Effects of bendable P3CT polymers layer on the photovoltaic performance of perovskite solar cells.

We report on the formation of bendable and edge-on poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT) polymers thin layer used as a hole modification layer (HML) in the inverted perovskite solar cell. The aggregations of 2D layer-like P3CT polymers in dimethylformamide (DMF) solution can be formed via aromaticπ-πstacking interactions and/or hydrogen-bonding interactions with the different concentration from 0.01 to 0.02 wt%, which highly influences the photovoltaic performance of the inverted perovskite solar cells. The atomic-force microscopic images and water droplet contact angle images show that the P3CT polymers modify the surface properties of the transparent conductive substrate and thereby dominating the formation of perovskite crystalline thin films, which play important roles in the highly efficient and stable perovskite solar cells. It is noted that theVOC(JSC) of the encapsulated solar cells values are maintained to be higher than 1.115 V (22 mA cm-2) after 104 d when an optimizedπ-πstacked and hydrogen-bonded P3CT polymer is used as the HML. On the other hand, the solar cell showed a high long-term stability by maintaining 85% of the initial power conversion efficiency in the ambient air for 103 d.

Improving the photovoltaic performance of inverted perovskite solar cells via manipulating the molecular packing structure of PCBM.

In this study, the molecular packing structure of solution-processed phenyl-C61-butyric acid methyl ester (PCBM) thin film was manipulated by varying the volume ratio of chlorobenzene (CB) to bromobenzene (BrB) from 100:0 to 50:50, which largely influences the device performance of the PCBM/perovskite heterojunction solar cells. Absorbance spectra, photoluminescence spectra, atomic force microscopic images and contact angle images were used to investigate the molecular packing structure effects of the PCBM thin films on the device performance of the inverted perovskite solar cells. Our experimental results show that the formation of PCBM aggregates and the contact quality at the PCBM/perovksite interface significantly influence the open-circuit voltage, short-circuit current density and fill factor of the resultant solar cells simultaneously. It is noted that the PCE of the encapsulated inverted CH3NH3PbI3(MAPbI3) solar cells exhibited a stable and high power conversion efficiency of 18%.

Understanding the PEDOT:PSS, PTAA and P3CT-X Hole-Transport-Layer-Based Inverted Perovskite Solar Cells.

The power conversion efficiencies (PCEs) of metal-oxide-based regular perovskite solar cells have been higher than 25% for more than 2 years. Up to now, the PCEs of polymer-based inverted perovskite solar cells are widely lower than 23%. PEDOT:PSS thin films, modified PTAA thin films and P3CT thin films are widely used as the hole transport layer or hole modification layer of the highlyefficient inverted perovskite solar cells. Compared with regular perovskite solar cells, polymer-based inverted perovskite solar cells can be fabricated under relatively low temperatures. However, the intrinsic characteristics of carrier transportation in the two types of solar cells are different, which limits the photovoltaic performance of inverted perovskite solar cells. Thanks to the low activation energies for the formation of high-quality perovskite crystalline thin films, it is possible to manipulate the optoelectronic properties by controlling the crystal orientation with the different polymer-modified ITO/glass substrates. To achieve the higher PCE, the effects of polymer-modified ITO/glass substrates on the optoelectronic properties and the formation of perovskite crystalline thin films have to be completely understood simultaneously.

Long-time measurements of line-integrated plasma electron density using a two-color homodyne optical fiber interferometer.

A two-color homodyne Mach-Zehnder (M-Z) optical fiber interferometer with wavelengths of 1.55 and 1.31 µm was developed for long-time measurement of line-integrated plasma electron density. A novel phase difference demodulation algorithm based on a single 3 × 3 optical coupler was implemented in a two-color optical fiber interferometer scheme for the first time. Our laboratory tests showed that this new optical fiber interferometer could determine the phase shift due to the low-frequency ambient vibration and could maintain high phase resolution measurement. The resolution of the new interferometer was less than 0.04 rad in 1000 s, corresponding to a line-averaged electron density of less than 1.0 × 1019 m-2. Actual plasma discharge experiments performed on KTX-CTI, which is a new compact torus injector (CTI) constructed at the Keda Torus eXperiment (KTX), showed that this interferometer has excellent several-second stability.

Improvement of interfacial contact for efficient PCBM/MAPbI3planar heterojunction solar cells with a binary antisolvent mixture treatment.

Atomic-force microscopic images, x-ray diffraction patterns, Urbach energies and photoluminescence quenching experiments show that the interfacial contact quality between the hydrophobic [6,6]-phenyl-C61-buttric acid methyl ester (PCBM) thin film and hydrophilic CH3NH3PbI3(MAPbI3) thin film can be effectively improved by using a binary antisolvent mixture (toluene:dichloromethane or chlorobenzene:dichloromethane) in the anti-solvent mixture-mediated nucleation process, which increases the averaged power conversion efficiency of the resultant PEDOT:PSS (P3CT-Na) thin film based MAPbI3solar cells from 13.18% (18.52%) to 13.80% (19.55%). Beside, the use of 10% dichloromethane (DCM) in the binary antisolvent mixture results in a nano-textured MAPbI3thin film with multicrystalline micrometer-sized grains and thereby increasing the short-circuit current density and fill factor (FF) of the resultant solar cells. It is noted that a remarkable FF of 80.33% is achieved, which can be used to explain the stable photovoltaic performance without additional encapsulations.

Efficiency improvement of P3CT-Na based MAPbI3solar cells with a simple wetting process.

The averaged power conversion efficiency of polyelectrolytes (P3CT-Na) based MAPbI3solar cells can be increased from 14.94% to 17.46% with a wetting method before the spin-coating process of MAPbI3precursor solutions. The effects of the wetting process on the surface, structural, optical and excitonic properties of MAPbI3thin films are investigated by using the atomic-force microscopic images, x-ray diffraction patterns, transmittance spectra, photoluminescence spectra and Raman scattering spectra. The experimental results show that the wetting process of MAPbI3precursor solution on top of the P3CT-Na/ITO/glass substrate can be used to manipulate the molecular packing structure of the P3CT-Na thin film, which determines the formation of MAPbI3thin films.

In situ detection of hydroxyl radicals in mitochondrial oxidative stress with a nanopipette electrode.

A novel nanopipette electrode was facilely constructed for the detection of ˙OH based on the inner surface wettability. The nanopipettes with excellent analytical performance were empolyed for in situ detection of ˙OH changes induced by mitochondrial oxidative stress and further utilized to study the association of ˙OH with Alzheimer's disease.

Optical fiber interferometer application for high electron density measurements on compact torus plasmas.

An optical fiber Mach-Zehnder interferometer at a wavelength of 1.55 µm has been developed for measurements of high electron density on compact torus (CT) plasmas with a high time resolution of 0.1 µs and high phase resolution of 6.4 × 10-4 rad. To improve density measurement accuracy, the phase noise of the interferometer has been investigated in detail and optimized. In the bench test, the interferometer was calibrated using a piezoelectric ceramic actuator with known stroke. Initial results on CT plasma show that the optical fiber interferometer provides reliable density measurements at two spatial locations and the bulk velocity of plasma can be determined by the method of time of flight.

Origins of the s-shape characteristic in J-V curve of inverted-type perovskite solar cells.

Fullerene derivative thin films have been widely used in inverted-type perovskite solar cells as the electron transport layer (ETL) and hole blocking layer. However, the smooth contact at the interface between the hydrophobic [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and hydrophilic CH3NH3PbI3 (MAPbI3) thin film has not yet been completely understood. The contact at the PCBM/MAPbI3 interface strongly influences the photovoltaic performance. The photovoltaic devices were characterized by measuring the light intensity-dependent current density-voltage (J-V) curves and impedance spectra, which show that the contact at the PCBM/MAPbI3 interface simultaneously influences the shunt resistance (carrier recombination) and series resistance (interfacial contact). In addition, x-ray diffraction patterns, atomic force microscopic images, absorbance spectra and photoluminescence spectra were used to explore the contact at the PCBM/MAPbI3 interface. The experimental results show that the flat MAPbI3 thin film cannot be completely covered by a PCBM thin film and thereby results in the s-shape characteristic in the J-V curve of the resultant solar cells. The s-shaped J-V curve can be suppressed by increasing the crystallinity and surface roughness of the MAPbI3 thin film. With the use of an interface modification layer in between the PCBM thin film and Ag cathode, the power conversion efficiency of MAPbI3 solar cells can be increased from 10.50% to 13.71%.

The Way to Pursue Truly High-Performance Perovskite Solar Cells.

The power conversion efficiency (PCE) of single-junction solar cells was theoretically predicted to be limited by the Shockley-Queisser limit due to the intrinsic potential loss of the photo-excited electrons in the light absorbing materials. Up to now, the optimized GaAs solar cell has the highest PCE of 29.1%, which is close to the theoretical limit of ~33%. To pursue the perfect photovoltaic performance, it is necessary to extend the lifetimes of the photo-excited carriers (hot electrons and hot holes) and to collect the hot carriers without potential loss. Thanks to the long-lived hot carriers in perovskite crystal materials, it is possible to completely convert the photon energy to electrical power when the hot electrons and hot holes can freely transport in the quantized energy levels of the electron transport layer and hole transport layer, respectively. In order to achieve the ideal PCE, the interactions between photo-excited carriers and phonons in perovskite solar cells has to be completely understood.

A parametric method for correcting polluted plasma current signal and its application on Keda Torus eXperiment.

We have developed a parametric method for eliminating the background component of the plasma current, which is measured by a Rogowski coil and polluted by the toroidal magnetic field in the vacuum vessel of the Keda Torus eXperiment (KTX) reversed field pinch (RFP) device. The method considers the toroidal magnetic field windings, the KTX vacuum chamber, and the Rogowski coil as a linear time-invariant system; in this case, a constant frequency response function characterizes the system. Using this response function, the current component caused by pollution from the toroidal magnetic field can be predicted exactly for an arbitrary input current to the toroidal magnetic field windings. Compared with the traditional proportional compensation method, the proposed method has great flexibility and universality and it is potentially applicable to cases in which the toroidal field current signal changes over time with plasma feedback signals. Furthermore, the method can be applied to other similarly affected signals, such as magnetic field signals. As an example, we have corrected the poloidal and toroidal magnetic field signals better to reveal the true physical processes for the RFP state.

Highly efficient and stable semi-transparent perovskite solar modules with a trilayer anode electrode.

Highly efficient and stable semi-transparent CH3NH3PbI3 perovskite photovoltaic cells are realized by using an ITO/MoOx bilayer conductive oxide as the anode electrode with a cyclopenta[2,1-b;3,4-b']dithiophene (CT) based hole-transport material (HTM), which allows bifacial illumination from both sides of the electrodes. The wide bandgap MoOx thin film is not only to be an electron blocking layer, but also to be a passivation layer which can withstand the excessive energy bombardment during the magnetron sputtering process for the deposition of a high-quality ITO thin film. Atomic-force microscopy images, transmittance spectra and water-droplet contact angle images show that the interfacial contact between MoOx and hole transport layer (HTL) strongly influences the short-circuit current density (JSC) and fill factor (FF). The highest power conversion efficiency (PCE) values for the bifacial perovskite solar cells (0.16 cm2) and modules (11.7 cm2) are 16.38% and 14.96%, respectively. In addition, the PCE of the ITO/MoOx/CT-HTM based perovskite solar module decreases slowly toward a stable value (∼11%) for more than 700 h under wet environment conditions (70 ± 5 RH%).

Annealing Effect on (FAPbI3)1-x(MAPbBr3)x Perovskite Films in Inverted-Type Perovskite Solar Cells.

This study determines the effects of annealing treatment on the structure and the optical and electronic behaviors of the mixed (FAPbI3)1-x(MAPbBr3)x perovskite system. The experimental results reveal that (FAPbI3)1-x(MAPbBr3)x (x ~ 0.2) is an effective light-absorbing material for use in inverted planar perovskite solar cells owing to its large absorbance and tunable band gap. Therefore, good band-matching between the (FAPbI3)1-x(MAPbBr3)x and C60 in photovoltaic devices can be controlled by annealing at various temperatures. Accordingly, an inverted mixed perovskite solar cell with a record efficiency of 12.0% under AM1.5G irradiation is realized.