Dazheng Chen

Enhanced efficiency of planar perovskite solar cells via a two-step deposition using DMF as an additive to optimize the crystal growth behavior

The performance of perovskite solar cells (PSCs) is extremely dependent on the morphology and crystallization of the perovskite film. However, the complete conversion of PbI2 to perovskite and controlling the perovskite crystal size as well as its surface morphology are challenging in the conventional two-step sequential deposition method. We herein present a facile method involving the use of a polar solvent additive in an inter-diffusion two-step sequential deposition method to achieve a high-quality perovskite film. The results showed that the addition of a small amount of DMF solvent into the MAI precursor solution could help the complete conversion of PbI2 to perovskite, and at the same time could also reduce the pinholes, improve the film morphology, increase the grain sizes and enhance the film absorption ability. The improved perovskite film quality results in the boosting performance of PSCs. Consequently, an optimized device with power conversion efficiency as high as 19.2% is obtained. This current method provides a highly repeatable route for enhancing the PSC performance with the inter-diffusion sequential solution deposition method.

Performance Comparison of Conventional and Inverted Organic Bulk Heterojunction Solar Cells From Optical and Electrical Aspects

The conventional and inverted organic solar cells (OSC and IOSC) based on the bulk heterojunction structure are investigated from both optical and electrical aspects. When the optical aspect is considered only, with the increase of the active layer thickness, the number of photons absorbed in the active layer and the external quantum efficiency tend to increase with the obvious interference behavior for both OSC and IOSC. However, compared to OSC, IOSC shows a better performance except for the thicknesses around which the interference maxima of OSC are obtained. When the electrical aspect is also considered, an effective area in the active layer will be induced by the charge drift length (L), and only the photons absorbed in this effective area have contribution to the photocurrent. By considering optical and electrical aspects together, OSC and IOSC show different behaviors. Compared to IOSC, OSC performs better for relatively thick active layers. Simultaneously, the optical modulation effect is also investigated by introducing an optical spacer layer. It is found that the optical spacer layer can notably enhance the performance of OSC with thin and thick active layers, while it could only degrade the performance of IOSC with relatively thick active layers.

Performance Enhancement of Planar Heterojunction Perovskite Solar Cells through Tuning the Doping Properties of Hole-Transporting Materials

Chemical doping has been widely used to finely tune the electrical properties of organic hole-transporting materials (HTMs) that find widespread applications in perovskite solar cells (PSCs). Here, to shed light on the precise role of chemical p-doping in affecting the charge-transport properties of HTMs and photovoltaic performance of PSCs, two kinds of representative dopants, including lithium bis(trifluoromethane)sulfonimide (LiTFSI) and two Co(III) complexes tris[2-(1H-pyrazol-1-yl)-4-tert-butylpyridine]cobalt(III)tris[bis(trifluoromethylsulfonyl)imide] (FK209) and tris[2-(1H-pyrazol-1-yl)pyridine]cobalt(III)tris[bis(trifluoromethylsulfonyl)imide] (FK102), are employed as the p-type dopant models to dope the 2,2′,7,7′-tetrakis[N,N-di-p-methoxyphenylamine]-9,9′-spirobifluorene (spiro-OMeTAD) HTM. Both dopants can facilitate the generation of oxidized spiro-OMeTAD radical cation and improve hole mobility. Co-doping of FK209 and LiTFSI is necessary to achieve an optimal doping property and best device performance with power conversion efficiency of 17.8% compared to that of the FK209-doped device (13.5%) and the LiTFSI-doped device (15%). UV–vis absorption, space-charge-limited current measurements, and steady-state and time-resolved photoluminescence measurements have confirmed that with the co-doping of the two kinds of p-dopants in a proper ratio the doped spiro-OMeTAD exhibits a high charge carrier mobility and charge carrier transfer/collection capability.

Efficient inverted polymer solar cells using low-temperature zinc oxide interlayer processed from aqueous solution

In this work, an aqueous solution method that entails processing at low temperatures is utilized to deposit a ZnO interlayer in poly(3hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester-based inverted polymer solar cells (PSCs). The effect of ZnO annealing temperature from 50 to 150°C on PSC performance is systemically studied and it is found that the transition point is approximately 80°C. When the ZnO annealing temperature is higher than 80°C, PSCs show similar current density–voltage (J–V) characteristics and achieve a power conversion efficiency higher than 3.5%. Transmittance spectrum, PL spectrum, and surface morphology studies show that an annealing temperature above 80°C is sufficient for ZnO to achieve a relatively good quality, and that a higher temperature only slightly improves ZnO quality, which is confirmed from statistical results. Furthermore, flexible PSCs based on PET substrates show a comparable power conversion efficiency and good flexibility.

Efficient indium-tin-oxide free inverted organic solar cells based on aluminum-doped zinc oxide cathode and low-temperature aqueous solution processed zinc oxide electron extraction layer

Indium-tin-oxide (ITO) free inverted organic solar cells (IOSCs) based on aluminum-doped zinc oxide (AZO) cathode, low-temperature aqueous solution processed zinc oxide (ZnO) electron extraction layer, and poly(3-hexylthiophene-2, 5-diyl):[6, 6]-phenyl C61 butyric acid methyl ester blend were realized in this work. The resulted IOSC with ZnO annealed at 150 °C shows the superior power conversion efficiency (PCE) of 3.01%, if decreasing the ZnO annealing temperature to 100 °C, the obtained IOSC also shows a PCE of 2.76%, and no light soaking issue is observed. It is found that this ZnO film not only acts as an effective buffer layer but also slightly improves the optical transmittance of AZO substrates. Further, despite the relatively inferior air-stability, these un-encapsulated AZO/ZnO IOSCs show comparable PCEs to the referenced ITO/ZnO IOSCs, which demonstrates that the AZO cathode is a potential alternative to ITO in IOSCs. Meanwhile, this simple ZnO process is compatible with large area deposition an...

Phase separation of polyaniline blends with thermoplastic polymers

The conducting complex PANI-CSA and copolyamide (CPA) blended by casting their solutions and the ternary polymer blends PANI-CSA/CPA/LDPE were prepared via blend of PANI-CSA/CPA and LDPE in a twin-screw at 160 °C. PANI-CSA/PMMA/LDPE was also prepared. The morphology and phase separation of the ternary polymer blends were investigated by means of TEM and DSC. The components of the polymer blends were found to be incompatible and phase separation occurred.

Effects of interlayer growth condition on the transport properties of heterostructures with InGaN channel grown on sapphire by metal organic chemical vapor deposition

The effects of AlN interlayer growth condition on the properties of InAlN/InGaN heterostructures are investigated in detail. Since the properties of InGaN channel are different from the traditional GaN channel, two-step AlN interlayer is proposed, which is proven to be more suitable for the InGaN channel heterostructures than the interlayers grown at constant temperature. Test results show that two-step AlN interlayer can not only significantly improve the interface morphology between the InGaN channel and barrier layers but also make an effective protection of the high-quality InGaN channel. The electron mobility of the InAlN/InGaN heterostructure with two-step AlN interlayer achieves 890 cm2/V s with a high two-dimensional-electron-gas density of 1.78 × 1013 cm−2. The gratifying results indicate that the InGaN channel heterostructure with two-step interlayer is a promising candidate for microwave power devices.

Effects of Annealing Conditions on Mixed Lead Halide Perovskite Solar Cells and Their Thermal Stability Investigation

In this work, efficient mixed organic cation and mixed halide (MA0.7FA0.3Pb(I0.9Br0.1)3) perovskite solar cells are demonstrated by optimizing annealing conditions. AFM, XRD and PL measurements show that there is a better perovskite film quality for the annealing condition at 100 °C for 30 min. The corresponding device exhibits an optimized PCE of 16.76% with VOC of 1.02 V, JSC of 21.55 mA/cm2 and FF of 76.27%. More importantly, the mixed lead halide perovskite MA0.7FA0.3Pb(I0.9Br0.1)3 can significantly increase the thermal stability of perovskite film. After being heated at 80 °C for 24 h, the PCE of the MA0.7FA0.3Pb(I0.9Br0.1)3 device still remains at 70.00% of its initial value, which is much better than the control MAPbI3 device, where only 46.50% of its initial value could be preserved. We also successfully fabricated high-performance flexible mixed lead halide perovskite solar cells based on PEN substrates.

Efficient Bifacial Semitransparent Perovskite Solar Cells Using Ag/V2O5 as Transparent Anodes

Bifacial semitransparent inverted planar structured perovskite solar cells (PSCs) based on Cs0.05FA0.3MA0.7PbI2.51Br0.54 using an Ag thin film electrode and V2O5 optical coupling layer are investigated theoretically and experimentally. It is shown that the introduction of the cesium (Cs) ions in the perovskite could obviously improve the device performance and stability. When only the bare Ag film electrode is used, the PSCs show a bifacial performance with the power conversion efficiency (PCE) of 14.62% illuminated from the indium tin oxide (ITO) side and 5.45% from the Ag film side. By introducing a V2O5 optical coupling layer, the PCE is enhanced to 8.91% illuminated from the Ag film side, which is 63% improvement compared with the bare Ag film electrode, whereas the PCE illuminated from the ITO side remains almost unchanged. Moreover, when a back-reflector is employed, the PCE of device could be further improved to 15.39% by illumination from the ITO side and 12.44% by illumination from the Ag side. The devices also show superior semitransparent properties and exhibit negligible photocurrent hysteresis, irrespective of the side from which the light is illuminated. In short, the Ag/V2O5 double layer is a promising semitransparent electrode due to its low cost and simple preparation process, which also point to a new direction for the bifacial PSCs and tandem solar cells.

Inverted Organic Solar Cells with Low-Temperature Al-Doped-ZnO Electron Transport Layer Processed from Aqueous Solution

The aqueous-based Zn-ammine complex solutions represent one of the most promising routes to obtain the ZnO electron transport layer (ETL) at a low temperature in inverted organic solar cells (OSCs). However, to dope the ZnO film processed from the Zn-ammine complex solutions is difficult since the introduction of metal ions into the Zn-ammine complex is a nontrivial process as ammonium hydroxide tends to precipitate metal salts due to acid-base neutralization reactions. In this paper, we investigate the inverted OSCs with Al-doped-ZnO ETL made by immersion of metallic Al into the Zn-ammine precursor solution. The effects of ZnO layer with different immersion time of Al on film properties and solar cell performance have been studied. The results show that, with the Al-doped-ZnO ETL, an improvement of the device performance could be obtained compared with the device with the un-doped ZnO ETL. The improved device performance is attributed to the enhancement of charge carrier mobility leading to a decreased charge carrier recombination and improved charge collection efficiency. The fabricated thin film transistors with the same ZnO or AZO films confirm the improved electrical characteristics of the Al doped ZnO film.