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Beside the conventional perovskite precursors with lead halides as lead sources, non-halide lead sources provide additional tools for tuning the properties of perovskite layers, and lead acetate is a promising candidate for non-halide lead sources. In this work, we develop the perovskite precursor with a mixed non-halide lead source by partially replacing lead acetate with lead thiocyanate. Scanning electron microscopy and X-ray diffraction measurements indicate that lead thiocyanate additive can remarkably increase the size of perovskite grains and the crystallization of perovskite layers. And the cross-sectional investigation illustrates that the penetration of perovskite materials into TiO2 porous layers also can be improved by the lead thiocyanate additive. As a consequence, the recombination process and charge extraction process of devices are improved. By optimizing the quantity of lead thiocyanate, the power conversion efficiency of devices is increased from 14.0% to 17.2%, and the stability of devices is elevated simultaneously.

For the perovskite solar cells with formamidinium lead iodide (FAPbI3) as a light harvester, cesium ions (Cs+) can be used to stabilize the perovskite crystal structure of FAPbI3. However, the incorporation of Cs+ ions usually reduces the grain size and degrades the crystallization of FAPbI3 layers, and this is harmful to the photovoltaic performance of solar cells. In this work, we incorporate Cs+ ions into FAPbI3 layers using the interfacial doping method, which is different from the mixed solution doping method in previous reports. Elemental analysis indicates that Cs+ dopants cannot be detected at the outer surfaces of perovskite layers, and the majority of Cs+ dopants should be localized in the vicinity of TiO2/perovskite interfaces, which is remarkably different from the distribution of Cs+ dopants in the perovskite layers prepared using the mixed solution doping method. It is found that interfacial doping method can avoid the blue shift of the light absorption edge and can improve the crystallization of FAPbI3 layers. For the optimized conditions, CsxFA1−xPbI3 solar cells prepared using the interfacial doping method achieve a power conversion efficiency (PCE) of 17.1%, which is better than the PCE of CsxFA1−xPbI3 devices prepared using the mixed solution doping method.

Although two-step methods are convenient for producing perovskite layers in mesoporous perovskite solar cells, they usually lead to intensive recombination for planar perovskite devices based on formamidinium ions. In this study, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was employed as the intermediate layer between TiO2 electron transport layers and formamidinium perovskite layers. SEM images indicate that this PCBM intermediate layers encourage the growth of grains in formamidinium perovskite layers. XRD patterns show that these PCBM layers eliminate the yellow δ-phase, thereby improving crystallization. Via optimizing the concentration of PCBM precursor solutions, the average power conversion efficiency of formamidinium planar devices was promoted from 6.8% to 15.1%. Further, it is also noted that devices with optimized PCBM layers are free from the hysteresis effect. Impedance spectra indicate that this improvement comes from the suppression of recombination processes by the PCBM intermediate layers.

The charge transport behavior of barium fluoride nanocrystals has been investigated by in situ impedance measurement up to 23 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in BaF2 nanocrystals include both F− ions and electrons. Pressure makes both the F− ions diffusion and electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge–discharge processes in the Fm3m and Pnma phases more difficult. The electron conduction plays a dominant role in the transport process. In the Fm3m and Pnma phases, the electron transference number increases with increasing pressure.

PbI2 layers with a mesoporous structure are facilely prepared by spin coating of PbI2 in DMF solution with n-butanol additive, which can improve crystallization and modify the orientation of the MAPbI3 layers produced by an interface reaction. The recombination and charge transfer process are improved in the perovskite solar cells with these harvester layers.

Gallium arsenide (GaAs) exhibits outstanding electron transport properties that are useful for many electronics industries. High pressure is a powerful way to induce dramatic electrical conductivity changes in materials. Herein, we investigated the electrical transport properties of GaAs under high pressure up to 25.0 GPa by in situ alternating-current (AC) impedance spectroscopy measurements, temperature dependent electrical resistivity measurements, and first-principles calculations. The experimental results showed that GaAs undergoes a semiconductor to metal transition at approximately 12.0 GPa, which corresponds to the pressure-induced phase transition of GaAs from a zinc-blende to a Cmcm structure. In addition, the dramatic changes in electrical transport parameters, such as the bulk resistance, relaxation frequency, and resistivity, were observed at 12.0 GPa. First-principles calculations show that the energy bands crossed the Fermi level for the Cmcm phase, at the same time electronic localization began to decreases at 12.0 GPa, leading to the metallization of GaAs.

FA1−xCsxPbI3 solid solution films are prepared as light harvesters for perovskite solar cells by a spray reaction. Cs+ ions can improve the quality of the light harvester film, and the average PCE of devices increases from 11.3% for FAPbI3 to 14.2% for FA0.9Cs0.1PbI3. Moreover, FA0.9Cs0.1PbI3-based devices exhibit remarkable improvement on humidity stability.

Herein, we report the intriguing electrical transport and structural properties of compressed Alq3, which is an extensively used electron transport material in OLEDs. The bulk resistance (Rb) of Alq3 increases with uploading pressure, but drops markedly when the uploading pressure is above 8.6 GPa. In contrast, the grain boundary resistance (Rgb) varies smoothly below 16.4 GPa. With further compression, both Rb and Rgb increase with the amorphization of Alq3. The pressure-induced amorphization is found to be reversible at a low density amorphous state, while it is irreversible at a higher density state. Interestingly, XRD measurements indicate no structural transition at ∼8.0 GPa. The variation of Rb is found to be synchronous with the blue-shift of the Al–oxine deformation mode, which rationalizes the anomalous changes of Rb. The Al–oxine interaction is believed to be also significant in the electrical transport properties of dense Alq3, which provides insight into the correlation between its structural changes and electrical transport properties.

In this paper, we develop high performance poly(3,4-ethylenedioxythiophene) (PEDOT) counter electrodes (CEs) by a vapor deposition method, which gives 6.09% in conversion efficiency for the dye-sensitized solar cell (DSSC) with a thin PEDOT film CE (16 nm in thickness). To increase the quantity of PEDOT deposited on the CEs, we insert an antimony tin oxide (ATO) porous conductive supporting layer to increase the internal deposition area. The conversion efficiency of the DSSC with this PEDOT/ATO composite CE is enhanced to 7.47%.

High-pressure electrical transport properties of VO2 have been investigated by in situ resistivity, Hall-effect, and temperature dependence of resistivity measurements. The electrical transport parameters including resistivity, Hall coefficient, carrier concentration, and mobility varies significantly around 10.4 GPa, which can be attributed to the isostructural phase transition of VO2. Temperature dependence of resistivity indicates that the phase transition is a semiconductor-to-semiconductor transformation, not the pressure-induced metallization as previously reported by Raman and IR experiment observations. The dramatic increase of activation energy at 10.4 GPa indicates an increasingly insulating behavior of VO2 accompanied with the isostructural phase transition. The electrical transport properties, especially the carries transportation under compression open up a new possible basis for optimizing the performance of VO2 based applications under ambient or extreme conditions.