Hybrid lead halide perovskites exhibit carrier properties that resemble those of pristine nonpolar semiconductors despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. Here, we reveal the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: CH3NH3PbBr3, CH(NH2)2PbBr3, and CsPbBr3. We observed hot fluorescence emission from energetic carriers with ~102-picosecond lifetimes in CH3NH3PbBr3 or CH(NH2)2PbBr3, but not in CsPbBr3. The hot fluorescence is correlated with liquid-like molecular reorientational motions, suggesting that dynamic screening protects energetic carriers via solvation or large polaron formation on time scales competitive with that of ultrafast cooling. Similar protections likely exist for band-edge carriers. The long-lived energetic carriers may enable hot-carrier solar cells with efficiencies exceeding the Shockley-Queisser limit.

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Screening in crystalline liquids protects energetic carriers in hybrid perovskites

A review of Sb2Se3 photovoltaic absorber materials and thin-film solar cells

Structured Light from Lasers

Development of high-performance fiber-shaped wearable sensors is of great significance for next-generation smart textiles for real-time and out-of-clinic health monitoring. The previous focus has been mainly on monitoring physical parameters such as pressure and strains associated with human activities. Development of an enzyme-based non-invasive wearable electrochemical sensor to monitor biochemical vital signs of health such as the glucose level in sweat has attracted increasing attention recently, due to the unmet clinical needs for the diabetic patients. To achieve this, the key challenge lies in the design of a highly stretchable fiber with high conductivity, facile enzyme immobilization, and strain-insensitive properties. Herein, we demonstrate an elastic gold fiber-based three-electrode electrochemical platform that can meet the aforementioned criteria toward wearable textile glucose biosensing. The gold fiber could be functionalized with Prussian blue and glucose oxidase to obtain the working electrode and modified by Ag/AgCl to serve as the reference electrode; and the nonmodified gold fiber could serve as the counter electrode. The as-fabricated textile glucose biosensors achieved a linear range of 0-500 μM and a sensitivity of 11.7 μA mM-1 cm-2. Importantly, such sensing performance could be maintained even under a large strain of 200%, indicating the potential applications in real-world wearable biochemical diagnostics from human sweat.

Highly stretchable and strain-insensitive fiber-based wearable electrochemical biosensor to monitor glucose in the sweat

As star material, perovskites have been widely used in the fields of optics, photovoltaics, electronics, magnetics, catalysis, sensing, etc. However, some inherent shortcomings, such as low efficiency (power conversion efficiency, external quantum efficiency, etc.) and poor stability (against water, oxygen, ultraviolet light, etc.), limit their practical applications. Downsizing the materials into nanostructures and incorporating rare earth (RE) ions are effective means to improve their properties and broaden their applications. This review will systematically summarize the key points in the design, synthesis, property improvements and application expansion of RE-containing (including both RE-based and RE-doped) halide and oxide perovskite nanomaterials (PNMs). The critical factors of incorporating RE elements into different perovskite structures and the rational design of functional materials will be discussed in detail. The advantages and disadvantages of different synthesis methods for PNMs will be reviewed. This paper will also summarize some practical experiences in selecting suitable RE elements and designing multi-functional materials according to the mechanisms and principles of REs promoting the properties of perovskites. At the end of this review, we will provide an outlook on the opportunities and challenges of RE-containing PNMs in various fields.

Rare-earth-containing perovskite nanomaterials: design, synthesis, properties and applications

We thoroughly investigated the carrier-phonon relaxation process in 2D halide perovskites with the general formula of (BA)2(MA)n-1PbnI3n+1, where n = 2, 3, and 4, by femtosecond transient absorption spectroscopy. A significant enhancement of the hot phonon bottleneck effect is observed in the natural multiple quantum well with n = 2 and 3. Specifically, the sample with n = 3 shows a 1000 ps hot carrier relaxation time to reach room temperature, which is 10 times longer compared with its three-dimensional counterpart. We believe that both the organic cation and quantum confinement effect are responsible for this phenomenon. The acoustic phonon cannot propagate due to the decrease in group velocity caused by the confinement effect in such a quantum well structure. In addition, the confined acoustic phonons can up-convert to optical phonons due to the presence of a “hybrid phonon” induced by the organic cation. This result suggests a promising way to obtain long-live hot carrier materials.

Observation of enhanced hot phonon bottleneck effect in 2D perovskites

Enhancing the efficiency of Sb2S3 solar cells using dual-functional potassium doping

Effect of film thickness and bottom electrode material on the ferroelectric and photovoltaic properties of sputtered polycrystalline BiFeO3 films

Piezoelectric and ferroelectric properties of Ba0.9Ca0.1Ti0.9Sn0.1O3 lead-free ceramics with La2O3 addition

Lead-free Ba0.90Ca0.10Ti0.90Sn0.10O3-xY2O3 (BCTSY, x = 0–0.09) ceramics were prepared by traditional solid-state sintering method. All the BCTSY samples showed pure perovskite structures without detectable impurity. Orthorhombic/tetragonal phase coexisted in the sample of x = 0.03 to 0.07. Remarkable enhancement of the electric properties were achieved at x = 0.03 with d33 of 650 pC/N, Kp of 59.6%, and the remnant polarization Pr of 10.2 μC/cm2. The strengthened temperature stability of piezoelectricity is beneficial to the application of the piezoceramics.

Jianhua Qiu

Papers

Observation of enhanced hot phonon bottleneck effect in 2D perovskites

Enhancing the efficiency of Sb2S3 solar cells using dual-functional potassium doping

Effect of film thickness and bottom electrode material on the ferroelectric and photovoltaic properties of sputtered polycrystalline BiFeO3 films

Piezoelectric and ferroelectric properties of Ba0.9Ca0.1Ti0.9Sn0.1O3 lead-free ceramics with La2O3 addition

Y2O3 doped Ba0.9Ca0.1Ti0.9Sn0.1O3 ceramics with improved piezoelectric properties