, like their difficulty in producing violet and ultraviolet light. In recent research led by Ph.D. student Manchen Hu, they discovered that adding water to the solution during perovskite crystal formation resulted in PeLEDs emitting bright violet light five times more efficiently.
With ongoing advancements, ultraviolet PeLEDs could find applications in sterilizing medical equipment, water purification, and indoor crop growth, offering more affordable solutions than current LED technologies allow.
Source: Stanford University