Organic-inorganic halide perovskite semiconductors with the attractive physics properties, including strong photoluminescence (PL), huge oscillator strengths, and low nonradiative recombination losses, are ideal candidates for studying the light-matter interaction in nanostructures. Here, we demonstrate the coupling of the exciton state and the cavity mode in the lead halide perovskite microcavity system at room temperature. The Purcell effect in the coupling system is clearly observed by using angle-resolved photoluminescence spectra. Kinetic analysis based on time-resolved PL reveals that the spontaneous emission rate of the halide perovskite semiconductor is significantly enhanced at resonance of the exciton energy and the cavity mode. Our results provide the way for developing electrically driven organic polariton lasers, optical devices, and on-chip coherent quantum light sources.

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The time evolution of the current–voltage characteristic of planar heterojunction perovskite solar cell (PSC) is studied within an operating temperature range of 200–325 K. The photovoltaic (PV) performance of PSC is found to be influenced by five carrier transport pathways, which strongly depend on operating temperature and light illumination. At low temperature, a severe degradation of PV performance is presented but temporary. This is attributed to ion accumulation at the TiO2/CH3NH3PbI3 and hole transport material/CH3NH3PbI3 interfacial regions, as an origin of screening effect of built‐in field, evidenced by the low external quantum efficiency (EQE). By light illumination at open‐circuit, a steady PV performance will be reached and the stabilization time increases with decreasing temperature. The recovery of PV performance is attributed to ion diffusion in CH3NH3PbI3 layer in the absence of electric field. The EQE observations indicate that photogenerated carriers are separated and collected efficiently after a long time light illumination due to a reduction of the screening effect. At high temperature, because of the low ion density at interfacial regions, the PV performance shows a quick response to light. These findings may help understanding of the mechanism of temperature‐dependent photogenerated carrier transport in the PSC.

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In recent years, perovskite solar cell (PSC) has achieved power conversion efficiency as high as over 20 %, making it competitive with high-efficiency thin film solar cells such as CuInGaSe and CdTe solar cells. However, the critical issue of reliability and stability for PSC should be addressed since a significant degradation of photovoltaic (PV) performance at low temperature has been found regardless of planar mesoporous PSC. To reveal the degradation of PV performance in PSC, the temperature-dependent PV performance of the planar PSC is investigated in detail. A PSC sample is loaded into a cryostat chamber connected to a compressor and illuminated by a halogen lamp. The operating temperature varies from 200 K to 325 K and the current-voltage (J-V) characteristic of planar PSC is measured at different scan rates from 10 V/s to 0.0017 V/s. At a fast scan rate of 10 V/s, the PSC shows a low PV performance at either low temperature or high temperature. The short-circuit current (JSC), open-circuit voltage (VOC) and maximum power point (PMPP) are found to decline with the temperature decrteasing. Moreover, the J-V curve also shows the S-shape characteristic. This suggests that the inefficient transport of photo-generated carriers occurs in the PSC. Ions such as Pb2+, CH3NH3+ and I-vacancies cause the screening effect of built-in field and the photo-generated carriers cannot be separated nor collected efficiently. As a result, JSC and VOC show small values in J-V curves measured at a fast scan rate. However, the degradation in PV performance is temporary. The PV performance gradually reaches a steady state at different operating temperatures with scan rate going down to 0.0017 V/s. The PMPP and VOC increase with temperature decreasing. These results indicate that a long illumination time is necessary for PSC to reach a steady state. After long-time illumination under biased condition (i.e., J-V curves measured at slow scan rate), the built-in field is compensated for by the external bias and the ions piling in the interface regions have enough time to diffuse towards the opposite direction. Thus, the screening effect of built-in field is reduced and the PV performance of PSC reaches a steady state. According to the result of device simulation, the increasing VOC at low temperature is attributed to the enhanced built-in potential difference and the reduced recombination rate of carriers. The temperature-dependent external quantum efficiency measurements of planar PSC before and after light illuminationis are performed to investigate the mechanism of carrier transport. It reveals that the separation and collection efficiencies of photo-generated carriers can be improved significantly after light illumination due to the fact that the screening effect of built-in field is reduced. These findings help understand the carrier transport mechanism in planar PSC.

Er-Tm codoped ZnO thin film is synthesized by co-sputtering from separated Er, Tm, and ZnO targets. A flat and broad emission band is achieved in a range of 1400-2100 nm by optimizing annealing temperature, and the observed 1460, 1540, 1640 and 1740 nm emission bands are attributed to the transitions of Tm3+: 3H4 →3F4, Er3+ 4I13/2 →4I15/2, Tm3+ 1G4 → 3F2 and Tm3+ 3F4 → 3H6 transitions, respectively, which cover S, C, L, U bands. The intensity ratios of 1640 to 1535 nm and 1740 to 1535 nm below 1000 ℃ are nearly constant, while the ratios increase sharply above 1000 ℃. The temperature dependence of photoluminescence (PL) spectrum is studied under 10-300 K. With increasing the operation temperature, the bandwidth of broadband is nearly invariable (340-360 nm), and the Tm3+ PL emission intensities of 1640 nm and 1740 nm from Er-Tm co-doped ZnO thin film decrease by a factor of 1.5 and 2, respectively. Moreover, the 1535 nm emission intensity is increased by a factor of 1.2. This phenomenon is attributed to the complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and the increase of phonon-assisted ET rate with temperature as well. And the cross relaxation between Tm3+ ions does not occur.