Lead-Free Perovskite Sensor Detects Ammonia Leaks at Just 1 ppm

A team led by Myungkwan Song of the Energy Environment Materials Research Division at the Korea Institute of Materials Science (KIMS) has developed an ultrasensitive ammonia gas sensor using an environmentally friendly, lead-free perovskite (a crystal-structured material used in sensors and solar cells). The study, published in Small Structures, included Professor Hyung Woo Lee (Pusan National University), Professor Youngho Kang (Incheon National University) and Professor Jincheol Kim (Macquarie University, Australia).

Ammonia has drawn attention as a hydrogen carrier because it helps store and transport hydrogen, otherwise difficult to handle. Even small leaks can harm health, so high-performance sensors are needed at storage, transport and industrial sites. Conventional perovskite gas sensors are highly sensitive, but most contain lead, which harms health and the environment and limits commercial use.

The researchers built a lead-free perovskite based on antimony, called formamidinium antimony bromide (FA3Sb2Br9), as the sensing material. It detected ammonia at concentrations as low as 1 ppm (parts per million). At 100 ppm, it responded within 13 seconds and its electrical signal rose by 235%. It showed far weaker responses to methane, carbon monoxide, nitrogen oxides, hydrogen and methanol, confirming strong selectivity for ammonia. After two months of storage it retained about 97% of its original performance and can be made by simple spin-coating for large-area, low-cost production.

The team also identified a new sensing mechanism. Earlier work attributed the sensor's signal to ammonia molecules adsorbing onto its surface, but the researchers found ammonia instead reversibly intercalates into the perovskite and triggers p-type doping (a process that increases positive charge carriers in a material), raising conductivity and generating the signal. "This study is significant not only because we developed a highly sensitive ammonia sensor using an environmentally friendlier, lead-free perovskite, but also because we identified its sensing mechanism at the atomic level," said Song.

Exposure to ammonia at concentrations of only several tens of parts per million can affect worker health.