Improving the Stability and Optical Properties of Perovskite Films

2019-03-03

HONG KONG, Feb. 14, 2019 — A new approach to producing all-inorganic perovskite films — the result of a joint research effort by City University of Hong Kong (CityU) and Shanghai University — could further the development of high-color-purity, low-cost perovskite LEDs with a high operational lifetime.

The researchers developed an efficient fabrication approach leading to dense, smooth, pinhole-free CsPbBr3 perovskite films with high thermal stability. They introduced trifluoroacetate (TFA) anions to passivate surface defects and control the crystal growth. The interaction of the TFA anions with Pb2+ cations in a CsPbX3 precursor solution significantly improved the crystallization rate of the perovskite films and suppressed surface defects. Using cesium TFA as the cesium source in the one-step solution coating, instead of the commonly used cesium bromide (CsBr), enabled fast crystallization of small-grained CsPbBr3 perovskite crystals, leading to the formation of smooth and pinhole-free perovskite films.

The result was efficient, stable, green perovskite LEDs (PeLEDs) based on inorganic perovskite films, with a high current efficiency of 32.0 cd A-1, corresponding to an external quantum efficiency of 10.5 percent. According to the researchers, their all-inorganic perovskite LEDs demonstrated a record operational lifetime, with a half-lifetime of over 250 hours at an initial luminance of 100 cd/m−2 — a 17 times improvement in operational lifetime compared with CsBr-derived PeLEDs.

PeLEDs potentially offer low manufacturing costs, high-quality light, and energy efficiency. Metal halide (that is, compounds of metals with chlorine, bromine, or iodine) perovskites are a potentially valuable material for solution-processed LEDs, owing to optical properties that include saturated emission colors and easy color tunability.

The researchers say that perovskites based on inorganic cesium cations exhibit better thermal and chemical stability compared to organic-inorganic “hybrid” metal halide perovskites, and could provide the basis for high-performance LEDs with reasonable operational stability. They said that previous inorganic PeLEDs have exhibited relatively poor electroluminescence performance due to their large perovskite grain sizes.

“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,” said professor Andrey Rogach at CityU. “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.”