Lead-Free Organic–Perovskite Hybrid Quantum Wells for Highly Stable Light-Emitting Diodes

Two-dimensional
perovskites that could be regarded as natural organic–inorganic
hybrid quantum wells (HQWs) are promising for light-emitting diode
(LED) applications. High photoluminescence quantum efficiencies (approaching
80%) and extremely narrow emission bandwidth (less than 20 nm) have
been demonstrated in their single crystals; however, a reliable electrically
driven LED device has not been realized owing to inefficient charge
injection and extremely poor stability. Furthermore, the use of toxic
lead raises concerns. Here, we report Sn­(II)-based organic–perovskite
HQWs employing molecularly tailored organic semiconducting barrier
layers for efficient and stable LEDs. Utilizing femtosecond transient
absorption spectroscopy, we demonstrate the energy transfer from organic
barrier to inorganic perovskite emitter occurs faster than the intramolecular
charge transfer in the organic layer. Consequently, this process allows
efficient conversion of lower-energy emission associated with the
organic layer into higher-energy emission from the perovskite layer.
This greatly broadened the candidate pool for the organic layer. Incorporating
a bulky small bandgap organic barrier in the HQW, charge transport
is enhanced and ion migration is greatly suppressed. We demonstrate
a HQW-LED device with pure red emission, a maximum luminance of 3466
cd m–2, a peak external quantum efficiency up to
3.33%, and an operational stability of over 150 h, which are significantly
better than previously reported lead-free perovskite LEDs.