Di Gao

Herein we describe the mechanism of crystallization of Al³⁺ with amorphous TiO₂ on a TiO₂ film, and found that the resultant Al₂TiO₅ was able to improve the average efficiency of planar perovskite solar cells (PSCs) from 15.4 to 17.2%. The electron lifetime in these Al-PSCs was about 3 times longer than that in unmodified PSCs. The O 1s X-ray photoelectron spectrum of the TiO₂/CH₃NH₃PbI₃ interface indicated that the oxygen vacancy or defect peak decreased by more than 31% on modifying the interface with Al₂TiO₅. The stability of the PSCs was improved substantially: Al-PSCs had still 88% of their initial value after 1440 hours, while the efficiency of the reference PSCs decreased to 68% of their initial value.

A tunnelling contact of polystyrene nanofilm was introduced for the first time at the interface of perovskite/hole transfer layer, leading to a significantly reduced charge recombination. Moreover, such a polymeric contact worked as a hydrophobic encapsulation layer for effectively protecting the perovskite against humidity. The resultant PSCs displayed a peak efficiency of 17.80% (vs. 15.90% of the control cell) and an enhanced stability.

In pursuit of reducing the surface trap states of perovskite as well as enhancing the hole control of dopant-free spiro-OMeTAD, an amino-rich graphene (NGs) was introduced via a facial solution method as an interlayer at the perovskite/HTM interface. A number of characterizations, including photoluminescence and impedance spectroscopy, was conducted to reveal the interfacial effect of the NGs, and it was demonstrated that the amino group facilitated the reduced surface trap of perovskite and that graphene could behave as an efficient hole extraction and transfer pathway through the HTM network. Consequently, a maximum PCE of 14.6% could be obtained, which represented a remarkable improvement of ca. 36% over the control device (10.7%), with the improvement mainly related to the increase of J_SC and FF.

The introduction of Cl into CH3NH3PbI3 precursors is reported to enhance the performance of CH3NH3PbI3 solar cell, which is attributed to the significantly increased diffusion lengths of carriers in CH3NH3Pb(I,Cl)3 solar cell. It has been assumed but never experimentally approved that the defect density in CH3NH3Pb(I,Cl)3 solar cell should be reduced according to the higher carrier lifetime observed from photoluminescence (PL) measurement. We have fabricated CH3NH3Pb(I,Cl)3 solar cell by adding a small amount of Cl source into CH3NH3PbI3 precursor. The performance of CH3NH3Pb(I,Cl)3 solar cell is significantly improved from 15.39% to 18.60%. Results from scanning electron microscopy and X-ray diffraction indicate that the morphologies and crystal structures of CH3NH3PbI3 and CH3NH3Pb(I,Cl)3 thin films remain unchanged. Open circuit voltage decay and admittance spectroscopy characterization jointly approve that Cl plays an extremely important role in suppressing the formation of defects in perovskite solar cells.

A continuous and compact hole-blocking layer is crucial to prevent photocurrent recombination at the photoanode/electrode interface of high-performance mesostructure perovskite-based solar cells. Novel TiO₂/ZnO/TiO₂ sandwich multi-layer compact film prepared as hole-blocking layer for perovskite solar cell. Herein, TiO₂, ZnO, and TiO₂ layers were successfully deposited by spin-coating onto FTO glass substrate in sequence. The fill factor and power conversion efficiency of the perovskite solar cell are remarkably improved by the employment of a TiO₂/ZnO/TiO₂ sandwich compact layer. Perovskite solar cell based on TiO₂/ZnO/TiO₂ sandwich film has been observed to exhibit maximum incident-photon-to-current conversion efficiency in the visible region (400–780 nm) and reach a power conversion efficiency of 12.8% under AM1.5G illumination. Copyright © 2016 John Wiley & Sons, Ltd.

Compared to the fast electron transport in perovskite and rapid electron injection from perovskite to TiO ₂ nanoparticle scaffold, the slower electron transport rate in mesoporous TiO ₂ is reported to be a hindrance factor for power conversion efficiency.

Cl incorporation has been reported to be able to significantly increase the diffusion length of carriers in organo-lead halide perovskite thin films. However, due to the low solubility of PbCl₂, Cl incorporation has been rarely reported in a two-step process, which is capable of producing uniform organo-lead halide perovskite thin films. In this letter, we report a novel growth method that combines the two-step process and Cl incorporation. The Cl-incorporated organo-lead halide perovskite solar cell made from a two-step process demonstrated a power conversion efficiency of 10.5%, which is 27% higher than that without Cl incorporation. Further investigation was performed to explore the fundamentals of the enhancement. Kelvin probe force microscopy (KPFM) measurement revealed a larger band bending at grain boundaries with Cl incorporation, which brings the Fermi level of the bulk perovskite thin film closer to the center of the bandgap. As a result, a p–i–n type of junction is formed in the devices with Cl incorporation, which facilitates the charge carrier collection. Additional carrier lifetime measurements indicate that the electron lifetime in the perovskite thin film with Cl incorporation is longer, indicating reduced recombination in the devices with Cl incorporation.

Cu₂ZnSnS₄ (CZTS) has attracted intensive interest for application in photovoltaic technology due to its excellent semiconductor properties. We report a nanostructured CZTS solar cell which was fabricated by infiltrating of CZTS nanoparticles into CdS coated ZnO nanorod arrays. The well aligned ZnO nanorods facilitate the efficient infiltration of CZTS nanoparticles. A hole transport layer was deposited to facilitate the transport of holes. The nanostructured CZTS solar cell demonstrated a remarkably high short‐circuit current density (11.0 mA/cm²). As a result, a power conversion efficiency of 2.8% was obtained. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The electroencephalography (EEG) is a widely used diagnostic tool for a number of clinical applications, such as diagnosis of epilepsy and study of sleep. Traditionally, to acquire a single channel of EEG signal, at least three electrodes must be installed on the skin separated at certain distances. They must also be connected to an amplifier by electrode leads. These basic requirements are acceptable in most clinical laboratories, but are unacceptable in certain point-of-care applications, such as during patient transportation. In order to remove these requirements, we are designing a single-unit EEG sensor in the size of a U.S. penny. It contains multiple closely spaced dry electrodes that can hook onto the skin, an electronic circuitry for signal amplification, digitization and wireless transmission, and a battery providing power. In this paper, we answer two key questions regarding the feasibility of the single-unit design: 1) can the closely-spaced electrodes obtain EEG signal reliably? and 2) will the electrodes orientated in certain ways improve signal quality? We conducted experiments utilizing closely spaced electrodes to record the alpha wave in the EEG. Our results have shown positive answers to the two feasibility questions.