Can Trihalide Lead Perovskites Support Continuous Wave Lasing?

Abstract

COMMUNICATIONRecent studies have shown amplifi ed spontaneous emission (ASE) under short pulse excitation conditions, with lasing threshold densities comparable to or even lower than those observed in state-of-the-art organic materials. [ 18,19,[30][31][32] Short pulse excitation is a very favorable regime for light amplifi cation, as carrier densities well above the threshold required for lasing can be easily injected. Yet light amplifi cation disappears just a few picoseconds after excitation, a transient regime that is far away from the working conditions of interest for applications. How long light amplifi cation can last in perovskite materials is the open question we address in this Communication.Here, we demonstrate ASE sustained over transients two orders of magnitude longer than the excited state lifetime. Through optical spectroscopy, we measure threshold densities for ASE as a function of the temperature of the environment and the duration of the exciting laser pulse. Particularly, we employ an optical thermometry technique to track the dynamics of the temperature of the electron-hole plasma and identify the runaway heating mechanism limiting the maximum achievable duration of light amplifi cation. We then discuss the conditions needed for true continuous wave operation of light amplifi cation.Light emission in methylammonium lead iodide (MAPbI 3 ) and methylammonium lead bromide (MAPbBr 3 ) thin fi lms has fi rstly been analyzed under 130 fs pulsed laser excitation (392 nm in wavelength), using a streak camera to detect timeresolved photoluminescence and a cooled charge-coupled device (CCD) camera for the time-integrated spectra. The resulting photoluminescence decays, shown in Figure 1 a, had characteristic decay times much longer than the pulse duration, few nanoseconds for MAPbBr 3 , tens of nanoseconds for MAPbI 3 , meaning that such an excitation regime can be considered as impulsive. ASE was demonstrated by a sharp peak (Figure 1 b,c) appearing in the low energy side of the emission spectrum for both fi lms once the excitation laser fl uence reached a threshold value; such a value turned out to be 26 µJ cm −2 per pulse for MAPbI 3 , a factor of two lower than for MAPbBr 3 (54 µJ cm −2 per pulse). The corresponding average excited population densities, as calculated by averaging the laser fl uence times the fi lm absorption coeffi cient over the fi lm thickness, were 4 × 10 18 cm −3 and 7 × 10 18 cm −3 for MAPbI 3 and MAPbBr 3 , respectively (see absorption coeffi cients in the Supporting Information paragraph). Films realized from different solution batches and with different age showed variations in ASE threshold fl uence, mainly due to the different optical losses occurring as a result of different morphology. All samples were therefore stored in vacuum and typically measured within the

Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

“…As a consequence, close packed films of nanocrystals demonstrated ASE in a broad range of wavelengths with thresholds of 3-25 μm/cm 2 under femtosecond excitation. ASE was also obtained with nanosecond pulses, but higher pump fluencies were needed (450 μm/cm 2 ), in agreement with the study performed in [106]. Then, colloidal nanocrystals were incorporated in photonic cavities in order to demonstrate lasing.…”

“…Therefore, HPVKs layers have been successfully applied in a wide range of photonic devices, such as photodetectors [91,92] or light emitting diodes [90,93]. In addition, since HPVKs present a fast carrier formation and long recombination time, they are promising materials to reduce the stimulated emission threshold in active devices [94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109], as it has been nicely reviewed in [90].…”

Strong Quantum Confinement and Fast Photoemission Activation in CH3NH3PbI3 Perovskite Nanocrystals Grown within Periodically Mesostructured Films

“…MAPbI 3 , on the other hand, is an efficient near infrared emitter and presents a lower lasing threshold than MAPbBr 3 . [13] Evidence of precise control of the optical properties of MAPbI 3 over a wide spectral range has been reported from colloidal suspensions attained using a two-step process involving the In order to create a stable solid dispersion of MAPbI 3 quantum dots, we follow a standard one-step procedure that starts by dissolving precursors in N,N-dimethylformamide. [5] The solution is then spin coated onto periodically mesostructured metal oxide, namely, TiO 2 or SiO 2 , films of controlled thickness and open porosity, which have been previously deposited on flat glass substrates by a combination of supramolecular templating and dip-coating.…”

“…MAPbI 3 , on the other hand, is an efficient near infrared emitter and presents a lower lasing threshold than MAPbBr 3 . [13] Evidence of precise control of the optical properties of MAPbI 3 over a wide spectral range has been reported from colloidal suspensions attained using a two-step process involving the …”

Triple cation mixed-halide perovskites for tunable lasers

“…The stability of triiodide perovskites was shown to be excellent [17,23], although hurdles still remain to achieving continuous-wave lasing [24,30]. Photophysical investigations of CH 3 NH 3 PbX 3 with mixed-halides undertaken in the context of bandgap tuning for photovoltaics revealed that the emission wavelength and intensity of the mixed-halide material is highly unstable under illumination [31][32][33].…”