Low-temperature solution-processed wavelength-tunable perovskites for lasing. Guichuan Xing, Nripan Mathews, Swee Sien Lim, Natalia Yantara, Xinfeng Liu, Dharani Sabba, Michael Grätzel, Subodh Mhaisalkar, Tze Chien Sum. 2014. Nature Materials, in press. https://hdl.handle.net/10356/79520. https://doi.org/10.1038/nmat3911. The study presents low-temperature solution-processed wavelength-tunable perovskites for lasing. The perovskite material, CH3NH3PbI3, was spin-coated to form a 65 nm thick film with strong absorbance from UV to near-infrared (800 nm), with two distinct peaks at 480 nm and 760 nm. The material exhibits strong photoluminescence (PL) at 770 nm. The room temperature PL quantum yield was measured using an integrating sphere. The material's gain was assessed using Variable Stripe Length (VSL) measurements, showing a gain spectrum. The material also exhibited lasing from single crystals, with a full width half maximum of 1.2 nm for the most prominent mode. The trap states density in the perovskite thin films was determined using differential equations, revealing two types of traps: bulk (surface/interfacial) traps with fast (slow) trapping times. The bulk trap density was found to be ~5 × 10^16 cm^-3, while the surface/interfacial trap density was ~1.6 × 10^17 cm^-3. The trap density was correlated with a simple estimation of the total trap density. Finite difference time domain (FDTD) simulations were performed to evaluate the optical confinement effects of the PCBM layer. The simulations showed that the PCBM layer improved light confinement in the perovskite film. The out-of-plane polarized component exhibited poor confinement within the perovskite film. Temperature-dependent studies showed that the perovskite material undergoes a phase transition from tetragonal to orthorhombic around 160 K, which is clearly manifested as a modulation of the PL spectra. The emission peak energies decreased slightly with decreasing temperatures. The ASE threshold was found to be almost temperature-insensitive, similar to organic chromophores and quantum dots. The temperature-insensitivity of the ASE threshold stems from the extremely low trap states density and almost temperature-invariant charge carrier diffusion. The study also demonstrated lasing from the perovskite material in a solar cell configuration and on flexible substrates. The ASE photostability was measured under ambient conditions, showing good performance. The results indicate that low-temperature solution-processedLow-temperature solution-processed wavelength-tunable perovskites for lasing. Guichuan Xing, Nripan Mathews, Swee Sien Lim, Natalia Yantara, Xinfeng Liu, Dharani Sabba, Michael Grätzel, Subodh Mhaisalkar, Tze Chien Sum. 2014. Nature Materials, in press. https://hdl.handle.net/10356/79520. https://doi.org/10.1038/nmat3911. The study presents low-temperature solution-processed wavelength-tunable perovskites for lasing. The perovskite material, CH3NH3PbI3, was spin-coated to form a 65 nm thick film with strong absorbance from UV to near-infrared (800 nm), with two distinct peaks at 480 nm and 760 nm. The material exhibits strong photoluminescence (PL) at 770 nm. The room temperature PL quantum yield was measured using an integrating sphere. The material's gain was assessed using Variable Stripe Length (VSL) measurements, showing a gain spectrum. The material also exhibited lasing from single crystals, with a full width half maximum of 1.2 nm for the most prominent mode. The trap states density in the perovskite thin films was determined using differential equations, revealing two types of traps: bulk (surface/interfacial) traps with fast (slow) trapping times. The bulk trap density was found to be ~5 × 10^16 cm^-3, while the surface/interfacial trap density was ~1.6 × 10^17 cm^-3. The trap density was correlated with a simple estimation of the total trap density. Finite difference time domain (FDTD) simulations were performed to evaluate the optical confinement effects of the PCBM layer. The simulations showed that the PCBM layer improved light confinement in the perovskite film. The out-of-plane polarized component exhibited poor confinement within the perovskite film. Temperature-dependent studies showed that the perovskite material undergoes a phase transition from tetragonal to orthorhombic around 160 K, which is clearly manifested as a modulation of the PL spectra. The emission peak energies decreased slightly with decreasing temperatures. The ASE threshold was found to be almost temperature-insensitive, similar to organic chromophores and quantum dots. The temperature-insensitivity of the ASE threshold stems from the extremely low trap states density and almost temperature-invariant charge carrier diffusion. The study also demonstrated lasing from the perovskite material in a solar cell configuration and on flexible substrates. The ASE photostability was measured under ambient conditions, showing good performance. The results indicate that low-temperature solution-processed