Shizhong Yue

Efficacious engineering on charge extraction for realizing highly efficient perovskite solar cells

Efficient extraction of photogenerated charge carriers is of significance for acquiring a high efficiency for perovskite solar cells. In this paper, a systematic strategy for effectively engineering the charge extraction in inverted structured perovskite solar cells based on methylammonium lead halide perovskite (CH3NH3PbI3−xClx) is presented. Intentionally doping the chlorine element into the perovskite structure is helpful for obtaining a high open circuit voltage. The engineering is carried out by modifying the aluminium cathode with zirconium acetylacetonate, doping the hole transport layer of nickel oxide (NiOx) with copper and using an advanced fluorine doped tin oxide (FTO) substrate. This improves the bandgap alignment of the whole device, and thus, is of great benefit for extracting the charge carriers by promoting the transport rate and reducing the trap states. Consequently, an optimized power conversion efficiency of 20.5% is realized. Insights into how to extract charge carriers efficiently with a minimum energy loss are discussed.

Insights into the Influence of Work Functions of Cathodes on Efficiencies of Perovskite Solar Cells

Though various efforts on modification of electrodes are still undertaken to improve the efficiency of perovskite solar cells, attributing to the large scope of these methods, it is of significance to unveil the working principle systematically. Herein, inverted perovskite solar cells based on indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/CH3 NH3 PbI3 /phenyl-C61-butyric acid methyl ester (PC61 BM)/buffer metal/Al are constructed. Through the choice of different buffer metals to tune work function of the cathode, the contact nature of the active layer with the cathode could be manipulated well. In comparison with the device using Au/Al as the electrode that shows an unfavorable band bending for conducting the excited electrons to the cathode, the one with Ca/Al presents a dramatically improved efficiency over 17.1%, ascribed to the favorable band bending at the interface of the cathode with the active layer. Details for tuning the band bending and the corresponding charge transfer mechanism are given in a systematic manner. Thus, a general guideline for constructing perovskite photovoltaic devices efficiently is provided.

Turning a disadvantage into an advantage: synthesizing high-quality organometallic halide perovskite nanosheet arrays for humidity sensors

Though power conversion efficiencies of perovskite solar cells of over 21% have been reported, the degradation of the performance of these cells in the presence of moisture still inhibits the commercialization of these otherwise promising devices. Herein, we decided to utilize the moisture sensitivity of perovskite materials and fabricate a moisture detector based on high-quality CH3NH3PbI3−xClx nanosheet arrays. The resulting devices present a high sensitivity towards humidity with device resistance significantly dropping from 1.28 × 108 Ω at 30% relative humidity (RH) to 7.39 × 104 Ω at 90% RH and a response even faster than that of the commercial psychrometer. This response was even steeper than those of commercial psychrometers. Moreover, our device showed good reversibility and impressive specificity. Thus, the humidity sensitivity of perovskites, while disadvantageous for solar cell applications, was found to be quite applicable in a new field.

Hybrid silicon nanocone–polymer solar cells based on a transparent top electrode

Instead of using a metal grid line as the top electrode for Si nanocone/PEDOT:PSS hybrid solar cells, herein we utilize a fully covered thin layer of transparent MoO3/Ag/ZnS to efficiently collect photo-generated charge carriers without sacrificing photon absorption. Vertical silicon nanocone (SiNC) arrays with short cone lengths are prepared by a metal-assisted chemical etching technique. Such a unique structure favors the subsequent infiltration of PEDOT:PSS into the nanocone array. In addition to decent antireflection and light trapping properties, which can be attributed to the nanostructure array, the power conversion efficiency (PCE) of the hybrid solar cells reaches 5.12% upon optimizing the length of the nanocone and the thickness of the PEDOT:PSS layer. This paper not only provides an elaborate investigation on Si-based hybrid solar cells, but also gives a universal methodology for the preparation of transparent electrodes for other categories of photoelectric devices.

Cardiac support device (ASD) delivers bone marrow stem cells repetitively to epicardium has promising curative effects in advanced heart failure

Ventricular restraint therapy is a non-transplant surgical option for the management of advanced heart failure (HF). To augment the therapeutic applications, it is hypothesized that ASD shows remarkable capabilities not only in delivering stem cells but also in dilated ventricles. Male SD rats were divided into four groups (n = 6): normal, HF, HF + ASD, and HF + ASD-BMSCs respectively. HF was developed by left anterior descending (LAD) coronary artery ligation in all groups except normal group. Post-infarcted electrocardiography (ECG) and brain natriuretic peptide (BNP) showed abnormal heart function in all model groups and HF + ASD-BMSCs group showed significant improvement as compared to other HF, HF + ASD groups on day 30. Masson’s trichrome staining was used to study the histology, and a large blue fibrotic area has been observed in HF and HF + ASD groups and quantification of fibrosis was assessed. ASD-treated rats showed normal heart rhythm, demonstrated by smooth -ST and asymmetrical T-wave. The mechanical function of the heart such as left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP) and heart rate was brought to normal when treated with ASD-BMSCs. This effect was more prominent than that of ASD therapy alone. In comparison to HF group, the SD rats in HF + ASD-BMBCs group showed a significant decline in BNP levels. So ASD can deliver BMSCs to the cardiomyocytes successfully and broaden the therapeutic efficacy, in comparison to the restraint device alone. An effective methodology to manage the end-stage HF has been proved.

Ultra-thin ZnO film as an electron transport layer for realizing the high efficiency of organic solar cells

To overcome the limits of low charge transport efficiency and high absorption in the UV region of conventional thick ZnO layers in organic solar cells, herein we introduce an ultra-thin ZnO film (4 nm) into PBDTTT-CF:PC70BM bulk heterojunction organic solar cells, as the electron transport layer, and realize a power conversion efficiency of 7.51%, which is dramatically higher than that of a device using general ZnO film (28.1 nm). Various techniques from both steady-state and ultra-fast views reveal that the devices with an ultra-thin ZnO film (less than 10 nm) show a higher built-in potential compared to the device with a 28.1 nm ZnO film. Such an enhancement of the built-in potential could facilitate the photo-generated excitons dissociating into free charge carriers and benefit the transport of charge carriers to the electrode. Thus, we have supplied an efficient electron conducting layer not only for the photovoltaic community but also for other photoelectronic devices.

Highly efficient solar cells based on Cl incorporated tri-cation perovskite materials

Though mixed cation hybrid organic–inorganic perovskite materials are of promise due to the high efficiency and long-term stability of the corresponding devices, a fundamental understanding on the function of the mixed cation system is still unclear. Herein, we systematically investigate the roles of the Cs cation and Cl anion in inverted structure perovskite solar cells based on CsxFA0.2MA0.8−xPb(I1−yCly)3. For the role of Cs, we observe that an appropriate amount of Cs in the film could improve the crystal quality of the film and optimize the energy band alignment of the device, thus reducing non-radiative recombination and promoting the charge transport efficiently. The presence of Cl with a suitable concentration also possesses these functions. More importantly, the two limitations for the application of the devices, hysteresis and performance instability, could also be addressed to some extent. Thus a high power conversion efficiency of 20.31% has been realized and a universal method for constructing highly-efficient perovskite solar cells has been provided.