Abstract
The success of metal halide perovskites in photovoltaic and light‐emitting diodes (LEDs) motivates their application as a solid‐state thin‐film laser. Various perovskites have shown optically pumped stimulated emission of lasing and amplified spontaneous emission (ASE), yet the ultimate goal of electrically pumped stimulated emission has not been achieved. As an essential step toward this goal, here, a perovskite diode structure that simultaneously exhibits stable operation at high current density (≈1 kA cm−2) and optically excited ASE (with a threshold of 180 µJ cm−2) is reported. This diode structure achieves an electroluminescence quantum efficiency of 0.8% at 850 A cm−2, which is estimated to be ≈3% of the charge carrier population required to reach ASE in the same device. It is shown that the formation of a large angle waveguide mode and the reduction of parasitic absorption losses are two major design principles for diodes to obtain a positive gain for stimulated emission. In addition to its prospect as a perovskite laser, a new application of electrically pumped ASE is proposed as an ideal perovskite LED architecture allowing 100% external radiation efficiency.
Highlights
Introduction covering electrodesThe nature of thin-film stacks causes difficulty in electrical pumping for many compli-In the last decade, metal halide perovskites have been one of the cated lasing designs with amplification along vertical or random most spotlighted semiconductors for optoelectronics owing to direction, which requires significant modification in the diode structure
While our device consists of a Cs0.05FA0.95Pb(Br0.1I0.9)3 perovskite with an amplified spontaneous emission (ASE) threshold of 140 μJ cm−2, there have been several recent reports for lasing in perovskites, having lower threshold.[5,6b,c] For example, a distributed feedback (DFB) laser recently succeeding in CW operation showed a pulsed lasing threshold of 4.7 μJ cm−2,[6a] corresponding to Nexc = 9.6 × 1017 cm−3 close to what our electrical pumping reaches
The loss of 11% comes from Apara in the guided mode in Figure 3e, which can be further suppressed by further separating the indium tin oxide (ITO) and the perovskite to reach unity ELQE in the future
Summary
Our device structure is based on glass/indium tin oxide (ITO)/polyethylenimine ethoxylated (PEIE)-modified ZnO/ Cs0.05FA0.95Pb(Br0.1I0.9) perovskite/2,2′,7,7′-tetrakis[N,N-di(4methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) doped with Li- and Co-salt/Ag, where FA indicates formamidinium, as shown in Scheme 1. This observation can be mainly attributed to the increased temperature of the device (Figure S4, Supporting Information). The ELQE at high J becomes almost independent of (i) and (ii), and rather limited by other losses such as nonradiative bimolecular recombination and Auger recombination.[11] For example, our AC ELQE of 0.8% at 840 A cm−2 is very similar to the previously reported values of ≈1% at 200–1000 A cm−2 in earlier works, which used efficient LEDs with an order of magnitude higher ELQE (>10%) than ours at low DC current injection. Instead of (iii) and (iv) for forward emission, our device is designed to have an efficient waveguide mode suppressing optical loss, as will be discussed in the latter section for optical modeling
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