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We have measured the temperature dependence of the reflection and photoluminescence spectra of a lead bromide hybrid material (CH 3 NH 3 PbBr 3 ) using high-quality macroscopic single crystals. Single crystals provide clear and sampleindependent reflection spectra that permit discussion of the properties of the photoexcited carriers. We have found that excitons still exist in CH 3 NH 3 PbBr 3 , even at room temperature. We have also determined the temperature dependence of the exciton resonance energy and the line width.In recent years, lead halide organicinorganic hybrid perovskite materials have attracted considerable attention for photovoltaic applications. 16 The reported power conversion efficiencies (PCE) of the hybrid perovskite-type solar cells with lead iodide materials (CH 3 NH 3 PbI 3¹x Cl x ) are more than 20%. Meanwhile, such materials have been studied from the viewpoint that they form ideal low-dimensional systems and have stable excitons. 812 Even in three-dimensional hybrid materials, the exciton binding energies were reported to be 3750 meV. 13This suggests that stable excitons might exist even at room temperature, and seems to contradict the fact that these materials function as excellent photovoltaic materials, for which dissociation of photoexcited electronhole pairs is necessary to extract the photocurrent.While most studies of the excitonic properties have been performed at low temperatures, solar cells work at room temperature. Therefore, in order to resolve the contradiction stated above, it is important to study the temperature dependence of photoexcited carrier properties in these materials. Recent studies of CH 3 NH 3 PbI 3 indicate that the static dielectric constant shows a rapid increase with increasing temperature, suggesting that this effectively decreases the exciton binding energy. 14,15 Consequently, these results support the view that the excitons dissociate at room temperature in CH 3 NH 3 PbI 3 . In order to clarify the intrinsic properties of these materials, however, such investigations should be performed with high-quality single crystals, which are less affected by defects or impurities. Nevertheless, there are few studies on hybrid perovskite single crystals. 1618In this work, we used high-quality macroscopic single crystals of lead bromide hybrid material (CH 3 NH 3 PbBr 3 ), which has similar properties to CH 3 NH 3 PbI 3 but has a larger band gap (ca. 2.35 eV at room temperature).13 Although CH 3 NH 3 PbBr 3 does not absorb near infrared light, a PCE of more than 10% was reported. 19 The reason why we chose CH 3 NH 3 PbBr 3 is that macroscopic single crystals are more easily synthesized than those of CH 3 NH 3 PbI 3 . Using the single crystals, we have measured the temperature dependence of the reflection and photoluminescence (PL) spectra to discuss the properties of the photoexcited carriers. Our results indicate that excitons still exist in CH 3 NH 3 PbBr 3 , even at room temperature. In addition, we have determined the temperature dependence of the exciton reso...

We have measured photoluminescence spectra in CH3NH3PbBr3 at low temperatures and found a nonlinear emission at the lower energy side of the exciton resonance. Considering that this signal shows a rapid decay, we have assigned it as originating from the exciton–exciton inelastic scattering process called P-emission. The energy difference between this P-emission and the free exciton resonance is 20–30 meV, which is consistent with recent studies of the exciton binding energy.

An enantioselective Friedel–Crafts alkylation reaction of pyrroles and indoles with N‐unprotected trifluoromethyl ketimines by use of chiral phosphoric acid provided α‐trifluoromethylated primary amines bearing chiral tetrasubstituted carbon centers in high yields and with high to excellent enantioselectivities. The present reaction is unique to N‐unprotected trifluoromethyl ketimines. No reaction took place with N‐p‐methoxyphenyl (PMP)‐substituted ketimine. Corresponding α‐trifluoromethylated amines were transformed without loss of enantioselectivity.

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