Xiao-Fang Jiang

n-Type Water/Alcohol-Soluble Naphthalene Diimide-Based Conjugated Polymers for High-Performance Polymer Solar Cells

With the demonstration of small-area, single-junction polymer solar cells (PSCs) with power conversion efficiencies (PCEs) over the 10% performance milestone, the manufacturing of high-performance large-area PSC modules is becoming the most critical issue for commercial applications. However, materials and processes that are optimized for fabricating small-area devices may not be applicable for the production of high-performance large-area PSC modules. One of the challenges is to develop new conductive interfacial materials that can be easily processed with a wide range of thicknesses without significantly affecting the performance of the PSCs. Toward this goal, we report two novel naphthalene diimide-based, self-doped, n-type water/alcohol-soluble conjugated polymers (WSCPs) that can be processed with a broad thickness range of 5 to 100 nm as efficient electron transporting layers (ETLs) for high-performance PSCs. Space charge limited current and electron spin resonance spectroscopy studies confirm that the presence of amine or ammonium bromide groups on the side chains of the WSCP can n-dope PC71BM at the bulk heterojunction (BHJ)/ETL interface, which improves the electron extraction properties at the cathode. In addition, both amino functional groups can induce self-doping to the WSCPs, although by different doping mechanisms, which leads to highly conductive ETLs with reduced ohmic loss for electron transport and extraction. Ultimately, PSCs based on the self-doped WSCP ETLs exhibit significantly improved device performance, yielding PCEs as high as 9.7% and 10.11% for PTB7-Th/PC71BM and PffBT4T-2OD/PC71BM systems, respectively. More importantly, with PffBT4T-2OD/PC71BM BHJ as an active layer, a prominent PCE of over 8% was achieved even when a thick ETL of 100 nm was used. To the best of our knowledge, this is the highest efficiency demonstrated for PSCs with a thick interlayer and light-harvesting layer, which are important criteria for eventually making organic photovoltaic modules based on roll-to-roll coating processes.

11% Efficient Ternary Organic Solar Cells with High Composition Tolerance via Integrated Near-IR Sensitization and Interface Engineering.

Highly efficient electron extraction is achieved by using a photoconductive cathode interlayer in inverted ternary organic solar cells (OSCs) where a near-IR absorbing porphyrin molecule is used as the sensitizer. The OSCs show improved device performance when the ratio of the two donors varies in a large region and a maximum power conversion efficiency up to 11.03% is demonstrated.

Optimisation of processing solvent and molecular weight for the production of green-solvent-processed all-polymer solar cells with a power conversion efficiency over 9%

Increasing interest has been devoted to developing high-performance all-polymer solar cells (all-PSCs) owing to their specific advantages in light absorption and long-term stability. In this work, we systematically investigated the synergistic effects of processing solvents and molecular weight on the photovoltaic performance of all-PSCs, which consist of an n-type polymer N2200 and a p-type wide bandgap polymer PTzBI that are made up of benzodithiophene and imide-functionalized benzotriazole units. It is noted that increasing the molecular weight of N2200 can simultaneously enhance exciton generation and dissociation, reduce bimolecular recombination, and facilitate charge extraction. The films processed with the environmentally-friendly solvent 2-methyl-tetrahydrofuran (MeTHF) exhibit a more favourable film morphology than those processed with commonly used halogenated solvents. The all-PSC consisting of the high molecular weight N2200 and PTzBI processed with the environmentally friendly solvent MeTHF presents a remarkable power conversion efficiency of 9.16%, which is the highest value so far observed for all-PSCs. Of particular interest is that the PCE remains 6.37% with the active layer thickness of 230 nm. These observations imply the great promise of the developed all-PSCs for practical applications toward high-throughput roll-to-roll technology.

High-Performance Polymer Solar Cells with Electrostatic Layer-by-Layer Self-Assembled Conjugated Polyelectrolytes as the Cathode Interlayer.

An easy and efficient approach to achieve a large-area cathode interlayer with controlled film composition, uniformity, and thickness under a nanometer scale is reported by using an electrostatic layer-by-layer (eLbL) self-assembly process. The eLbL films provide a new means for preparing efficient interlayers for polymer solar cells (PSCs) and also represent a potential candidate for use in high-performance large-area PSC modules in the future.

Aqueous Solution Processed Photoconductive Cathode Interlayer for High Performance Polymer Solar Cells with Thick Interlayer and Thick Active Layer

An aqueous-solution-processed photoconductive cathode interlayer is developed, in which the photoinduced charge transfer brings multiple advantages such as increased conductivity and electron mobility, as well as reduced work function. Average power conversion efficiency over 10% is achieved even when the thickness of the cathode interlayer and active layer is up to 100 and 300 nm, respectively.

Room-temperature synthesis and warm-white LED applications of Mn4+ ion doped fluoroaluminate red phosphor Na3AlF6:Mn4+

A novel red fluoroaluminate phosphor, cryolite Na3AlF6:Mn4+, has been designed and synthesized via a facile two-step method at room temperature. Under blue light excitation, it exhibits intense sharp line red fluorescence (∼630 nm) with high color purity. The crystal structure, morphology and doping concentration of the samples were characterized in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ICP-AES. The influence of synthesis conditions, raw materials and doping concentration on crystal structure and photoluminescence (or decay behavior) has been investigated carefully. The optimal composition, Na3AlF6:1.58%Mn4+, shows a bright red light and excellent thermal stability (∼99.93% of the emission intensity at 200 °C relative to 23 °C) upon ∼467 nm blue light excitation. A warm high-power white LED with a high color rendering index (Ra = 92.7 and R9 = 94) and low color temperature (CCT = 3903 K) was fabricated based on the blue InGaN chip, commercial yellow phosphor YAG:Ce3+ and red phosphor Na3AlF6:Mn4+.

High-Performance Color-Tunable Perovskite Light Emitting Devices through Structural Modulation from Bulk to Layered Film

Adding 2-phenoxyethylamine (POEA) into a CH3 NH3 PbBr3 precursor solution can modulate the organic-inorganic hybrid perovskite structure from bulk to layered, with a photoluminescence and electroluminescence shift from green to blue. Meanwhile, POEA can passivate the CH3 NH3 PbBr3 surface and help to obtain a pure CH3 NH3 PbBr3 phase, leading to an improvement of the external quantum efficiency to nearly 3% in CH3 NH3 PbBr3 LED.

Wide bandgap dithienobenzodithiophene-based π-conjugated polymers consisting of fluorinated benzotriazole and benzothiadiazole for polymer solar cells

Two wide bandgap donor–acceptor type π-conjugated polymers based on dithienobenzodithiophene as the donor unit and difluorobenzotriazole or difluorobenzothiadiazole as the acceptor unit were designed and synthesized. The copolymer based on difluorobenzothiadiazole exhibited more pronounced aggregations in chlorobenzene solutions than that of the copolymer based on difluorobenzotriazole. Both copolymers exhibited relatively wide bandgaps with deep highest occupied molecular orbitals, leading to high open circuit voltages of over 0.95 V for the fabricated polymer solar cells. These copolymers exhibited quite analogous hole mobility of about 0.1 cm2 V−1 s−1 as measured by organic field effect transistors. Bulk heterojunction polymer solar cells based on these copolymers as the electron-donating materials and PC71BM as the electron-accepting material exhibited relatively high performance, with the best power conversion efficiency of 7.45% attained for the copolymer based on the difluorobenzothiadiazole unit. These results demonstrated that the constructed wide bandgap π-conjugated polymers can be promising candidates for the fabrication of high performance solar cells with multi-junction architectures.

Cross-Linkable and Dual Functional Hybrid Polymeric Electron Transporting Layer for High-Performance Inverted Polymer Solar Cells

A cross-linkable dual functional polymer hybrid electron transport layer (ETL) is developed by simply adding an amino-functionalized polymer dopant (PN4N) and a light crosslinker into a commercialized n-type semiconductor (N2200) matrix. It is found that the resulting hybrid ETL not only has a good solvent resistance, facilitating multilayers device fabrication but also exhibits much improved electron transporting/extraction properties due to the doping between PN4N and N2200. As a result, by using PTB7-Th:PC71 BM blend as an active layer, the inverted device based on the hybrid ETL can yield a prominent power conversion efficiency of around 10.07%. More interestingly, photovoltaic property studies of bilayer devices suggest that the absorption of the hybrid ETL contributes to photocurrent and hence the hybrid ETL simultaneously acts as both cathode interlayer material and an electron acceptor. The resulting inverted polymer solar cells function like a novel device architectures with a combination of a bulk heterojunction device and miniature bilayer devices. This work provides new insights on function of ETLs and may be open up a new direction for the design of new ETL materials and novel device architectures to further improve device performance.

Size-dependent nonlinear optical properties of black phosphorus nanosheets and their applications in ultrafast photonics

Multi-layer black phosphorus nanosheets (BPs) with different sizes are synthesized by using a basic solvent exfoliation method in association with controlled gradient centrifugation. Size-dependent nonlinear saturable absorption and Kerr nonlinearity as well as ultrafast carrier dynamics of BPs is systematically studied by using a Z-scan and pump–probe technique. Furthermore, an ultrashort pulse with a pulse duration of about 635 fs centered at a wavelength of 1562 nm is generated by using smaller sized BPs as a saturable absorber. These results directly reveal the physical processes of size-dependent nonlinear optical (NLO) properties of BPs and provide researchers with a viable approach in tailoring the NLO response of BPs through controlling the sizes, paving the way towards BP based electronics and optoelectronics applications such as ultrafast optical switches, modulators, fiber lasers, etc.