A recent joint-research co-led by City University of Hong Kong (CityU) and Shanghai University has developed an efficient fabrication approach for all-inorganic perovskite films with better optical properties and stability, enabling the development of high color-purity and low-cost perovskite LEDs with a high operational lifetime.
The team has found that using cesium trifluoroacetate (TFA) as the cesium source in the one-step solution coating, instead of the commonly used cesium bromide (CsBr), enables fast crystallization of small-grained CsPbBr3 perovskite crystals, forming the smooth and pinhole-free perovskite films. This is because the interaction of TFA- anions with Pb2+ cations in the CsPbX3 precursor solution greatly improves the crystallization rate of perovskite films and suppresses surface defects.
As a result, the team has managed to make efficient and stable green PeLEDs based on these films, with a maximum current efficient of 32.0 cd A-1 corresponding to an external quantum efficiency of 10.5% - a level generally considered as satisfactory in existing PeLEDs.
More importantly, the all-inorganic perovskite LEDs based on these films demonstrated a record operational lifetime. They have a half-lifetime of over 250 hours at an initial luminance of 100 cd m-2, which is a 17 times improvement in operational lifetime compared with CsBr-derived PeLED.
"Our study suggests that the high color-purity and low-cost all-inorganic lead halide perovskite films can be developed into highly efficient and stable LEDs via a simple optimization of the grain boundaries," says Andrey Rogach, Chair Professor of Photonics Materials at CityU, who is one of the correspondence authors of the paper.
"I foresee significant application potential of such films, as they are easy to fabricate and can be easily deposited by printing to realize various optoelectronic devices," he adds.