Nianqing Fu

Organic-free Anatase TiO₂ Paste for Efficient Plastic Dye-Sensitized Solar Cells and Low Temperature Processed Perovskite Solar Cells.

Recently, the synthesis of fine TiO2 paste with organic-free binder emerged as an indispensable technique for plastic photovoltaics due to the low temperature processing requirement. In this study, pure anatase TiO2 nanoparticles and organic-free TiO2-sol were successfully synthesized individually in organic-free solution. By mixing the pure anatase TiO2 with the newly developed TiO2-sol binder, mechanically robust and well-interconnected TiO2 films were prepared via UV-irradiation at low temperature for applications in plastic dye-sensitized solar cells (p-DSSCs). The structural, electrical, and photovoltaic properties of the films as well as the devices were investigated by various techniques. The dye-loading amount of the obtained film is 2.6 times that of the P25 electrodes. As revealed by electrochemical impedance spectroscopy results, the film derived from the as-prepared anatase TiO2 paste (A-TiO2) exhibits much smaller charge transport resistance and lower electron recombination rate than the P25 film, while the introduction of TiO2-sol into the paste can further remarkably decrease the resistance of the produced film (AS-TiO2). The p-DSSCs employing AS-TiO2 photoanode yield a high efficiency up to 7.51%, which is 86% higher than the P25 reference cells and also 31% higher than the A-TiO2 cell. As a proof of concept, the newly developed AS-TiO2 paste was also applied to low temperature processed perovskite solar cells (PSCs), and a promising high efficiency up to 9.95% was achieved.

Transparent Indium Tin Oxide Electrodes on Muscovite Mica for High-Temperature-Processed Flexible Optoelectronic Devices

Sn-doped In2O3 (ITO) electrodes were deposited on transparent and flexible muscovite mica. The use of mica substrate makes a high-temperature annealing process (up to 500 °C) possible. ITO/mica retains its low electric resistivity even after continuous bending of 1000 times on account of the unique layered structure of mica. When used as a transparent flexible heater, ITO/mica shows an extremely fast ramping (<15 s) up to a high temperature of over 438 °C. When used as a transparent electrode, ITO/mica permits a high-temperature annealing (450 °C) approach to fabricate flexible perovskite solar cells (PSCs) with high efficiency.

Enhancing the performance of dye-sensitized solar cells: doping SnO2 photoanodes with Al to simultaneously improve conduction band and electron lifetime

SnO2 is an important alternative to TiO2 for use as a semiconductor in dye-sensitized solar cell (DSSC) photoanodes. In this work, we prepared SnO2 and Al-doped SnO2 nanocrystals via a simple hydrothermal method, and found for the first time that the tuning of the conduction band and suppression of charge recombination are simultaneously improved in the Al-doped samples. The electron lifetime is significantly improved and the conduction band edge is shifted negatively by doping the SnO2 photoanode with Al. Compared to the undoped SnO2 DSSCs (AM 1.5, 100 mW cm−2), the power conversion efficiency (η) of the optimized Al-doped SnO2 DSSCs is enhanced by 75%. After being treated with TiCl4, the highest η of DSSCs based on Al-doped SnO2 nanocrystals is approximately 6.91%, which is a high overall photoconversion efficiency for SnO2-based DSSCs.

Metal and F dual-doping to synchronously improve electron transport rate and lifetime for TiO2 photoanode to enhance dye-sensitized solar cells performances

A general strategy to synchronously improve electron transport rate and lifetime for TiO2 photoanode by metal and F− dual doping is proposed and demonstrated for dye-sensitized solar cells (DSSCs) for the first time. Tin and fluorine dual-doped TiO2 nanoparticles are prepared and X-ray photoelectron spectroscopy (XPS) analysis indicates that the Sn atoms and the F atoms locate mainly in the TiO2 lattice and on the TiO2 particles surface, respectively. The DSSC based on Sn/F–TiO2 sample shows a high photoconversion efficiency of 8.89% under an AM 1.5 solar condition (100 mW cm−2), which is higher than those for the undoped TiO2 nanoparticles (7.12%) and the solely Sn (8.14%) or F doped (8.31%) samples. This improvement is attributed to the combined effects of a faster electron transport rate and a longer electron lifetime in the dual-doped TiO2 film. Following this strategy, we also prepare Ta/F, Nb/F, and Sb/F dual-doped TiO2 nanoparticles and find that the performance of DSSCs based on all the dual-doped samples is further improved compared with the single doping cases. Finally, through density functional theory (DFT) calculations, the mechanism behind the improvement by tin and fluorine dual-doping is discussed in detail.

Facile preparation of hierarchical TiO2 nanowire–nanoparticle/nanotube architecture for highly efficient dye-sensitized solar cells

In the present work, we developed a facile post-treatment approach, namely one-step hot-water soaking, to the fabrication of double-layer and hierarchical TiO2 nanotube arrays (H-TNTAs) comprising a nanoparticle/nanotube hybrid layer and a TiO2 nanowire cap layer for highly efficient dye-sensitized solar cells (DSSCs). The nanoparticle/nanotube hybrid structure of the H-TNTA provides enormous specific surface area for sufficient dye attachment and the TiO2 nanowire cap layer serves as a light-scattering layer with increased dye-absorption for superior light harvesting efficiency. This engineered integration makes it possible to control the dye-anchoring, charge transport, charge collection, and light scattering within a photoanode simultaneously. The DSSC based on the well tailored architecture yields an exciting power conversion efficiency of 8.21% under 100 mW cm−2, corresponding to 51% improvement as compared with the cell built on the pristine TNTA (P-TNTA, 5.43%). The efficiency can be further improved to 8.82% when the H-TNTA photoanodes are subjected to an additional TiCl4 treatment.

Ni@NiO core/shell dendrites for ultra-long cycle life electrochemical energy storage

A dendritic Ni@NiO core/shell electrode (DNE) is successfully fabricated by electrodeposition in a Ni-free electrolyte, with a Ni anode providing Ni ions through dissolution and diffusion. The unique structure is ideal for electrochemical energy storage since the dendrites provide a large surface area for easy electrolyte infiltration; the metal core improves the electrode conductivity with a shortened ion diffusion path, and the metal oxide shell is active for faradaic charge storage. As a result, the synthesized DNE demonstrates a high specific capacitance of 1930 F g−1 and a high areal capacitance of 1.35 F cm−2, with super-long cycle stability. The gravimetric capacitance of the DNE hardly shows any decay after 70 000 cycles at a scan rate of 100 mV s−1. It was also demonstrated that our electrodeposition method in a source-free electrolyte is universal to deposit dendritic Ni-compounds on many other types of substrates, versatile for different applications.

Effects of Ga doping and hollow structure on the band-structures and photovoltaic properties of SnO2 photoanode dye-sensitized solar cells

The photon-to-electricity conversion properties of the prepared photoanode based on SnO2 nanocrystals, which are assembled as the rough hollow microspheres (RHMs), are improved by aliovalent Ga3+ doping. The conduction band (CB) of the doped SnO2 shifts negatively with increasing the Ga content from 1 to 5 mol% gradually. Moreover, the prepared Ga-doped SnO2 photoanode shows an advantage in repressing the charge recombination. As a result, both the negative shift of the CB and repressed charge recombination enhance the open-circuit photovoltage (Voc) and the short-circuit photocurrent (Jsc) of the DSSCs, and the power conversion efficiency (η) is increased by 80% at 3 mol% Ga-doping SnO2 to compare with the undoped SnO2 for DSSCs (AM 1.5, 100 mW cm−2). After treating the samples with TiCl4, an overall photoconversion efficiency (approximately 7.11%) for SnO2 based DSSCs is achieved.

Hybrid n-type Sn1−xTaxO2 nanowalls bonded with graphene-like layers as high performance electrocatalysts for flexible energy conversion devices

We report here hybrid n-type Ta-doped SnO2 (Sn1−xTaxO2) nanowalls (as an electron-rich donor) bonded with graphene-like layers (Sn1−xTaxO2/C) as high performance electrocatalysts for flexible energy conversion devices. SnO2 possesses high electron mobility (125–250 cm2 V−1 S−1), and Ta doping is adopted to increase the electron concentration to further improve the conductivity of the SnO2 film to allow its use as a catalyst support. Our first-principles calculations reveal that the increased electrical conductance is mainly attributed to the increased intrinsic doping effect caused by the substitution of Sn by Ta. The Ta-doped SnO2 not only acts a well conductive support for the close coated graphene-like carbon layers but also pushes electrons to the carbon electrocatalyst to enhance its catalytic performance. Advanced features of these nanowall films include not only a high specific surface area, and good adhesion to substrates, but also flexibility. One application as a counter electrode in fully flexible dye-sensitized solar cells (DSSCs) shows that the optimal power conversion efficiency (PCE) of fully flexible DSSCs is 8.38% under AM1.5G illumination (100 mW cm−2), which is one of the highest PCEs for fully flexible DSSCs.

One-pot fabrication of Nitrogen-doped graphene supported binary palladium-sliver nanocapsules enable efficient ethylene glycol electrocatalysis

Fuel cells hold great potential of replacing traditional fossil fuel to alleviate the energy crisis and increasing environmental concerns. Although great progresses have been achieved over decades, the sluggish reaction kinetics and poor durability of electrocatalysts in fuel cells have been the decisive bottleneck that limited their practical applications. Herein, we focus on the design and development of cost-efficient anode electrocatalysts for fuel cells and report the successful creation of an advanced class of N-doped graphene (NG) supported binary PdAg nanocapsules (PdAg NCPs). The well-defined nanocatalysts with highly open structure exhibit greatly improved electrocatalytic performances for ethylene glycol oxidation reaction (EGOR). In particular, the optimized PdAg NCPs/NG show the mass and specific activities of 6118.3 mA mg-1 and 13.8 mA cm-2, which are 5.8 and 6.9 times larger than those of the commercial Pd/C catalysts, respectively. More importantly, such PdAg NCPs/NG can also maintain at least 500 potential cycles with limited catalytic activity attenuation, showing an advanced class of electrocatalysts for fuel cells.

Boosting the oxygen evolution reaction in non-precious catalysts by structural and electronic engineering

The oxygen evolution reaction (OER) plays a key role in many energy storage applications. It remains a big challenge to fabricate non-precious OER electrocatalysts with both excellent activity and high stability. Herein, we demonstrate that excellent OER performance can be achieved by applying structural and electronic engineering simultaneously. As a proof of concept, 1D vertically aligned Ni3S2 nanorods (without any entangled or inter-crossed nanostructure on the top) are firstly synthesized to provide both conducting highways and rich active sites with significantly facilitated gas release during the OER. A highly active Ni–Fe layered double hydroxide (LDH) nanofilm is then prepared on the Ni3S2 nanorod to form a core@shell structure. The strong interfacial coupling between the in situ grown Ni–Fe LDH and Ni3S2 creates abundant oxygen vacancies to effectively lower the adsorption energy of OH−. Consequently, Ni3S2@Ni–Fe LDH exhibits superior OER activity and outstanding stability. The overpotential of Ni3S2@Ni–Fe LDH prepared on nickel foam is only 190 mV at 10 mA cm−2 and the Tafel slope is as low as 38 mV dec−1. The OER performance remains constant after 40 hours of water electrolysis. Our material is among the best non-precious OER catalysts reported so far. The methodology of enhancing the catalytic performance reported here can be extended to other materials for the design and fabrication of low cost OER catalysts with excellent activity.