Lead halide perovskites are surprisingly effective at converting sunlight into electricity, even though they are packed with impurities and structural defects. Its performance is now approaching that of silicon-based solar cells, which have long dominated the industry. In a recent study published in nature communicationsresearchers at the Austrian Institute of Science and Technology (ISTA) have provided a detailed explanation for this unexpected efficiency, solving a mystery that has puzzled scientists for years.
This raises an obvious question. How can a relatively simple, low-cost material compete with the highly refined silicon technology developed over decades? Over the past 15 years, lead halide perovskites have emerged as promising candidates for next-generation solar cells. Unlike silicon, which requires ultra-pure single-crystal wafers, these materials can be manufactured using inexpensive solution-based methods while achieving comparable performance.
ISTA researchers Dmytro Rak and Zhanybek Alpichshev have identified the underlying mechanism behind these unusual properties. Their findings revealed a surprising contrast to traditional solar power technology. While silicon requires near-perfect purity to function efficiently, perovskites benefit from their imperfections. The researchers say a network of naturally occurring structural defects allows charges to travel long distances through the material, which is essential for efficient energy conversion. “Our study provides the first physical description of these materials and explains most, if not all, of their documented properties,” Luck says. This insight could help bring perovskite solar cells closer to widespread use in the real world.
From overlooked materials to breakthroughs in solar power generation
The term “lead halide perovskites” refers to a group of compounds first identified in the 1970s. They are named for their structural similarity to perovskites, a broader class of oxide materials widely studied in materials science. Apart from their ability to form stable organic-inorganic hybrid crystals, they initially attracted little attention and were largely ignored after basic characterization.
Things changed in the early 2010s, when researchers discovered the amazing ability to convert light into electricity. Since then, perovskites have also shown promise in LED and X-ray detection and imaging technologies. “Moreover, these materials exhibit surprising quantum properties, such as quantum coherence at room temperature,” explains Alpikshev, whose research group studies complex phenomena in advanced materials.
How solar cells generate and transport charge
For solar cells to work efficiently, they must absorb sunlight and convert it into an electrical charge. This process produces negatively charged electrons and positively charged “holes.” To produce usable electricity, these charges must travel through the material to reach the electrodes.
This journey is not simple. Charges must travel distances of hundreds of microns, which is equivalent to hundreds of kilometers on the human scale, without becoming trapped or lost along the way.
Silicon-based solar cells address this challenge by eliminating defects that can trap charge before it reaches the electrodes. However, since perovskites are created using solution-based methods, they naturally contain many defects. This makes their strong performance even more amazing. How can charges move efficiently through such defective materials, and why do they remain separated long enough to do so?
Discover the hidden power inside perovskites
One known property of perovskites adds to the mystery. Once an electron and a hole form a bonding pair called an exciton, they tend to recombine quickly. However, experiments have shown that these charges often remain separated within materials for long periods of time.
To explain this contradiction, the ISTA team proposed that internal forces within perovskites actively pull electrons and holes apart, preventing them from recombining. To test this idea, they used nonlinear optical techniques to inject charges deep inside the material. Each time we introduced electrons and holes, we observed a consistent current flowing in the same direction without applying any external voltage. “This observation clearly showed that even deep within the unmodified, as-grown perovskite single crystal, there are internal forces that separate the opposite charges,” Alpikshev says.
Previous research suggested that such behavior does not occur based on the material’s crystal structure. To resolve this contradiction, researchers proposed that the charge separation is not uniform. Instead, it occurs in specific regions known as “domain walls”, where the structure of the material changes slightly. These domain walls form an interconnected network throughout the material.
Visualization of domain walls with silver ions
Verifying the existence of these networks was a major challenge. Most measurement techniques only examine the surface of a material, but domain walls exist deep within.
To overcome this limitation, Luck developed a new approach inspired by his chemistry background. Because perovskites can conduct ions, they investigated whether specific ions could act as markers that reveal their internal structure. He introduced silver ions into the material, which naturally moved and accumulated along the domain walls. These ions were converted to metallic silver, making the network visible under a microscope.
“This qualitative method, invented and implemented at ISTA, is very similar to angiography of biological tissues, except that we are examining the microstructure of the crystals,” says Alpichshev.
Achieving efficient energy flow with charging “highways”
The discovery of a dense network of domain walls throughout perovskites was a turning point. These structures act as channels to channel charge into the material.
As Rack explains: “When an electron-hole pair is generated near a domain wall, the local electric field pulls the electron and hole apart, placing them on opposite sides of the wall. They cannot recombine immediately, and the charge carriers’ time What seems like a few ions on the scale can drift along domain walls and travel long distances.” In fact, these domain walls act as “highways for charge carriers,” enabling the efficient movement of charges and contributing to power generation.
Complete description and future directions
The researchers emphasize that their work provides a unifying explanation for perovskite behavior. “With this comprehensive picture, we are finally able to reconcile many previously contradictory observations about lead halide perovskites and resolve a long-standing debate about the source of perovskites’ superior energy-generating efficiency,” Luck says.
Until now, most efforts to improve perovskite solar cells have focused on tuning their chemical composition, with limited progress. This new understanding opens the door to engineering internal structures instead, potentially increasing efficiency without sacrificing the benefits of low-cost production. The discovery could play a key role in bringing next-generation solar power technology from the lab to the wider world.
