The photoluminescence (PL) intensity is often used as an indicator of the performance of perovskite solar cells and indeed the PL technique is often used for the characterization of these devices and their constituent materials. Herein, a systematic approach is presented to the comparison of the conversion efficiency and the PL intensity of a cell in both open‐circuit (OC) and short‐circuit (SC) conditions and its application to multiple heterogeneous devices. It is shown that the quenching of the PL observed in SC conditions is a good parameter to assess the device efficiency. The authors explain the dependence of the PL quenching ratio between OC and SC on the cell efficiency with a simple model that is also able to estimate the carrier extraction time of a device.

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The structural and electronic properties of the methylammonium lead iodide (MAPbI3, MA = CH3NH3) perovskite are investigated as a function of temperature by transport measurements, in situ x-ray diffraction, and optical emission. Lowering the temperature, a transition from the tetragonal to the orthorhombic phase takes place, around 160 K. Such structural transition, monitored by temperature-dependent in situ x-ray diffraction and optical emission, is followed by an inversion of the temperature dependence of the electrical resistivity from a semiconductor-like dependence to a metal-like one. The temperature for such semiconductor-metal transition, depending both on the applied electric field and on the optical excitation, is always below the phase transition temperature. The results demonstrate that perovskite materials display interesting scenarios in which lattice structural transitions combined with optical or electrical excitation strongly affect transport properties. The consequences of these characteristics are analyzed in fundamental and applied science perspectives.

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Carrier dynamics in polycrystalline Bi2Se3 topological insulator thin films were investigated by femtosecond transient absorption spectroscopy (FTAS) at 77 K, by using an infrared pump photon of 0.62 eV energy and a white supercontinuum probe ranging from the near infrared to ultraviolet regions (0.9–3.5 eV). The Bi2Se3 samples were grown by vapor solid deposition, a quick, inexpensive, and easy-to-control growth technique to obtain films of different thicknesses, endowed with topological properties. FTAS spectra present several absorption bleaching signals, which can be attributed to electronic transitions involving both bulk and surface states present in the complex Bi2Se3 band structure. We observe clear differences in the rise times of several bleaching signals, differences that can be attributed to different band filling dynamics. Fast rise times are observed for transitions only involving bulk states, while a delayed onset of the bleaching signal has been observed for transitions involving surface topological states, which are more efficiently populated by carrier–phonon scattering of bulk electrons and holes, rather than by direct photoexcitation. The observed features shed fresh insights into the properties that allow these materials to be employed as innovative, low-cost, and wide-range photodetectors.